Life Sciences Commons^™

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 …

Microbiological Immunocytochemistry: A Review Of Current Trends And Applications, Julian E. Beesley

Scanning Microscopy

It has been considered worthwhile to update previous reviews of microbiological immunocytochemistry in order to identify areas of current importance in this continually expanding area of research. Publications in virology, bacteriology and protozoology indicate a continued interest in immunocytochemistry. Deployment of colloidal gold techniques is almost universal in these applications. The post-embedding technique was the most widely applied technique although a few studies employed the immunonegative stain, pre-embedding and immunoreplica techniques, thereby reflecting the use of colloidal gold in all other areas of the biological sciences.

An Electrochemical Method Of Measuring The Oxidation Rate Of Ferrous To Ferric Iron With Oxygen In The Presence Of Thiobacillus Ferrooxidans, David J. Oliver, B. Pesic, P. Wichlacz

David J. Oliver

The oxidation of Fe2+ with oxygen in sulfate solutions was studied in the presence of T. ferrooxidans. To measure the chemical activity of bacteria, and the oxidation rate of iron, the redox potentials of solutions were continuously monitored during the experiments. The redox potentials were simultaneously monitored on the platinum and pyrite indicator electrodes. The redox potential versus time curves were further used to calculate the basic kinetic parameters, such as the reaction orders, the activation energy, and the frequency factor. It was found that under atmospheric conditions, and at Fe2+ < 0.001M, T < 25°C, and at pH above 2.2, the oxidation of iron is governed by the following rate expression: [equation image] Below pH = 2.2, the oxidation rate is independent of H+ Concentration.

Effect Of Electrical Charge On Attachment Of Salmonella Typhimurium To Meat Surfaces, James S. Dickson, John D. Crouse

James S. Dickson

Treating tissue with electrical current was found to affect both the initial attachment and total numbers of attached Salmonella typhimun’unl to meat tissues. When lean tissue was attached to the positive terminal of the power supply operating at 50 volts/125 mA DC, the total numbero f attachedc ells increasedT. hcrc was no effect when the samples were attached to the negative terminal. There was a significant (PcO.05) effect on the percentage of strongly attached bacteria with an increase in treating time. Electrical current was found to increase the percentage of strongly attached cells immediately after the current was applied.

Algorithm To Estimate Cell Biovolume Using Image Analyzed Microscopy, Me Sieracki, Cl Viles, Kl Webb

VIMS Articles

This paper describes an algorithm for calculating the biovolume of cells with simple shapes, such as bacteria, flagellates, and simple ciliates, from a 2-dimensional digital image. The method can be adapted to any image analysis system which allows access to the binary cell image-( i.e., the pixels, or (x,y) points, composing the cell. The cell image is rotated to a standard orientation (horizontal), inand a solid of revolution is calculated by digital integration. Verification and a critical assessment of the method are presented. The algorithm accounts for irregularities in cell shape that conventional methods based on length, width, and geometrical …

Protoporphyrinogen Oxidation, A Step In Heme Synthesis In Soybean Root Nodules And Free-Living Rhizobia., Nicholas J. Jacobs, Susan E. Borotz, Mary Lou Guerinot

Dartmouth Scholarship

Extracts of the crude bacteroid fraction of symbiotically grown Bradyrhizobium japonicum were much more active in oxidizing protoporphyrinogen to protoporphyrin than were extracts of cells grown under free-living conditions, especially when assayed in atmospheres containing only traces of oxygen. This correlates with the higher heme content of the microaerophilic nodules. Furthermore, the high level of oxidative activity in the crude bacteroid fraction was associated with an uncharacterized membrane fraction, probably of plant origin, that was separable from the bacteroids by Percoll gradient centrifugation.