EXTRACELLULAR EXTRACELLULAR POLYSACCHARIDESPOLYSACCHARIDES

Course TeacherDr. R.VELAZHAHAN

StudentMOHAMMED FAISAL P

SYNOPSIS

INTRODUCTION

EPS CHEMISTRY

EPS PRODUCED BY PATHOGENS AND THEIR ROLES

CONCLUSION

INTRODUCTIONINTRODUCTION

Several microorganism - mucilaginous substances that coat their bodies and provide the interface between the outer surface of the microorganism and its environment.

EPS appear to be necessary for several pathogens to cause normal disease symptoms

Directly responsible for inducing symptoms or by indirectly facilitating pathogenesis by promoting colonization or by enhancing survival of the pathogen.

EPS are complex mixture of high molecular weight polymers (Mw > 10,000), are excreted by microorganisms via lysis and hydrolysis.

They can protect the cells from the harsh external environment and provide with energy and carbon source when substrate is in short supply

(Wingender et al. 1999)

The origin of EPS is very complex, and their components and content heavily depend on many factors, such as bacterial type, cultivation time, substrate, and growth state (attached or suspended), etc.

(Sheng and Yu 2006)

Polysaccharides can be divided into 3 main groups - Intracellular polysaccharides inside, or as part of, the cytoplasmic -cell-wall polysaccharides a structural part of the cell wall - extra- cellular polysaccharides located outside the cell

Extracellular polysaccharides occur in two forms:

1. Loose slime which is non adherent to the cell. 2. Microcapsules and capsules which adhere to the cell wall

BIOSYNTHESIS OF EPS - XANTHAN

PROPERTIES OF EPS

2 important properties

1. Capsular polysaccharides are highly hydrated – protection in dessication and prevents hydrophobic molecules from penetrating the capsule.

2. Acidic EPSs produced by most plant pathogenic bacteria are highly anionic – acts as ion exchange resins

(Ferris and Beveridge, 1985)

Chemistry

Polysaccharides fall into two groups according to the number of component sugars present.

homopolysaccharides or homoglycans in which there is only one component sugar and simple straight chain polymer of the disaccharide acetylhyalobiuronic acid

heteropolysaccharides or heteroglycon in which there are two or more component sugar

The structure and synthesis of the acidic heteropolysaccharide capsules produced by enteric bacteria and xanthomonads are much more complex

Most of what is known about the synthesis of bacteria capsular heteropolysaccharides comes from the studies of cell free enzymes of Xanthomonas

Heteropolysaccharide

ROLE OF EPS

EPSs - Produced by most bacteria, including many plant pathogensSecreted as a loose slime or as capsular material.EPSs - to protect free-living bacteria from a variety of environmental stresses.It may aid pathogenesis -sustaining water-soaking of intercellular spaces, -altering the accessibility of antimicrobial compounds -defense-activating signals - blocking the xylem and thereby producing wilt symptoms (Denny, 1995)

EPS IN PLANT PATHOGEN INTERACTION

In the bacterial wilt of solanaceous crops caused by Ralstonia solanacearum, EPS1 is the main virulence factor of the disease.

EPS1 is a polymer composed of a trimeric repeat unit consisting of

N- acetyl galactosamine, deoxy-l-galacturonic acid, and trideoxy-d-glucose.

At least 12 genes are involved in EPS1 biosynthesis

EPS 1 - Ralstonia solanacearum

EPS1 is produced by the bacterium in massive amounts and makes up more than 90% of the total polysaccharide.

EPS likely causes wilt by occluding the xylem vessels and by causing them to rupture from the high osmotic pressure.

Xanthan gum of Xcc provide the most complete model for EPS synthesis

Xanthan gum is a pentasaccharide composed of two glucose (Glu), one glucuronic acid (Glc A) and two mannose (Man) moieties.

Glu froms a beta 1,4 linked backbone, and a Man – Glu A- Man resiudes in the side chain are acetylated and pyruvylated in specfic, alternating pattern

Xanthan Gum – Xanthomonas campestris pv. campestris

Sturcture of xanthan gum bacterial wilt of crucifers

Amylovorin - Erwinia amylovora

E. amylovora -rapid blighting of blossoms and vegetative shoots of susceptible plants.

The first symptoms of the disease (fire blight) are water-soaking and wilting of affected tissues; necrosis follows.

Amylovorin – high molecular weight polysaccharide-host specific toxinIncreased permiability of cell membrane to solutes Polysaccharides and glycopeptides induce wilting by either disrupting membrane semi permeability or physically restricting water movement

Genes encoding the biosynthesis of amylovorin are contained within a 12-gene operon on the E. amylovora chromosome, and insertional mutants of critical genes of the operon result in a loss of pathogenicity

(Bellemann and Geider 1992)

E. amylovora also produces levan, a homopolymer of fructose residues that is produced following the breakdown of sucrose.

Levan production is controlled by the lsc gene encoding the levansucrase enzyme, and also contributes to virulence.

(Geier and Geider 1993)

STEWART’S WILT OF CORN

Pantoea stewartii subsp. stewartii is the causal agent of Stewart's wilt and blight of corn and is transmitted by the corn flea beetle.

Stewartan is of high molecular weight (45 X 106 Da)

Pathogenicity of P. stewartii is related to the production of extracellular polysaccharides that contribute to occlusion (plugging) of xylem vessels and symptom development.

Structure of the repeating units of stewartan as derived

from NMR spectra

The obvious mucoid nature of many C. michiganensis ssp. sepodonicum was found to produce an extracellular “glycopeptide” which is actually an EPS

EPS induces wilt symptoms by interfering with water transport

Denny (1996)

RING ROT OF POTATO

Novel techniques in the study of specific polysaccharides

Recent progress in the surface and structure analysis of extracellular polysaccharides has resulted from the development of advanced microscopy and spectroscopy techniques,

Atomic force microscopy (AFM)Confocal laser scanning microscopy (CLSM)Infrared spectroscopyNuclear magnetic resonance imaging (NMRI)Raman spectroscopy (RM) and scanning electron microscopy (SEM)

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