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Unformatted text preview: Vol. 57,No. 11 DifferentialFermentation ofCellulose Allomorphs by Ruminal Cellulolytic Bacteria P. J. WEIMER,l .* A. D. FRENCH,3 AND T. A. CALAMARI, JR.3 U.S. DairyForage Research Center, AgriculturalResearch Service, U.S. Department ofAgriculture,1 and Department of Bacteriology, University ofWisconsin-Madison,2 Madison, Wisconsin 53706, and Southern Regional Research Center, AgriculturalResearch Service, U.S. Department ofAgriculture, New Orleans, Louisiana 701793 Received 10June 1991/Accepted 20August 1991 In addition to itsusual nativecrystalline form (cellulose I),cellulose can exist in a variety ofalternative crystallineforms(allomorphs)whichdifferintheirunitcelldimensions,chainpackingschemes, and hydrogen bonding relationships. We prepared, by variouschemical treatments, four different alternative allomorphs, along with an amorphous (noncrystalline) cellulosewhich retained itsoriginal molecular weight. We then examinedthekineticsofdegradationofthesematerialsbytwo speciesofruminalbacteriaand by inoculafrom two bovine rumens. Ruminococcusflavefaciens FD-1 and Fibrobacter succinogenes S85 were similar to one anotherintheirrelativeratesofdigestionofthedifferentcelluloses, which proceeded inthefollowingorder: amorphous > 1111 > IV, > 11111 > I > II. UnlikeF. succinogenes, R.flavefaciensdidnot degrade cellulose II, even after an incubation of3 weeks. Comparisons ofthe structural featuresofthese allomorphs with their digestionkineticssuggestthatdegradation isenhanced by skewing ofadjacent sheetsinthemicrofibril,but is inhibitedbyintersheethydrogen bonding and byantiparallelisminadjacentsheets.Mixed microflorafromthe bovinerumens showed invitrodigestionratesquitedifferentfromone another and from thoseofboth ofthe two pure bacterialcultures,suggestingthatR.flavefaciensandF. succinogenes(purportedly a m o n g themost activeofthecellulolyticbacteriaintherumen) eitherbehavedifferentlyintheruminalecosystem fromthe w a y theydo inpure cultureor didnot playa major roleincellulosedigestionintheseruminal samples. Cellulose is one of the most abundant biopolymers on earthandisthechiefstructuralcomponent ofplantcellwall materials. Itthusisa majorcontributortotheglobalcarbon cycle, and its biodegradation supports a large number of spetmicroorganisms. Research on cellulose biodegra- dation has been heavily oriented toward studies on the physiological characteristics ofcellulolytic microorganisms andthebiochemicalpropertiesoftheircellulolyticenzymes. Although cellulose isarranged invariable and often highly complexways withinplantmaterial,relativelylittleattention has been paid to the relationship between this "fine structure"ofcelluloseand itsbiodegradation.Itdoesappear that fine-structural features such as crystallinity, surface area, and pore structure have variable effectson the rate or extent ofbiodegradation by differentclasses ofcellulolytic microbes (4)....
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