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Fermentation Of Cellulosic Substrates In Batch And Continuous Culture By Clostridium Thermocellum, Lee R. Lynd, Hans E. Grethlein, Richard H. Wolkin
Fermentation Of Cellulosic Substrates In Batch And Continuous Culture By Clostridium Thermocellum, Lee R. Lynd, Hans E. Grethlein, Richard H. Wolkin
Dartmouth Scholarship
Fermentation of dilute-acid-pretreated mixed hardwood and Avicel by Clostridium thermocellum was comparedinbatchandcontinuouscultures.Maximumspecificgrowthratesper hourobtainedon cellulosic substrateswere 0.1inbatchcultureand>0.13incontinuousculture.Cellyields(gramsofcellsper gram of substrate)inbatchculturewere 0.17forpretreatedwoodand0.15forAvicel.Ethanolandacetatewere the mainproductsobservedunderalconditions.Ethanol:acetateratios(ingrams)were approximately1.8:1in batchcultureand generallyslightlylessthan 1:1incontinuousculture.Utilizationofcellulosicsubstrateswas essentially complete in batch culture. A prolonged lag phase was initialy observed in batch culture on pretreated wood; the length of the lag phase could be shortened by addition of cell-free spent medium. In continuousculturewith-5g ofglucoseequivalentper literinthefeed,substrateconversionrelativeto theoreticalrangedfrom0.86ata dilutionrate(D)of0.05/hto0.48ata D of0.167/hforAvicelandfrom0.75 ata D of0.05/hto0.43ata D of0.11/hforpretreatedwood.Atfeedconcentrationsof<4.5g ofglucose equivalentperliter,conversionofpretreatedwoodwas80to90%atD= 0.083/h.Lowerconversionwas obtainedathigherfeedsubstrateconcentrations,consistentwitha limitingfactorotherthancellulose.Free Avicelaseactivitiesof12to84mU/mlwere observed,withactivityincreasinginthisorder:batchceliobiose, batchpretreatedwood< batchAvicel,continuouspretreatedwood< continuousAvicel.Freecellulaseactivity was higheratincreasingextentsofsubstrateutilizationforbothpretreatedwoodandAvicelunderal conditions tested. The results indicate that fermentation parameters, with the exception of free cellulase activity,are essentiallythesame forpretreatedmixedhardwoodandAvicelundera varietyofconditions. HydrolysisyieldsobtainedwithC.thermocellumcellulaseactingeitherinvitroor invivowere comparableto thosepreviouslyreportedforTrichodermareeseion thesame substrates.
Fermentation of dilute-acid-pretreated mixed hardwood and Avicel by Clostridium thermocellum was comparedinbatchandcontinuouscultures.Maximumspecificgrowthratesper hourobtainedon cellulosic substrateswere 0.1inbatchcultureand>0.13incontinuousculture.Cellyields(gramsofcellsper gram of substrate)inbatchculturewere 0.17forpretreatedwoodand0.15forAvicel.Ethanolandacetatewere the mainproductsobservedunderalconditions.Ethanol:acetateratios(ingrams)were approximately1.8:1in batchcultureand generallyslightlylessthan 1:1incontinuousculture.Utilizationofcellulosicsubstrateswas …
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