Microbial polysaccharides

Polysaccharides produced by microorganism during their growth and especially at the stationary phase of growth when there is excess of carbon source in the medium.
High molecular weight carbohydrate polymers mainly produced by bacteria and fungi.
Microbial polysaccharides are of two types:
Storage polysaccharides like glycogen, inulin etc.
Exopolysaccarides like xanthans, dextrans, levans which are secreted by the cells.

1. Microbial Polysaccharides
Xanthan, Dextran, Pullulan

2. Introduction
•Polysaccharidesproducedbymicroorganismduringtheirgrowthand
especiallyatthestationaryphaseofgrowthwhenthereisexcessof
carbonsourceinthemedium.
•Highmolecularweightcarbohydratepolymersmainlyproducedby
bacteriaandfungi.
•Microbialpolysaccharidesareoftwotypes:
1.Storagepolysaccharideslikeglycogen,inulinetc.
2.Exopolysaccarideslikexanthans,dextrans,levanswhichare
secretedbythecells.

3. TypesofPolysaccharidesonthebasisof
theirfunction
•Capsularpolysaccharides:giveprotectionagainstimmunesystem
andserveasphysicalbarriertoinfectionsbybacteriophages.
•Polysaccharidesheath:retainwaterandpreventdehydrationofcells
underadverseconditions.
•Extracellularpolysaccharides:usedtobindmicroorganismsto
varioussurfaces(biofilmformation).
•Lipopolysaccharides:attachedtooutermembraneofGramnegative
bacteriadetermineimmunogenicproperties.

4. Xanthan Production

5. Introduction
•XanthanisthemostwidelyusedindustrialExopolysaccharide(EPS)
producedbyfermentationofglucose/sucrose.
•XanthanisproducedbybacteriumXanthomonascampestris.
•Itissolubleincoldwaterandexhibitshighpseudo-plasticflow.
•Genusxanthomonasbelongstoproteobacteriaandconsistsofplant
pathogens.
•Theyaremotile,aerobic,Gramnegativerodsandgenerallyproduce
yellowpigmentsduringgrowth.

6. Xanthomonascampestris
•Thisisbacterialspeciesthatcausesavarietyofplantdiseases.
•Thesebacteriaarecommonlyfoundontheleavesofbrassica
vegetablessuchascabbage.
•Xanthomonascampestriscausesblackrotinplantsbelongtogenus
Brassica(cabbage,cauliflower,Brusselsprouts,broccoli,rutabaga,
turnipsetc.)
•Thisbacteriaproducespolysaccharideatitscellwallsurfaceduringits
normalcellcyclebyacomplexenzymaticprocesses.
•Itisusedforcommercialproductionofxanthangumthatisan
efficientviscosifierofwaterandhasimportantusesinfoodindustry.

7. Xanthomonascampestris
Leaf spot of English Evy Black spot on cabbage leaf

8. Production
•Awellaeratedmediumcontainingnitrogensource,glucoseand
varioustraceelementsischoseninsubmergedfermentation.Corn
syrupisalsochosensometimes.
•MediumisinoculatedbyXanthomonascampestris.
•Duringfermentation,thepHofthemediumisdecreasedduetothe
formationofmetabolicacids.
•XanthangumalsoahsacidicfunctionsbutifthepHreachesacritical
pointlike5.0,thegumproductiondecreasesdrastically.
•AnearlyneutralpHallowsthegumsynthesistocontinueuntilallthe
carbohydratesubstrategetsutilizedandthefermentationiscomplete.

9. •Afterfewdays,bacteriautilizeallthecarbohydrateinthemediumand
producexanthangum.
•Afterthefermentation,brothifheatedtokillbacteriaandxanthangum
isrecoveredbyprecipitationwithisopropylalcohol.Therecovered
xanthangumisthendehydratedandisdried,milledandfinally
packed.

10. Applications
•Used in toothpaste and hard rock oil drilling.
•As food additives to thicken, emulsify and stabilize water-based foods.
It is used in salad dressings, sauces, condiments, ice creams and other
frozen foods.
•In gluten free baking products.

11. Dextran Production

12. Introduction
•Dextranishomopolymerofglucoseunitscontainingmainlytwo
differentlinkagesα1-4andβ1-3withamolecularmassof15to500
kDa.
•ProducedbyvarietyofGrampositiveandGramnegativebacteria
includingNeuconostocmesenteroidsandStreptococcusspecies.
•Forindustrialproduction,Neuconostocmesenteroidsisused.
•Itisthefirstmicrobialpolysaccharidetoreceiveapprovalforfooduse.

13. Production
•DextranisproducedbyLeuconostocmesenteroidsfromsucroseby
extra-cellularenzymedextransucrase,whichactsonsucrose,
polymerizingtheglucoseunitsandliberatingfreefructoseinthe
medium.
•Fructosemoleculesareutilizedforenergyandgrowth.
Sucrose Polymerization of glucose Free Fructose
dextransucrase
Energy & Growth

14. Production
•Dextranisproducedatindustrialscalebysucroserichmedia.
•Fermentationmediaconsistsof:
oLeuconostocmesenteroides
o15%sucrose
opH7.0
o20hoursincubation
o30°C
•Afterincubation,culturemediumprecipitatedusingequalvolumeofchilled
ethanol,shakenvigorouslyat10,000rpmfor15minutes.
•Supernatantisdecanted.Steprepeatedtwice.
•Precipitateddextrandriedundervacuumovercalciumchlorideat30°C.

15. Applications
•Inwounddressingstoabsorbfluid(drydextranhaveveryhighwater
regainingcapacity).
•Asbloodplasmaexpander,forpreventionofthrombosisduringWorld
War-II.
oThrombosis:bloodclotindeepvein,usuallyinlegs
oPlasmaexpander:Hypertonicfluidsthatincreasecirculatingbloodvolume
throughinfluxofinterstitialfluidbyincreasingosmoticpressure.
Blood Vessel
Interstitial fluid
Increase
Osmotic Pressure
influx
Dextran

16. •Infoodindustry,asthickenerforjamandicecream:prevents
crystallizationofsugar,improvesmoistureretention,maintainflavor
andappearanceoffoodstuffs
•Asanticoagulantandantiviralagent
•Dentalcariescausingbacterium,Streptococcusmutansusesthe
dextrantostronglyholdtheteeth.Dextranasesintoothpastesdissolve
thedextrananddislodgesthebacterium.
•Inpaperproducts,oildrillingandsoilconditioners.

17. Pullulan Production

18. Introduction
•Pullulanisawatersoluble,neutralglucanproducedextracellularly.
•Pullulanisapolysaccharidepolymerconsistingofmaltotrioseunits,
alsoknownasα-1,4-;α-1,6-glucan'.Threeglucoseunitsinmaltotriose
areconnectedbyanα-1,4glycosidicbond,whereasconsecutive
maltotrioseunitsareconnectedtoeachotherbyanα-1,6glycosidic
bond.

19. Production
•Itiscommerciallyproducedbyaerobicallygrowingtheblackyeastlike
fungusAureobasidiumpullulans.
•Aureobasidiumpullulansiswellknownasanaturallyoccurringepiphyteor
endophyteofawiderangeofplantspecies(e.g.apple,grape,cucumber,
greenbeans,cabbage)withoutcausinganysymptomsofdisease.
•Pullulanisproducedassecondarymetaboliteinthelateexponentialand
earlystationaryphasesofgrowthand70%ofsubstrate(glucose)is
convertedtopolysaccharide.
•Molecularweightsofpullulansrangefromthousandsto2000kDa
dependingonthegrowthconditionsofthefungus.
•Thefermentationisrelativelyslow(5days)comparedwiththeproduction
ofbacterialexopolysaccharides.

20. Applications
•Nonionicpolysaccharidewithmaydesiredpropertiessuchasblood
compatibility,biodegradability,non-toxic,non-immunogenic,on-
mutagenicandnon-carcinogenic.
•Infoodindustryasdietaryfiberandreplacesstarchinbakery
products.
•Alsousedinsauceandbeverages.
•Pullulanisafilmformerandbinderpopularintheproductionof
breathfresheningstrips.
•Inbiomedicalareafordrugdeliverysuchasinsulin.
•Resemblesnylonorrayonandalsousedinpapermanufacture.