MICROBIOLOGYROLE OF MICROORGANISMS IN

BIOABSORBTION OF METALS

FROM DIFFERENT ENVIRONMENTS AND ITS BENEFITS AND LIMITATIONS.

BIOABSORPTIONTHE MECHANISM OF BIOSORPTION OF METALS BY MICROBESFUNGI ,ALGAE,BACTERIA IN BIOABSORPTION FACTORS AND LIMITATION S COMMON AND INDUSTRIAL USEBIOABSORPTION OF METALS FROM DIFFERENT ENVIRONMENTSNATURAL OCCURANCE OF METALS AND MICROBES CONCLUSION

INTRODUCTION discharge of heavy metals into ecosystems, a matter of concern pollutants include Pb, Cr, Hg, U, selenium, Zn, Ar, Cd, Ag, Au, Cu and Ni.

mining operations, refining ores, sludge disposal, fly ash from incinerators, processing of radioactive materials, metal plating, or the manufacture of electrical equipment, paints, alloys, batteries, pesticides or preservatives.

Heavy metals Zn, pb , Cr ,number of applications in engineering works, paper and pulp industries, leather tanning, organochemicals, petrochemicals fertilizers,

In immobilized form in sediments & as ores , by human activities the biogeochemical cycles are disrupted increasing of heavy metals in environment.

without proper treatment poses significant threat to environment & health, due to biodegradable and persistent nature

biomagnification, accumulate in food chains Other processes ,inefficient.e.g chemical

precipitation, Phytoremediation, Ion-exchange, Ultrafiltration, Electrodialysis

Think tank?..…

So what is the possible solution then,which is efficient,does nt produce toxic sludge,isnt time consuming ,economical &

environmental friendly?

safer process of metal absorption by by microbes…..

.

BIOABSORPTION Metal removal / recovery methods ,based on

sequestering properties of microbes

microbial mass removes higher metal ions by “passive” sorption or complexation.

metabolically passive process,does’nt require energy,

higher in dead cells than living cells.

major advantages

• • Low cost; • • High efficiency;• • Minimisation of chemical and or biological

sludge; • • No additional nutrient requirement; • • Regeneration of biosorbent;• Possibility of metal recovery.

How does it take place? Bioabsorbents are prepared from naturally abundant or waste biomass of

algae, fungi, moss or bacteria that have been killed..

a rapid passive metal sequestration by the non-growing biomass

involves mechanisms like ion exchange, chelation, complexation inorganic precipitation may occur by hydrolysis and inorganic deposition via adsorption by physical forces and ion entrapment in inter and intra-fibrillar capillaries and spaces of the structural polysaccharide network as a result of diffusion through cell walls and membranes

.active groups of cell constituents like acetamide group of chitin, structural polysaccharides of fungi amine, sulphahydral and carboxyl group in protein, phosphodiester (teichoic acid), phosphate, hydroxyl in polysaccharides participate

a variety of process physicochemical and biological

According to the dependence on the cell's metabolism, biosorption mechanisms can be divided into:

1. Metabolism dependent and 2. Non -metabolism dependent. According to the location where metal

removed from solution is found, biosorption can be classified as

1. Extra cellular accumulation/ precipitation 2. Cell surface sorption/ precipitation and 3. Intracellular accumulation.

Method involved

• Physical adsorption• Ion Exchange• Complexation• Precipitation• Use of Recombinant bacteria for metal

removal

metal biosorbents •Algae,• bacteria • fungi • yeasts

Biosorption by Fungi

a high percentage of cell wall material Cell walls of fungi present a multi-laminate

architecture where up to 90% of their dry mass consists of amino or non-amino polysaccharides, shows excellent metal binding properties

Rhizopus, Aspergillus, Streptoverticillum and Saccharomyces are fungi used.

fungi show filamentous or hyphal growth

Saccharomyces cerevisiae can remove toxic metals, recover precious metals & clean radio-nuclides from aqueous sols to various extents.

S. cerevisiae is a product of many single cell & alcohol fermentations,

can be procured in large quantity at low cost. Saccharomyces differentiates b/w different metals

such as selenium, antimony and mercury based on their toxicity.

property makes S. cerevisiae useful in analytical measurements FungiMetal adsorbed

Phanerochaete chrysosporium

NI(11),Pb(11)

Aspergeillus nigerCdAspergillus fumigatesUr(vi)Aspergillus terreusCuPenicillium chrysogenum

Au

Biosorption by algae and moss low nutrient requirements, being autotrophic

produce a large biomass, unlike microbes, do not produce toxic substances. Binding of metal ions on algal surface depends on

different conditions Mechanisms such as entrapment of metal both in the

form of insoluble micro deposits in the inter and intra-fibrillar capillaries can contribute to the metal binding.

The photoautotrophs, eukaryotic algae cell wall are mainly cellulosic and potential metal binding groups

amino & carboxyl grps ,nitrogen /oxygen of the peptide bonds are for coordination bonding with metal ions such as lead (II), copper (II) and chromium (IV

Algae

Chlorella emersonii cd Sargassum muticum Cd Ascophyllum sargassum Pd cd Ulva reticulate Cu(11brown sea weeds CrEcklonia species Cu(11)

Biosorption by bacteria

Bacillus sp. has been identified as having a high potential of metal sequestration and has been used in commercial biosorbent preparation.

Pseudomonas sp. Zoogloea ramigera and Streptomyces sp

. Bacterial resistance to heavy metals is conferred by specific resistance determinants, which are often, but not always, carried on plasmids

Cell wall of gramnegative bacteria is not heavily cross-linked.

They have an outer membrane which is composed of an outer layer of lipopolysaccharides (LPS), phospholipids and proteins

. Gramnegative bacteria are more widespread in metal contaminated soils then gram-positive bacteria.

The anionic nature of bacterial surface enables them to bind metal cations through electrostatic interactions. Because of their thickness and anionic character which is mainly due to peptidoglycan, teiochoic acid and teichuronic acids the cell wall of gram positive bacteria has high capacity for metal binding

. Bacillus subtilis, B. licheniformis, Pseudomonas sp., Serratia mercascens, Pseudomonas aeruginosa, Zooglea ramigera and Streptomyces sp. are widely used for metal removal from effluent

EXAMPLES FROM RESEARCH: CROMIMUM Polysulphone immobilized Rhizopus nigricans were subjected to Cr (VI) recovery

experiments using 0.01 N solutions of mineral acids, salt solutions, alkalies, deionised distilled water and buffer solutions.

IRON ,CALCIUM ,NICKLE A few experiments were conducted to desorb the metal ions from the loaded

waste fungal biomass of Aspergillus ,as a function of HCl concentration in the case of iron, calcium and nickel. The results revealed that with increase in HCl concentrations, the desorption of the metal ions increased and at 5M HCI, complete removal of calcium and iron would be achieved while about 78% Nickel would be desorbed.

MERCURY The desorption of the adsorbed Hg (II) from the biosorbent - immobilized and

heat inactivated Trametes versicolor and Pleurotus sajur-caju were studied in a batch system (Arica et al. 2003). Hg (II) ions adsorbed onto the biosorbents were eluted with 10 mmol dm-3 HCl and the results showed that more than 97% of the adsorbed Hg (II) ions were desorbed from the biosorbents.

Factors affecting/limitation:

• Effect of temperature

• Effect of pH

• Biomass concentration

• Size of bioabsorbent

• Inorganic salts

• Biorectors in bioabsorption

• Biosorption by immobilized cells

• Adsorption on inert supports

• Desorption:

CONCLUSION

Widespread of pollution due to humans . A number of organic pollutants, are resistant to

degradation and represent an ongoing toxicological threat to both wildlife and human beings.

A number of organic pollutants, are resistant to degradation and represent an ongoing toxicological threat to both wildlife and human beings.

some of the microbial interactions with metals are industrially exploited or at least have a technological potential for such exploitation.

• Despite the fact that the technology also suffers inherent disadvantages like early saturation of biomass, little bio logical control over the characteristics of biosorbents.

• It offers several advantages including cost effectiveness, high efficiency, minimization of chemical/biological sludge, and regeneration of biosorbent with possibility of metal recovery.

• In countries, with the rush for rapid industrial development coupled with lack of awareness about metal toxicity there is an urgent need for developing an economical and eco-friendly technology which satisfies these demands when other conventional methods fail.

BIOABSORPTION OF HEAVY METAL

DIFFERENT ENVIRONMENTS