Bacterial conversion of glycerol to beta-hydroxypropionaldehyde

beta-hydroxypropionaldehyde (3-HPA) can be oxidized to acrylic acid, an industrially important chemical used in the manufacture of synthetic plastics and other polymers. Of 19 genera and 55 strains tested, 3 Klebsiella and 2 Enterobacter strains produced 3-HPA. The most efficient strain was Klebsiella pneumoniae NRRL B-4011. Under optimum conditions (28 degrees C; 40 g of semicarbazide hydrochloride per liter, 70 g of glycerol per liter; and pH 6.0), 3.1 g of B-4011 cells per liter accumulated 22 g of 3-HPA per liter at a specific rate of 0.83 g/g per h; however, 14.5 g of cells per liter accumulated 46 g of 3-HPA per liter at a specific rate of 0.41 g/g per h.     

Fermentation of xylans by Butyrivibrio fibrisolvens and other ruminal bacteria

The ability of Butyrivibrio fibrisolvens and other ruminal bacteria (6 species, 18 strains) to ferment a crude xylan from wheat straw or to ferment xylans from larchwood or oat spelts was studied. Liquid cultures were monitored for carbohydrate utilization, cell growth (protein), and fermentation acid production. B. fibrisolvens 49, H17c, AcTF2, and D1 grew almost as well on one or more of the xylans as they did on cellobiose-maltose. B. fibrisolvens 12, R28, A38, X10C34, ARD22a, and X6C61 exhibited moderate growth on xylans. Partial fermentation of xylans was observed with Bacteroides ruminicola B14, Bacteroides succinogenes S85, Ruminococcus albus 7, Ruminococcus flavefaciens C94 and FD1, and Succinivibrio dextrinosolvens 22B. All xylans tested appeared to have a small fraction of carbohydrate that supported low levels of growth of nonxylanolytic strains such as Selenomonas ruminantium HD4. Compared to growth on hexoses, the same array of fermentation acids was produced upon growth on xylans for most strains; however, reduced lactate levels were observed for B. fibrisolvens 49 and Selenomonas ruminantium HD4. Measurements of enzyme activities of B. fibrisolvens AcTF2, 49, H17c, and D1 indicated that the xylobiase activities were cell associated and that the xylanase activities were predominantly associated with the culture fluid. The pattern of expression of these enzymes varied both between strains and between the carbon sources on which the strains were grown.     

Inhibitory Effects of Methylcellulose on Cellulose Degradation by Ruminococcus flavefaciens

Highly methylated, long-chain celluloses strongly inhibited cellulose degradation by several species of cellulolytic bacteria of ruminal origin. Specifically, the inhibitory effects of methylcellulose on the growth of Ruminococcus flavefaciens FD1 were concentration dependent, with complete inhibition at 0.1% (wt/vol). However, methylcellulose did not inhibit growth on cellobiose or cellulooligosaccharides. Mixtures of methylated cellulooligosaccharides having an average degree of polymerization of 6.7 to 9.5 inhibited cellulose degradation, but those with an average degree of polymerization of 1.0 to 4.5 did not. Similar inhibitory effects by methylcellulose and, to a lesser extent, by methyl cellulooligosaccharides were observed on cellulase activity, as measured by hydrolysis of p-nitrophenyl-beta-d-cellobioside. R. flavefaciens cultures hydrolyzed cellulooligosaccharides to cellobiose and cellotriose as final end products. Cellopentaose and cellohexaose were cleaved to these end products, but cellotetraose was also formed from cellohexaose. Methylcellulose did not inhibit hydrolysis of cellulooligosaccharides. These data are consistent with the presence of separate cellulase (beta-1,4-glucanase) and cellulodextrinase activities in R. flavefaciens.     

Some chemical and physical properties of extracellular polysaccharides produced by Butyrivibrio fibrisolvens strains

Most strains of Butyrivibrio fibrisolvens are known to produce extracellular polysaccharides (EPs). However, the rheological and functional properties of these EPs have not been determined. Initially, 26 strains of Butyrivibrio were screened for EP yield and apparent viscosities of cell-free supernatants. Yields ranged from less than 1.0 to 16.3 mg per 100 mg of glucose added to the culture. Viscosities ranged from 0.71 to 5.44 mPa.s. Five strains (CF2d, CF3, CF3a, CE51, and H10b) were chosen for further screening. The apparent viscosity of the EP from each of these strains decreased by only 50 to 60% when the shear rate was increased from 20 to 1,000 s-1. Strain CE51 produced the EP having the highest solution viscosity. A detailed comparison of shear dependency of the EP from strain CF3 with xanthan gum showed that this EP was less shear sensitive than xanthan gum and, at a shear rate of 1,000 s-1, more viscous. EPs from strains CF3 and H10b were soluble over a wide range of pH (1 to 13) in 80% (vol/vol) ethanol-water or in 1% (wt/vol) salt solutions. The pH of 1% EP solutions was between 4.5 and 5.5. Addition of acid increased solution viscosities, whereas addition of base decreased viscosity. EPs from strains CF3, CE51, and H10b displayed qualitatively similar infrared spectra. Calcium and sodium were the most abundant minerals in the three EPs. The amounts of magnesium, calcium, and iron varied considerably among the EPs, but the potassium contents remained relatively constant.     

Optimizing aerobic conversion of glycerol to 3-hydroxypropionaldehyde

When cells of Klebsiella pneumoniae NRRL B-199 (ATCC 8724) were grown aerobically on a rich glycerol medium and then suspended in buffer supplemented with semicarbazide and glycerol, aerobic conversion of glycerol to 3-hydroxypropionaldehyde (3-HPA) ensued. Depending on conditions, 0.38 to 0.67 g of 3-HPA were formed per gram of glycerol consumed. This means that up to 83.8% of the carbon invested as glycerol could potentially be recovered as the target product, 3-HPA. Production of 3-HPA was sensitive to the age of cells harvested for resuspension and was nonexistent if cells were cultivated on glucose instead of glycerol as the sole carbon source. Compared with 24- and 72-h cells, 48-h cells produced 3-HPA at the highest rate and with the greatest yield. The cell biomass concentration present during the fermentation was never particularly critical to the 3-HPA yield, but initial fermentation rates and 3-HPA accumulation displayed a linear dependence on biomass concentration that faded when biomass exceeded 3 g/liter. Fermentation performance was a function of temperature, and an optimum initial specific 3-HPA productivity occurred at 32 degrees C, although the overall 3-HPA yield increased continuously within the 25 to 37 degrees C range studied. The pH optimum based on fermentation rate was different from that based on overall yield; 8 versus 7, respectively. Initial glycerol concentrations in the 20 to 50 g/liter range optimized initial 3-HPA productivity and yield.     

Comparative evaluation of ethanol production by xylose-fermenting yeasts presented high xylose concentrations

Summary Three strains ofPichia stipitis and three ofCandida shehatae were compared withPachysolen tannophilus in their abilities to ferment xylose at concentrations as high as 200 g/L when subjected to both aerobic and microaerophilic conditions. Evaluations based on accumulated ethanol concentrations, ethanol productivities, xylose consumption, and ethanol and xylitol yields were determined from batch culture time courses. Of the strains considered,P.stipitis NRRL Y-7124 seemed most promising since it was able to utilize all but 7 g/L of 150 g/L xylose supplied aerobically to produce 52 g/L ethanol at a yield of 0.39 g per gram xylose (76% of theoretical yield) and at a rate comparable to the fastest shown byC.shehatae NRRL Y-12878. For all strains tested, fermentation results from aerobic cultures were more favorable than those from microaerophilic cultures.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Induction and glucose repression of xylanase from a color variant strain ofAureobasidum pullulans

Summary Xylose, xylobiose and arabinose were identified as natural and direct inducers of xylanase from a color variant strain ofAureobasidium pullulans. Arabinose, in contrast to xylose, xylobiose and xylan, induced only the major isozyme of xylanase. Xylanase induction was subject to glucose repression.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U. S. Department of Agriculture over other firms or similar products not mentioned.     

Physical and genetic characterization of linear DNA plasmids from the heterothallic yeastSaccharomycopsis crataegensis

Five strains of the heterothallic yeastSaccharomycopsis crataegensis have been previously shown to contain DNA and/or RNA plasmidlike molecules (Shepherd et al. 1987). Three DNA plasmids, designated pScrl-1,-2 and -3, were found in strain NRRL Y-5902, while two were identified in each of NRRL strains Y-5903 and Y-5904. DNA plasmids were not identified inS. crataegensis strains Y-5910 or YB-192. FourS. crataegensis strains (Y-5903, Y-5904, Y-5910 and YB-192) were also shown to possess double-stranded RNA (dsRNA) molecules not found in strain Y-5902 (Shepherd et al. 1987). Hybridization studies now demonstrate the DNA plasmids in Y-5903 and Y-5904 to be highly homologous to their respective size counterparts (pScrl-1 and pScrl-2) in Y-5902 and to show some homology to pScrl-3. Restriction endonuclease mapping studies confirm the linear nature of each plasmid and establish identical restriction maps for a 1.4 kilobase (kb) region in pScrl-2 and -3. This 1.4 kb region accounts for the hybridization homology of pScrl-2 and pScrl-3 noted by Shepherd et al. (1987) and for homology of the plasmids of Y-5903 and Y-5904 to pScrl-3 of Y-5902. The pScrl plasmids show no homology to the dsRNA molecules ofS. crataegensis, the 2 M circular DNA ofStaccharomyces cerevisiae, the killer plasmids ofKluyveromyces lactis, or the linear DNA plasmids ofPichia inositovora.In crosses between linear DNA plasmid-containing and dsRNA-containing strains, only progeny containing the pScrl plasmids were recovered. Poor spore viability and a lack of complete tetrad recovery limited the extent of the analysis, but the findings suggest a cytoplasmic mode of inheritance for these linear DNAs.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Glycerol accumulation while recycling thin stillage in corn fermentations to ethanol

Summary By succesive recycling of the thin stillage in mashing and fermenting fresh corn, the glycerol content in each fermentation increased by about 0.4% and accumulated to a high of 2.1% in the beer of the fifth recycle. Glycerol concentration declined after the fifth recycle. The original fermentation contained 0.8% glycerol.Presented in part at the Society for Industrial Microbiology Annual Meeting, August 7–12, 1988, Chicago, IL.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Glucose tolerant and thermophilic β-glucosidases from yeasts

Summary Forty-eight yeast strains belonging to the genera Candida, Debaryomyces, Kluyveromyces and Pichia (obtained from the ARS Culture Collection, Peoria, IL) were screened for production of extracellular glucose tolerant and thermophilic -glucosidase activity using p-nitrophenyl--D-glucoside as substrate. Enzymes from 15 yeast strains showed very high glucose tolerance (<50 % inhibition at 30 %, w/v glucose). The optimal temperatures and pH for these -glucosidase activities varied from 30 to 65°C and pH 4.5 to 6.5. The -glucosidases from all these yeast strains hydrolyzed cellobiose.Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.