soil microenvironment for
TRANSCRIPT
Soil Microenvironment for Bioremediation and Polymer Production
Scrivener Publishing100 Cummings Center, Suite 541J
Beverly, MA
Publishers at ScrivenerMartin Scrivener ([email protected])
Phillip Carmical ([email protected])
Soil Microenvironment for
Bioremediation and Polymer Production
Edited byNazia Jamil, Prasun Kumar
and Rida Batool
This edition first published 2020 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2020 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
Wiley Global Headquarters
111 River Street, Hoboken, NJ 07030, USA
For details of our global editorial offices, customer services, and more information about Wiley prod-ucts visit us at www.wiley.com.
Limit of Liability/Disclaimer of Warranty
While the publisher and authors have used their best efforts in preparing this work, they make no rep resentations or warran-ties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchant- ability or fitness for a particular purpose. No warranty may be created or extended by sales representa tives, written sales materials, or promotional statements for this work. The fact that an orga-nization, website, or product is referred to in this work as a citation and/or potential source of further informa tion does not mean that the publisher and authors endorse the information or services the organiza tion, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering pro-fessional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read.
Library of Congress Cataloging-in-Publication Data
Name: Jamil, Nazia, editor.Title: Soil microenvironment for bioremediation and polymer production / edited by Nazia Jamil, Prasun Kumar and
Rida Batool.Description: First edition. | Hoboken, NJ : Wiley-Scrivener, 2020. | Includes bibliographical references and index. Identifiers: LCCN 2019040532 (print) | LCCN 2019040533 (ebook) | ISBN 9781119592051 (hardback) | ISBN 9781119592150
(adobe pdf) | ISBN 9781119592174 (epub)Subjects: LCSH: Soil microbiology. | Soil remediation. | Bioremediation. Classification: LCC QR111 .S6735 2020 (print) | LCC QR111 (ebook) | DDC 579/.1757--dc23 LC record available at https://lccn.loc.gov/2019040532LC ebook record available at https://lccn.loc.gov/2019040533
Cover image: Pixabay.ComCover design by Russell Richardson
Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines
Printed in the USA
10 9 8 7 6 5 4 3 2 1
v
Contents
Preface xvii
Part 1: Soil Microenvironment and Biotransformation Mechanisms 1
1 Applications of Microorganisms in Agriculture for Nutrients Availability 3
Fehmida Fasim and Bushra Uziar1.1 Introduction 3
1.1.1 Land and Soil Deterioration 41.1.2 Micro-Nutrients Lacks 4
1.2 Biofertilizers 41.3 Rhizosphere 51.4 Plant Growth Promoting Bacteria 5
1.4.1 Nitrogen Fixation 61.4.2 Phosphate Solubilization 8
1.5 Microbial Mechanisms of Phosphate Solubilization 91.5.1 Organic Phosphate 9
1.5.1.1 Organic Acid Production 91.5.1.2 Inorganic Acid Production 101.5.1.3 Enzymes Production 10
1.5.2 Organic Phosphate Solubilization 101.6 Bacterial and Fungi Coinoculation 111.7 Conclusion 11 References 12
2 Native Soil Bacteria: Potential Agent for Bioremediation 17
Ranjan Kumar Mohapatra, Haragobinda Srichandan, Snehasish Mishra and Pankaj Kumar Parhi2.1 Introduction 172.2 Current Soil Pollution Scenario 19
2.2.1 Soil Pollution by Heavy Metals and Xenobiotic Compounds 192.2.2 Soil Pollution by Extensive Agricultural and
Animal Husbandry Practices 202.2.3 Pollution Due to Emerging Pollutants (Wastes from Pharmaceutical
and Personal-Care Products) 212.2.4 Soil Pollution by Pathogenic Microorganisms 22
vi Contents
2.2.5 Soil Pollution Due to Oil and Petroleum Hydrocarbons 232.2.6 Soil Pollution by the Nuclear and Radioactive Wastes 252.2.7 Soil Pollution by Military Activities and Warfare 26
2.3 Effects of Soil Pollution 262.3.1 Effects of Soil Pollution on Plants 262.3.2 Effects of Soil Pollution on Human Health 26
2.4 Diversity of Soil Bacteria from Contaminated Sites 272.5 Bioremediation of Toxic Pollutants 272.6 Bioremediation Mechanisms 272.7 Factors Affecting Bioremediation/Biosorption Process 292.8 Microbial Bioremediation Approaches 30
2.8.1 In Situ Bioremediation 302.8.2 Ex Situ Bioremediation 30
2.9 Conclusion and Future Prospective 30 Acknowledgements 30 References 31
3 Bacterial Mediated Remediation: A Strategy To Combat Pesticide Residues In Agricultural Soil 35
Atia Iqbal3.1 Introduction 353.2 Effects of Pesticides 363.3 Pesticide Degradation 373.4 Bacterial Mediated Biodegradation of Various Pesticides 38
3.4.1 Organophosphate Pesticides Degrading Bacteria 383.4.2 Methyl Parathion Mineralizing Bacteria (MP) 393.4.3 Mesotrione Degrading Bacteria 393.4.4 Aromatic Hydrocarbons Biodegradation 393.4.5 Bispyribac Sodium (BS) Degrading Bacteria 403.4.6 Carbamates (CRBs) Degradation 403.4.7 Propanil Degradation 403.4.8 Atrazine Degradation 403.4.9 Phenanthrene Degradation 403.4.10 Imidacloprid Degradation 413.4.11 Endusulfan Degradation 413.4.12 DDT 42
3.5 Conclusion 42 References 49
4 Study of Plant Microbial Interaction in Formation of Cheese Production: A Vegan’s Delight 55
Sundaresan Bhavaniramya, Ramar Vanajothi, Selvaraju Vishnupriya and Dharmar Baskaran4.1 Introduction 554.2 Cheese Concern – Vegan’s Delight 574.3 Microorganism Interaction Pattern 57
Contents vii
4.4 Types of Microorganism Involved in Cheese Production 574.5 Lactic Acid Role in Fermentation 594.6 Microorganism Involved in Lactic Acid Fermentation 594.7 Streptococcus 604.8 Propionibacterium 604.9 Leuconostoc 604.10 Microorganisms in Flavor Development 614.11 Flavor Production 634.12 Enzymes Interaction during Ripening of Cheese 634.13 Pathways Involved in Cheese Ripening 644.14 Microbes of Interest in Flavor Formation 664.15 Structure of Flavored Compound in Cheese 674.16 Plant-Based Cheese Analogues 674.17 Plant-Based Proteins 684.18 Aspartic Protease 694.19 Cysteine Protease 694.20 Plant-Based Milk Alternatives 694.21 Types of Vegan Cheese 704.22 Future Scope and Conclusion 71 Acknowledgment 71 References 71
5 Microbial Remediation of Pesticide Polluted Soils 75
César Quintela and Cristiano Varrone5.1 Introduction 755.2 Types of Pesticides 775.3 Fate of Pesticides in the Environment 81
5.3.1 Factors Affecting Pesticide Fate 815.3.2 Pesticides Degradation 84
5.3.2.1 Abiotic Degradation 845.3.2.2 Biodegradation 84
5.3.3 Pesticide Remediation 855.4 Screening for Pesticide Degrading Microorganisms 85
5.4.1 Case Study 865.5 Designing Pesticide Degrading Consortia 87
5.5.1 Case Study 885.6 Challenges to be Addressed and Future Perspectives 88 References 90
6 Eco-Friendly and Economical Method for Detoxification of Pesticides by Microbes 95
Anjani Kumar Upadhyay, Abhik Mojumdar, Vishakha Raina and Lopamudra Ray6.1 Introduction 956.2 Classification of Pesticides 966.3 Fate of Pesticide in Soil 96
viii Contents
6.3.1 Transport of Pesticides in the Environment 966.3.2 Interaction of Pesticides with Soil 98
6.4 Microbial and Phytoremediation of Pesticides 996.4.1 Biodegradation and Bioremediation 996.4.2 Microbial Remediation of Pesticides 1026.4.3 Phytoremediation of Pesticides 1036.4.4 Strategies to Enhance the Efficiency of Bioremediation 103
6.4.4.1 Biostimulation 1036.4.4.2 Bioaugmentation 1046.4.4.3 Genetically Engineered Microorganisms (GEMs) 104
6.4.5 Metabolic Aspects of Pesticides Bioremediation 1056.5 Effects on Human and Environment 1066.6 Advancement in Pesticide Bioremediation 1076.7 Limitations of Bioremediation 1076.8 Future Perspectives 108 Acknowledgement 108 References 108
Part 2: Synergistic Effects Between Substrates and Microbes 115
7 Bioleaching: A Bioremediation Process to Treat Hazardous Wastes 117
Haragobinda Srichandan, Ranjan K. Mohapatra, Pankaj K. Parhi and Snehasish Mishra7.1 Introduction 1177.2 Microbes in Bioleaching 118
7.2.1 Bacteria 1187.2.2 Fungi 119
7.3 Acidophilic Bioleaching 1197.3.1 Contact (Direct) Mechanism 1197.3.2 Non-Contact (Indirect) Mechanism 120
7.4 Metal Removal Pathways 1207.4.1 Thiosulphate Pathway 1207.4.2 Polysulphide Pathway 121
7.5 Fungal Bioleaching 1227.6 Various Hazardous Wastes 122
7.6.1 Electronic Wastes (E-Wastes) 1237.6.2 Spent Petroleum Catalyst 1237.6.3 Sludge 1237.6.4 Slag 123
7.7 Applications of Bioleaching Approach to Various Hazardous Wastes 1237.7.1 Bioleaching of Electronic Wastes 1247.7.2 Bioleaching of Spent Catalyst 1247.7.3 Bioleaching of Sludge (Containing Heavy or Toxic metals) 1257.7.4 Bioleaching of Slag 125
7.8 Conclusion 126 Acknowledgements 126 References 126
Contents ix
8 Microbial Bioremediation of Azo Dyes in Textile Industry Effluent: A Review on Bioreactor-Based Studies 131
Shweta Agrawal, Devayani Tipre and Shailesh Dave8.1 Introduction 1318.2 Microorganism Involved in Dye Bioremediation 132
8.2.1 Bacterial Remediation of Dyes 1328.2.2 Mycoremediation 1358.2.3 Phycoremediation 1358.2.4 Consortial (Co-Culture) Dye Bioremediation 135
8.3 Mechanism of Dye Biodegradation 1398.3.1 Anaerobic Azo Dye Reduction 1398.3.2 Aerobic Oxidation of Aromatic Amines 1408.3.3 Combined Anaerobic-Aerobic Treatment of Azo Dyes 141
8.4 Reactor Design for Dye Bioremediation 1418.4.1 Anaerobic Reactors 142
8.4.1.1 Upflow Anaerobic Sludge Blanket (UASB) 1488.4.1.2 Upflow Anaerobic Fixed Bed (UAFB) Reactor 1498.4.1.3 Sequencing Batch Reactor (SBR) 1498.4.1.4 Anaerobic Baffled Reactor (ABR) 1518.4.1.5 Membrane Bioreactor (MBR) 1518.4.1.6 Packed Bed Reactor (PBR) 1528.4.1.7 Fluidized Bed Reactor (FBR) 1538.4.1.8 Fixed Film Reactor (FFR) 154
8.4.2 Aerobic Reactors 1548.4.2.1 Rotating Biological Contactor (RBC) 1548.4.2.2 Airlift Reactor (ALR) 1568.4.2.3 Membrane-Aerated Biofilm Reactor 156
8.4.3 Combined (Integrated/Sequential) Bioreactor 1578.4.3.1 Sequential Anaerobic-Aerobic Process 1578.4.3.2 Integrated Anaerobic/Aerobic 158
8.4.4 Combinatorial Approaches 1628.5 Limitations and Future Prospects 1638.6 Conclusions 163 References 164
9 Antibiofilm Property of Biosurfactant Produced by Nesterenkonia sp. MCCB 225 Against Shrimp Pathogen, Vibrio harveyi 173
Gopalakrishnan Menon, Issac Sarojini Bright Singh, Prasannan Geetha Preena and Sumitra Datta9.1 Introduction 1739.2 Materials and Methods 174
9.2.1 Isolation, Screening and Identification of Bacteria 1749.2.1.1 Haemolytic Activity 1749.2.1.2 Lipolytic Activity 1759.2.1.3 Biosurfactant Production 175
9.2.2 Biofilm Disruption Studies 175
x Contents
9.3 Results and Discussion 1759.3.1 Bacterial Identification 1759.3.2 Biofilm Disruption Studies 175
9.4 Conclusion 178 Acknowledgements 178 References 178
10 Role of Cr (VI) Resistant Bacillus megaterium in Phytoremediation 181
Rabia Faryad Khan and Rida Batool10.1 Introduction 18110.2 Materials and Methods 183
10.2.1 Isolation and Characterization of Chromate Resistant Bacteria 18310.2.2 Determination of MIC (Minimum Inhibitory Concentration)
of Chromate 18310.2.3 Ribo-Typing of Bacterial Isolate rCrI 18310.2.4 Estimation of Chromate Reduction Potential 18310.2.5 Antibiotic and Heavy Metal Resistance Profiling 18310.2.6 Growth Curve Studies 184
10.2.6.1 Plant Microbe Interaction Studies 18410.2.6.2 Inoculum Preparation 18410.2.6.3 Experimental Design Under Laboratory Conditions 18410.2.6.4 Experimental Design Under Field Conditions 18410.2.6.5 Harvesting 18410.2.6.6 Biochemical Analysis 18510.2.6.7 Estimation of Peroxidase Activity 18510.2.6.8 Extraction and Estimation of Auxin 18510.2.6.9 Soluble Protein Extraction for Protein Estimation 185
10.2.7 Chromium Uptake Estimation 18510.2.8 Statistical Analysis 185
10.3 Results 18510.3.1 Isolation and Characterization of Cr(VI) Resistant Bacterial Isolates 18510.3.2 Antibiotic and Heavy Metal Resistance Profiling 18610.3.3 Estimation of Cr(VI) Reduction Potential 18610.3.4 Ribo-Typing of Bacterial Isolate 18610.3.5 Growth Curve Studies 18610.3.6 Plant Microbe Interaction Studies Under Laboratory Conditions 187
10.3.6.1 Seed Germination 18710.3.6.2 Shoot Length 18710.3.6.3 Root Length 18810.3.6.4 Number of Roots 188
10.3.7 Biochemical Parameters 18810.3.7.1 Peroxidase Content 18810.3.7.2 Auxin Content 18910.3.7.3 Soluble Protein Content 18910.3.7.4 Chromium Content 190
10.3.8 Plant Microbe Interaction Studies Under Field Conditions 19010.3.8.1 Seed Germination 190
Contents xi
10.3.8.2 Shoot Length 19010.3.8.3 Root Length 19010.3.8.4 Number of Roots 190
10.3.9 Biochemical Parameters 19010.3.9.1 Peroxidase Content 19010.3.9.2 Auxin Content 19110.3.9.3 Soluble Protein Content 19110.3.9.4 Chromium Content 191
10.4 Discussion 19110.5 Conclusion 193 Acknowledgment 193 References 193
11 Conjugate Magnetic Nanoparticles and Microbial Remediation, a Genuine Technology to Remediate Radioactive Waste 197
Bushra Uzair, Anum Shaukat, Fehmida Fasim, Sadaf Maqbool11.1 Introduction 19711.2 Use of Magnetic Nanoparticles Conjugates 199
11.2.1 Potential Benefits 19911.2.2 Synthesis and Application 20011.2.3 Factors Affecting Sorption 20011.2.4 Limitations 203
11.3 Microbial Communities 20311.3.1 Fungi as Radio-Nuclides Remade 20311.3.2 Immobilization of Radionuclide Through Enzymatic Reduction 20411.3.3 Immobilization Through Non-Enzymatic Reduction 20411.3.4 Bio-Sorption of Radio-Nuclides 20511.3.5 Biostimulation 20611.3.6 Genetically Modified Microbes 20611.3.7 Constraints 207
11.4 Conclusion 207 References 208
Part 3: Polyhydroxyalakanoates: Resources, Demands and Sustainability 213
12 Microbial Degradation of Plastics: New Plastic Degraders, Mixed Cultures and Engineering Strategies 215
Samantha Jenkins, Alba Martínez i Quer, César Fonseca and Cristiano Varrone12.1 Introduction 21512.2 Plastics 216
12.2.1 Polyethylene Terephthalate (PET) 21712.2.2 Low-Density Polyethylene (LDPE) 217
12.3 Plastic Disposal, Reuse and Recycling 21812.4 Plastic Biodegradation 219
12.4.1 Plastic-Degrading Microorganisms and Enzymes 221
xii Contents
12.4.2 Biofilms and Plastic Biodegradation 22412.4.3 Boosting Plastic Biodegradation by Physical and
Chemical Processes 22512.4.4 Pathway and Protein Engineering for Enhanced
Plastic Biodegradation 22612.4.5 Designing Plastic Degrading Consortia 229
12.5 Analytical Techniques to Study Plastic Degradation 23012.6 Future Perspectives 232 References 233
13 Fatty acids as Novel Building-Blocks for Biomaterial Synthesis 239
Prasun Kumar13.1 Introduction 23913.2 Polyurethane (PUs) 24113.3 Polyhydroxyalkanoates (PHAs) 24313.4 Other Functional Attributes 246
13.4.1 Biosurfactants 24613.4.2 Antibacterials and Biocontrol Agents 246
13.5 Future Perspectives 249 References 249
14 Polyhydroxyalkanoates: Resources, Demands and Sustainability 253
Binita Bhattacharyya, Himadri Tanaya Behera, Abhik Mojumdar, Vishakha Raina and Lopamudra Ray14.1 Introduction 25314.2 Polyhydroxyalkanoates 255
14.2.1 Properties of PHAs 25814.2.2 Production of PHA 26114.2.3 PHA Biosynthesis in Natural Isolates 26114.2.4 Production of PHA by Digestion of Biological Wastes 26214.2.5 PHA Production by Recombinant Bacteria 26214..2.6 Production of PHA by Genetically Engineered Plants 26414.2.7 PHA Production by Methylotrophs 26414.2.8 PHA Production Using Waste Vegetable Oil by
Pseudomonas sp. Strain DR2 26414.2.9 Mass Production of PHA 265
14.3 Applications of PHA 26614.4 Future Prospects 267 References 267
15 Polyhydroxyalkanoates Synthesis by Bacillus aryabhattai C48 Isolated from Cassava Dumpsites in South-Western, Nigeria 271
Fadipe Temitope O., Nazia Jamil and Lawal Adekunle K.15.1 Introduction 27115.2 Materials and Methods 272
15.2.1 Morphological, Biochemical and Molecular Characterisation 272
Contents xiii
15.2.2 Detection of PHA Production 27315.2.3 Evaluation of PHA Production 27315.2.4 Extraction of PHA 27315.2.5 Fourier Transform Infrared Spectroscopy of Extracted PHA 27415.2.6 Amplification of PhaC and PhaR Genes of Bacillus aryabhattai C48 274
15.3 Results and Discussion 27415.4 Conclusion 280 Acknowledgements 280 References 280
Part 4: Cellulose-Based Biomaterials: Benefits and Challenges 283
16 Cellulose Nanocrystals-Based Composites 285
Teboho Clement Mokhena, Maya Jacob John, Mokgaotsa Jonas Mochane, Asanda Mtibe, Teboho Simon Motsoeneng, Thabang Hendrica Mokhothu and Cyrus Alushavhiwi Tshifularo16.1 Introduction 28516.2 Classification of Polymers 28616.3 Preparation of Cellulose Nanocrystals Composites 286
16.3.1 Solution Casting 28716.3.2 Three Dimensional Printing (3D-Printing) 29216.3.3 Electrospinning 29416.3.4 Other Processing Techniques 294
16.4 Cellulose Nanocrystals Reinforced Biopolymers 29416.4.1 Starch 29416.4.2 Alginate 29516.4.3 Chitosan 29616.4.4 Cellulose 29716.4.5 Other Biopolymers 298
16.5 Hybrids 29816.6 Conclusion and Future Trends 300 Acknowledgements 300 References 300
17 Progress on Production of Cellulose from Bacteria 307
Tladi Gideon Mofokeng, Mokgaotsa Jonas Mochane, Vincent Ojijo, Suprakas Sinha Ray and Teboho Clement Mokhena17.1 Introduction 30717.2 Production of Microbial Cellulose (MC) 30817.3 Applications of Microbial Cellulose (MC) 312
17.3.1 Skin Therapy and Wound Healing System 31317.3.2 Scaffolds for Artificial Cornea 31417.3.3 Cardiovascular Implants 315
Future Perspective 315 References 316
xiv Contents
18 Recent Developments of Cellulose-Based Biomaterials 319
Asanda Mtibe, Teboho Clement Mokhena, Thabang Hendrica Mokhothu and Mokgaotsa Jonas Mochane18.1 Introduction 31918.2 Extraction of Cellulose Fibers 32018.3 Nanocellulose 32418.4 Surface Modification 327
18.4.1 Alkali Treatment (Mercerization) 32718.4.2 Silane Treatment 32818.4.3 Acetylation 328
18.5 Cellulose-Based Biomaterials 32918.5.1 Cellulose-Based Biomaterials for Tissue Engineering 32918.5.2 Cellulose-Based Biomaterials for Drug Delivery 33118.5.3 Cellulose-Based Biomaterials for Wound Dressing 332
18.6 Summary and Future Prospect of Cellulose-Based Biomaterials 333 Reference 334
19 Insights of Bacterial Cellulose: Bio and Nano-Polymer Composites Towards Industrial Application 339
Vishnupriya Selvaraju, Bhavaniramya Sundaresan, Baskaran Dharmar19.1 Introduction 339
19.1.1 Nanocellulose 34019.1.1.1 Cellulose Nanocrystals (CNC) 34019.1.1.2 Cellulose Nanofibrils (CNF) 341
19.2 Bacterial Cellulose 34319.2.1 Bacterial Strains Producing Cellulose 34319.2.2 Different Methods of Bacterial Cellulose Production 344
19.3 Nanocomposites 34619.3.1 Bio-Nanocomposite-Based on CNF 34619.3.2 Bio-Nanocomposite-Based on CNC 34619.3.3 Bacterial Cellulose Nanocomposites 346
19.4 Methods of Synthesis of Bacterial Cellulose Composites 34719.5 Combination of Bacterial Cellulose with Other Materials 349
19.5.1 Polymer 34919.5.2 Metals and Solid Materials 350
19.6 Industrial Applications of Bacterial Cellulose Composites 35019.6.1 Biomedical Applications 35019.6.2 Food Application 35119.6.3 Electrical Industry 351
19.7 Future Scope and Conclusion 352 Acknowledgement 352 References 352
Contents xv
20 Biodegradable Polymers Reinforced with Lignin and Lignocellulosic Materials 357
M.A. Sibeko, V.C. Agbakoba, T.C. Mokhena, P.S. Hlangothi20.1 Introduction 35720.2 Biodegradable Polymers 358
20.2.1 Natural Polymers 35920.2.1.1 Polysaccharides 35920.2.1.2 Proteins 359
20.2.2 Biodegradable Polyesters 36020.2.2.1 Polyesters Originated from Agro-Resources 36020.2.2.2 Polyesters Based on Petroleum Products 361
20.2.3 Biodegradation 36220.2.3.1 Mechanism of Biodegradation 36220.2.3.2 Factors Affecting Biodegradation 362
20.3 Biodegradable Fillers 36220.3.1 Plant Fibers as Biodegradable Fillers 36320.3.2 Cellulose as Biodegradable Fillers 36420.3.3 Lignin as Biodegradable Fillers 364
20.4 Properties of Different Biopolymers Reinforced with Lignin 36520.4.1 Surface Morphology 36520.4.2 Mechanical Properties 36620.4.3 Thermal Properties 368
20.5 Applications of Bio-Nanocomposites 369 Concluding Remarks 369 Acknowledgements 370 References 370
21 Structure and Properties of Lignin-Based Biopolymers in Polymer Production 375
Teboho Simon Motsoeneng, Mokgaotsa Jonas Mochane,
Teboho Clement Mokhena and Maya Jacob John21.1 Introduction 37521.2 An Insight on the Biopolymers 376
21.2.1 Natural Lignin Biopolymer 37721.2.2 Drawbacks of Lignin Biopolymer 378
21.3 Extraction and Post-Treatment of Lignin Biomaterial 37821.3.1 Extraction Methods and their Effect on the
Recovery and Functionality 37921.3.1.1 Milled Wood Lignin (MWL) 37921.3.1.2 Mild Acidolysis Lignin (MAL) 37921.3.1.3 Cellulolytic Enzymes Lignin (CEL) 37921.3.1.4 Enzymatic Mild Acidolysis Lignin (EMAL) 38021.3.1.5 Kraft Lignin (KL) 38021.3.1.6 Lignosulphonate (LS) 38021.3.1.7 Soda Lignin (SL) 38021.3.1.8 Organosolv Lignin (OSL) 381
21.3.2 Modification of Lignin Functional Groups 381
xvi Contents
21.3.3 Preparation of Lignin-Based Biopolymers Blends (LBBs) 38321.3.3.1 Synthesis of Binary LBBs 38521.3.3.2 Synthesis of Ternary LBBs 385
21.4 Characterization Methods and Validation of Lignin-Biopolymers 38621.4.1 Chemical Interaction Between Lignin and Synthetic Polymers 38621.4.2 Morphology-Property Relationship of the LBB 387
21.5 Indispensability of LBB on the Chemical Release Control in the Environment 388
21.6 Conclusion and Future Remarks 388 References 389
Index 393
xvii
Preface
Microenvironmental conditions in soil provide a natural niche for ultra structures, microbes and microenvironments. These microenvironments surrounding microbial substrates are very crucial for synergistic exchanges. The natural biodiversity of these microenvironments is being disturbed by industrialization and the proliferation of urban centers; and synthetic contaminants found in these micro-places are causing stress and instability in the bio-chemical systems of microbes. The development of new metabolic pathways from intrinsic metabolic cycles facilitates microbial degradation of diverse resistant synthetic compounds present in soil. These are a vital, competent and cost-effective substitute to conventional treatments. At the moment, highly developed techniques for bioremediation of these syn-thetic compounds are on the rise. These techniques facilitate the development of a safe envi-ronment using renewable biomaterial for removal of toxic heavy metals and xenobiotics.
The current book presents research data and reviews under the title of Soil Microenvironment for Bioremediation and Polymer Production. Included in the chapters are classical bioremediation approaches and advances in the use of nanoparticles for removal of radioactive waste. The chapters included in Parts 3 and 4 discuss the production of applied emerging biopolymers using diverse microorganisms. All chapters are supplemented with comprehensive illustrative diagrams and comparative tables. This book will be beneficial for both beginners and experts in the field of applied microbial bioremediation and renewable biomaterials. It is our hope that by reading this book researchers and conservationists will be inspired to apply microbial bioremediation and renewable biomaterial. Finally, we wish to thank all the authors with expertise in this field of research for their valuable contribu-tions in making this a successful venture.
Nazia JamilPrasun Kumar
Rida BatoolOctober 2019
Part 1
SOIL MICROENVIRONMENT AND
BIOTRANSFORMATION MECHANISMS
3
Nazia Jamil, Prasun Kumar and Rida Batool (eds.) Soil Microenvironment for Bioremediation and Polymer Production, (3–16) © 2020 Scrivener Publishing LLC
1
Applications of Microorganisms in Agriculture for Nutrients Availability
Fehmida Fasim1* and Bushra Uziar2
1Discipline of Biomedical Science, Sydney Medical School, University of Sydney, Australia2International Islamic University, Department of Bioinformatics and Biotechnology,
Islamabad Capital Territory, Islamabad
AbstractConstantly increasing global food demand, over use of Phosphorus (P) containing fertilisers to improve agricultural productivity not only causes pollution of ground and surface water but also depletes soil fertility and leads to accumulation of toxic elements in the soil. Production of healthy agriculture crops is essentially dependant on the available nutrients in soil. In healthy crop produc-tion, key nutrients such as phosphorus (P), iron (Fe), nitrogen (N) and potassium (K) play a major role. Chemical fertilizers are in great demand as most soils are deficient in key nutrients. Hence efforts are made for an innovative, alternative and environmentally friendly techniques over conven-tional chemical fertilizers. Microbes play a pivotal role in increasing the nutrients bioavailability such as mobilization of major nutrients and nitrogen fixation that improve the plant yield and growth. In this review, current findings on the mechanisms utilized by various microbes will be discussed and highlighted. Furthermore, in improving soil fertility the inoculation of microbes in various forms such as sole inoculation, co-inoculation or in combination with organic fertilizer will be debated.
Keywords: Soil depletion, soil microbes, solubilization, co-inoculation, biofertilizer
1.1 Introduction
In developing countries from 1970 to 1995, the global food production had increased by 70% mainly because of new technology called conventional agriculture which was based on chemical fertilizers, synthetic pesticides and irrigation to produce high yields [1, 2]. The use of such technologies are destroying the natural environment in many ways such as surface and ground water contamination, increased pest resistance, soil erosion and reduced bio-diversity [3, 4]. Keeping in mind the increasing population and food demand worldwide, sustainable methods are key for food production. To avoid mitigating climate change and land degradation the sustainable methods must sustain this natural resource. This can be done by fine tuning of current technologies or to develop alternate technologies without
*Corresponding author: [email protected]
4 Soil Microenvironment for Bioremediation and Polymer Production
damaging the environment or natural resources to obtain high yield crops that can meet food demand globally.
About organic and inorganic fertilizers there are numerous myths [5, 6]. Without enough scientific evidence, it appears that mostly these myths are based on conjunctions, percep-tions, or for political motives. Regarding chemical fertilizers some legends are listed below:
1.1.1 Land and Soil Deterioration
Soil’s physical and chemical properties are destroyed by chemical fertilizers whereas fertility is improved by organic fertilizers [5]. Soil structure by chemical fertilisers is not affected if it is administered in the right quantity. Nitrogen (N) fertilizers tend to acidify soil to a pH of < 5 which can have adverse effects. If administered at an optimal dose it may posi-tively influence soil biota. If applied in high amount then it may alter soil texture, reduce in microbial community and increase soil acidification.
1.1.2 Micro-Nutrients Lacks
Regarding chemical fertilizers there is a popular misconception that macro-nutrients are in low amounts when in fact they are lacking. Organic fertilizers generally contain some micro-nutrients however there are some inorganic fertilizers containing micro-nutrients commercially available too [5].
Adoption of Integrated Soil Fertility management can help restore fertility of soil as explained by Vlek and Vielhauer [7]. This involves a strategy that allows for control of soil nutrients, nitrogen fixation and efficiency in administration.
This strategy encompasses use of biofertilizers which are biocompatible and economi-cally viable plant nutrients to help supplement synthetic fertilisers for a more sustainable agricultural system. The aim is to increase production and sustain balance of the nutrients in soil.
1.2 Biofertilizers
Microbial inoculants or biofertilizers are live or latent cell of strains that are efficient in phosphate solubilization, nitrogen fixation, potassium solubilization, siderophore produc-tion used for seed application, soil or composting areas where such microorganism popula-tion can increase and enhance several microbial processes to boost the nutrients availability that can be utilised by plants. The history of applying microbial inoculums have passed down generations of farmers. The efficacy of biofertilizers was evident when on small scale culture compost was introduced, it enhanced the decomposition of organic residues and agriculture by-products that resulted in healthy harvest of crops [8].
In biofertilizer making several things are considered such as growth profile of the selected microbe, organism’s optimum conditions and inoculum formulation. For the success of biological product critical steps are inocula formulation, application method and product storage.
Generally, six key steps are required in making a biofertilizer, 1) organism selection, 2) solation, 3) method selection and carrier material, 4) propagation method selection,
Applications of Microorganisms in Agriculture 5
5) prototype testing and 6) large scale testing. In late 1940’s, Malaysia started using indus-trial scale microbial inoculants and took guide by Brady rhizobium on legumes topped up in 1970’s. Malaysian Rubber Board (MRB), a government research institute has conducted research on Rhizobium inoculums for use on leguminous cover crops of young rubber trees in the large-scale plantations. Since 1980 many research projects on Mycorrhiza were con-ducted at University Putra Malaysia (UPM) and led to Azospirillum nitrogen to oil palm seedlings [8].
1.3 Rhizosphere
Root network is surrounded by a narrow zone of soil termed as rhizosphere [9], and the bacteria that colonises in the root environment are termed ‘rhizobacteria’ [10]. These roots not only provide mechanical support, nutrient uptake and facilitate water but also synthe-size various compounds [9]. Heterogeneous, multifaceted and active microbial communi-ties are attracted to the compounds produced by roots. In a nutshell they act as chemical attractants commonly called as root exudates. The chemical and physical properties of soil are modified by wide variety of chemical compounds (root exudate) and thus control the structure of the microbial community found in the proximate area of root surface [11]. Some microorganisms are attracted whereas some are repelled by the exudates. Exudate composition depends upon plant species, physiological state and surrounding microbes [12]. In addition, these exudates enhance symbiotic plant interaction and growth inhibi-tion to the hostile plant species [13, 14]. In the rhizosphere microbial activity also affects nutrient availability and root patterns thereby by modifying the quantity as well as quality of root exudates. Small organic molecule fractions derived by plants are metabolized fur-ther as nitrogen and carbon sources by microbes present in the vicinity. On the other hand, molecules obtained from microbes are regained by plants for growth and development [12]. Critical determinants of rhizosphere function are carbon fluxes. 5 to 15 percent of fixed car-bon is obtained through root exudation and transported to rhizosphere [15]. Any amount of soil associated or influenced by plants roots or their hairs as well as any plant produced materials encompass the rhizosphere [16]. Basically, rhizosphere can be grouped into three but interacting constituents a) rhizosphere (soil), b) rhizoplane (root surface), and c) root (itself). Rhizosphere is an area of soil which affects the microbial activity through the release of substrates by roots whereas rhizoplane is the root surface covered by soil particles and roots by microbes known as root colonization [17].
1.4 Plant Growth Promoting Bacteria
Plant growth promoting rhizobacteria (PGPR) are bacteria that colonise the rhizosphere. When PGPR are introduced to roots, seeds, or into soil either directly or indirectly they stimulate plant growth. They play an essential role in plant growth by increasing nutri-ent uptake, suppress plant pathogens and induce plant resistance to pathogens. The term PGPR was first coined by Kloepper and co-worker’s in the late 1970s [18]. PGPR are found widely in various genera such as Azospirillum, Agrobacterium, Acinetobacter, Arthrobacter, Bradyrhizobium, Bacillus, Burkholderia, Pantoea, Cellulomonas, Frankia, Rhizobium,
6 Soil Microenvironment for Bioremediation and Polymer Production
Thiobacillus, Pseudomonas, Serratia, Streptomyces. Rhizobacteria are most widely studied PGPR that colonizes the root surfaces and the rhizosphere [18, 19]. Some of these PGPR also enter root interior and establish endophytic populations as reviewed recently by Gray and Smith [19, 20].
Many of them can surpass the endodermis barrier and enter the vascular system by crossing the root cortex and bloom as endophytes in stem, tubers, leave and other parts [19, 21–23] Endophytic colonization is characteristic of PGPR (the attribute of selective adaptation to specific ecological niches) [19, 21], as a result friendly association between the host plant and bacteria is formed [21, 23] excluding any damage to the host plants [24–26].
1.4.1 Nitrogen Fixation
For plant growth and productivity nitrogen is one of the most important nutrients. Atmosphere is composed of 78% nitrogen but still not available to plants. Plants can only utilise atmospheric nitrogen when it is converted to ammonia, easily taken by plants by the process known as nitrogen fixation [27]. Enzyme nitrogenase produced by nitrogen fixing microorganisms converts the atmospheric nitrogen to ammonia [28, 29]. These nitrogen fixing microbes have symbiotic and non-symbiotic relationship with the plants. Members of Rhizobiaceae family have a symbiotic relationship with leguminous plants [30]. Free-living and endophytic forms of microorganisms are reported non symbiotic such as Azotobacter Cyanobacteria, Azospirillum [31].
As stated earlier symbiotic rhizobium nitrogen fixing rhizobacteria belong to family Rhizobiaceae (α-proteobacteria) and they create a symbiotic relation by infecting the roots of leguminous plants leading to a formation of a nodule. Rhizobia resides in the nodule as an intracellular symbiont [32]. Mesorhizobium, Sinorhizobium, Rhizobium, Azorhizobium and Bradyrhizobium, are together termed as Rhizobia. Diazotrophs, are non symbiont rhizobacteria that fix nitrogen in non leguminous plants and have a non-obligate rela-tion with the host plants [33]. Table 1.1, shows the most commonly studied bacteria for nitrogen fixation. The process of nitrogen fixation is carried out by an enzyme nitrogenase that carries out the process of nitrogen fixation. The complex enzyme structure consists of di nitrogenase reductase having iron as its cofactor and di nitrogenase having iron and molybdenum (Mo) as its cofactor [29]. Mo-nitrogenase, V-nitrogenase, and Fe nitroge-nase are three different reported nitrogen complexes based on the variation in the cofactor di nitrogenase [34, 35]. Nif genes carry out Nitrogen fixation in both symbiotic and free- living nitrogen-fixing microorganisms [36]. Formation and function of the enzyme require electron donation, iron protein activation, biosynthesis, Fe-Mo cofactor and regulatory
Table 1.1 Most common bacteria studied for nitrogen fixation.
Kinds Bacteria
Symbiotic Mesorhizobium, Sinorhizobium, Rhizobium,
Azorhizobium and Bradyrhizobium
Non-symbiotic Azotobacter, Beijerinckia, and Clostridium
Applications of Microorganisms in Agriculture 7
genes by Nif genes [37]. For nif gene expression oxygen is a negative regulator required for Rhizobium sp. bacteroid respiration [38]. The enzyme is kept active from oxygen as Bacterial leg haemoglobin with high affinity for oxygen. To pursue the process of nitrogen fixation efficiently oxygen supply to the bacteroid (for respiration) and nitrogenase enzyme complex prevention to oxygen should take place at the same time. To accomplish this task, simple way is to introduce bacterial haemoglobin through genetic engineering that binds the oxygen to the rhizobacteria [39]. This method was carried out through transformation by inserting haemoglobin gene of gram negative bacterium Vitreoscilla sp. to Rhizobium etli. Respiratory rate in rhizobial cells was two- to threefold higher as compared to the normal rhizobial cells [40]. Introducing the genes that produce haemoglobin from Vitreoscilla sp. to rhizobial cells started producing haemoglobin. So produced haemoglobin is transformed in the cell despite the low availability of oxygen which causes a strong affinity to oxygen. In bean plants significant 68% nitrogenase activity was observed when inoculated with trans-form rhizobium that showed leaf content was increased to 25-30% and 16% increase in the nitrogen content of the seeds [41].
It was reported that after the infection of legumes by Rhizobium sp. plants ethylene level was increased, and this increased ethylene concentration which helps in inhibiting the rhi-zobial infection and formation of nodules [42]. On roots of host legumes plant number of nodules formation can be increased by specific strains of rhizobia by synthesis of a small molecule termed “rhizobitoxine” that limit the increase in ethylene production [43]. It is a phytotoxin acts on the enzyme 1-aminocyclopropane-1-carboxylate (ACC) synthase that synthesizes ethylene [44]. ACC deaminase enzyme production has been reported by few rhizobial strains which removes some immediate precursor in plants before it translated to ethylene. The decrease in ethylene production leads to increase 25–40% biomass of the plant and nodule formation [45]. Naturally about 1-10% of rhizobial strain possess ACC deaminase and those strain that lack ACC deaminase genes, can gain this gene by intro-ducing it into the strain through genetic engineering [46]. The insertion of an deaminase ACC gene has been reported from Rhizobium leguminosarum bv.viciae into Sinorhizobium meliloti chromosomal DNA, 35% nodule number dramatically increased and 40% biomass alfalfa host plants as compared to control wild type strain [41, 46].
Azorhizobium, another strain of Rhizobia that not only forms nodules in stem and fixes nitrogen but also increases production of IAA indole acetic acid [47]. Another efficient nitro-gen fixer strain Bradyrhizobium when introduced in mucuna seeds results in increase nitrogen, total organic carbon, phosphorus and potassium contents in the soil. Hence increases plant biomass, growth, microbial population etc [48]. Non nodule- forming aerobic nitrogen-fixing bacteria Azospirillum from Spirilacae family are gram-negative [49]. Azospirillum halopraef-erens, Azospirillum amazonense, and Azospirillum brasilense are species from the same family whereas A. brasilense and A. lipoferum are major beneficial species [50]. Those plants hav-ing C4 dicarboxylic pathway (Hatch-Slack pathway) of photosynthesis Azospirillum form associative symbiosis with them as they use organic salts of malic and aspartic acid for their growth and nitrogen fixation [51].
Azotobacter belong to Azotobacteriaceae family, are free-living, aerobic, photoautotro-phic. They are found usually alkaline and neutral soil. Within this family Azotobacter chroo-coccum are the most common species [52]. Other species include, Azotobacter insignis, Azotobacter vinelandii, Azotobacter macrocytogenes, Azotobacter beijerinckii [50]. They secrete various phytochromes such as naphthalene acetic acid, gibberellins, vitamin B
8 Soil Microenvironment for Bioremediation and Polymer Production
complex and other substances that not only promote uptake of minerals, root growth but also inhibit certain root pathogens [53]. Azotobacter secrets special substance which also impsorves root growth, uptake of plants nutrients however it also prevents growth of spe-cific root pathogens [54, 55]. Antifungal antibiotics are produced by Azotobacter indicum another strain of Azotobacter inhibit the growth of few pathogenic fungi in the root region hence reduces the seed mortality [56]. In uncultivated soils and in rhizosphere zone of the crop plants Azotobacter population is generally very low and found in rhizosphere of several crop plants such as sugarcane, rice, bajra and vegetables [57]. Biofertilizers rich in Azolla provides nitrogen efficiently to rice plants as it decomposes in soil easily. In addition it plays a very important role in providing major amount of iron, zinc, phosphorus, molyb-denum, potassium and other micronutrients [58]. Prior to rice cultivation Azolla was used a green biofertilizer. In India most commonly used is Azolla pinnata and it can propagate by vegetative means on large commercial scale [59]. Azolla microphylla, Azolla caroliniana, Azolla filiculoides and Azolla mexicana species of Azolla are used in India for their large biomass production [50].
1.4.2 Phosphate Solubilization
Event though a large amount of Phosphorus is present in soil however its availability to plants especially crops is low [60]. The low availability of phosphorus due to its insoluble forms and is only absorbed by plants in two forms which are monobasic and the di basic ions [31]. In chemical fertilizers much of the soluble inorganic phosphorus becomes immo-bilized after application to the field. So, it becomes unavailable to plants and hence it is wasted [61].
Most bacteria found in the rhizosphere are phosphate solubilising, they produce organic acids and phosphatases which helps in the conversion of insoluble phosphorus to crop available forms. The nutrients availability is increased by phosphate solubilization in host plant by PGPR (most common mode of action) present in rhizosphere [62]. Successful inoculants strains are Rhizobium leguminosarum bv. Phaseoli with maize, for wheat Azotobacter chroococcum, B. circulans and Cladosporium herbarum, Enterobacter agglom-erans with tomato, Pseudomonas chlororaphis and P. putida with soybean, Rhizobium sp. and Bradyrhizobium japonicum with radish, Falvobacterium, Microbacterium, Bacillus, Burkholderia, Enterobacter, Beijerinckia, Erwinia, and Serratia [31, 63–68]. In soils and plant rhizosphere these zones particularly are rich in phosphate solubilizing bacteria includes both anaerobic and aerobic strains. In submerged soil aerobic strains are com-monly found. Youssef and Eissa [49] reported that phosphate solubilising bacteria are not generally found in non rhizospheric zone compared to rhizospheric zone. The phos-phate solubilization characteristic of rhizospheric bacterium by no means proves that it will function as a PGPR. Study of Cattelan et al. [68] showed that phosphate solubil-isation was observed in five isolates but only two promoted seedling growth. Similarly plant growth is also not increased by all phosphate solubilising PGPR. de Freitas et al. [68] isolated Bacillus sp. and from Canola rhizosphere Xanthomonas maltophilia (Brassica napus L.) positive for phosphate solubilization no change in phosphate content of the host plant though increase effect on plant growth was observed. Environmental factors (such as stress conditions) affects establishment and performances of the phosphate sol-ubilising bacteria [30].
Applications of Microorganisms in Agriculture 9
1.5 Microbial Mechanisms of Phosphate Solubilization
1.5.1 Organic Phosphate
Organic acids, protons, siderophores, carbon dioxide and hydroxyl ion production are the principal mechanisms observed by phosphate microbial organisms [69]. Upon chelation of cations with carboxyl and hydroxyl ions or pH reduction causes organic acid production that releases phosphate [70]; periplasmic space is the place where organic acids are pro-duced by the direct oxidation pathway [71].
1.5.1.1 Organic Acid Production
With the drop in pH, organic acids are secreted, the surroundings and the microbial cells are acidified that results in the release of phosphate by switching H+ for Ca2 [72]. Whereas it was observed that there is no direct correlation among amount of phosphate solubilisation and pH [73]. Therefore, the theory of H+ acidification was proposed by Illmer and Schinner, 1995 [74]. They found cation assimilation releases H+. Phosphate solubilisation is carried out by the assimilation of NH4 with H+ [75]. With the help of H+ translocation ATPase, H+ are released in the outer surface in exchange for cation uptake results in the production of organic acid mineral phosphate solubilisation [69]. Studies also show that phosphate solubilization can be carried without any organic acid production, within the microbial cell’s protons are release with the assimilation of NH4+ [75]. Among all the organic acid for phosphate solubilization gluconic acid is the most reported one, Figure 1.1, shows different types of acid produced by phosphate solubilising microbes The gluconic acid makes phos-phate available to plants through chelation of cations bounded to phosphate. Phosphate is also solubilised by gram negative bacteria by direct oxidation of glucose to gluconic acid [76]. Pyrroloquinoline quinone (PQQ) in phosphate solubilization acts as a redox cofactor in glucose dehydrogenases (GDH) [77].
Maloni acid
Glycolic acid
Glutamic acid
Maleic acid
Aspartic acid
Gluconic acid
Lactic acid
Succinic acid
Propionic acid
2-ketogluconic acidItaconic acid
Isovaleric acid
Isobutyric acid
Acetic acid
Oxalic acid
Citric acid
Malic acid
Glyoxalic acid
Fumaric acid
Tartaric acid
α-Ketobutyric acid
Figure 1.1 Various acid production by phosphate solubilising microbes. (Source: https://www.frontiersin.org/files/Articles/258916/fmicb-08-00971-HTML-r1/image_m/fmicb-08-00971-g002.jpg).
10 Soil Microenvironment for Bioremediation and Polymer Production
1.5.1.2 Inorganic Acid Production
Production of Inorganic acids (such as carbonic, nitric and sulphuric acids) and the pro-duction of chelating substances are also carried out by microorganisms for mineral phos-phate solubilization. Although inorganic acid and chelating substance effectiveness is found to be less than that of organic acids. Kim et al. [78] studied that in culture medium the increase in phosphate concentration is not solely because of organic production. Moreover, it is also observed that plant roots are extended effectively by Mycorrhizal fungi, results in increase soil volume through which phosphate may be absorbed [79].
1.5.1.3 Enzymes Production
Another mechanism reported in the literature for microbial phosphate solubilization is the release of enzymes or enzymolysis. In an experiment mechanism of phosphate solubiliza-tion was studied lecithin containing medium. Increased acidity was observed by an enzyme that produced choline by acting on lecithin [80]. Moreover, in liberating phosphorus, ester-ase types enzymes are involved. Phosphatase enzymes are known to produce by phosphate solubilizing microbes that helps in phosphate solubilization along with acids in aquatic environment [81].
1.5.2 Organic Phosphate Solubilization
Organic matter is a significant and a major source of organic phosphorus in soil. Organic phosphate in soil is present as inositol phosphate also called as soil phytate. Xenobiotic phosphonates are found in large amounts to be in detergents additive, flame retardants, pes-ticides and antibiotics, and are released regularly into the environment containing organic phosphates. As a compound are resistant to chemical hydrolysis because of their high molecular weight so there is need for bioconversion either to soluble ionic phosphate (Pi, HPO42-, H2PO4-), or low molecular-weight organic phosphate, to be absorbed by microbial cells [82]. Halvorson et al. [83] proposed one important theory called as ‘sink theory’ for the solubilisation of organic phosphorus.
Phosphorus is continues removed by Ca-P compound dissolution. In the biomass of phosphate solubilizing microbes Phosphorus content is correlated to the decomposi-tion of phosphorus in organic substrates [84]. Microbes play a vital role in phosphorus cycle; various enzymes are involved. Enzymes that dephosphorylate the phosphor-ester or phosphoanhydride bond of organic compounds, are non-specific acid phosphatases. Phosphomonoesterases is an example of non-specific acid phosphatases (NSAPs) is the most studied enzyme produced by phosphate solubilizing microbes [85]. These enzymes can be acid or alkaline in nature [86]. The soil pH ranges from acidic to neutral values mostly where phosphatase activities occur. In this process it shows that acid phosphatase plays a vital role [87]. In production of organic phosphorus, phytase is an enzyme produced by phosphate solubilizing microbes. Phytase releases phosphorus in soil from organic mate-rials such as pollen and seeds of plants that are deposited in phytate form. This phytate is degraded by phytase enzyme and phosphorus is released and available for plant use. The phosphate solubilizing microbes play an important in the availability of phosphorus to plants as plants generally cannot take phosphorus directly from phytate [88].