Production of acetate by mutant strains of Clostridium thermoaceticum

Summary Mutant strains were derived from Clostridium thermoaceticum ATCC 39 289 by treatment with chemical mutagenic agents and selective enrichment procedures. Some mutant strains exhibited growth when cultured in media containing 20 mabetm (1.75 g l^–1) pyruvate of high-magnesium lime (dolime) above pH 6.0. One strain (G-20) grew and produced acetate when 80 mabetm (7 gl^–1) pyruvate or 50 mabetm (2.3 g l^–1) formate at pH 5.6 was the sole energy source. In a fed-batch process controlled at pH 6.2, this mutant produced 52.5 g l^–1 acetate (equivalent to 72.5 g l^–1 Na acetate) and 67 g l^–1 calcium-magnesium acetate (CMA) in 140 h when dolime was the neutralizing agent, with 93% substrate utilization. This mutant strain holds promise for CMA production due to its better tolerance of dolime and its ability to synthesize high levels of acetic acid. Offprint requests to: S. R. Parekh     

Production of glycerol by hansenula anomala

Production of glycerol by Hansenula anomala in molasses-corn steep liquor based media was studied. The accumulation and yield of glycerol was dependent on the medium composition and aeration rate; pH control did not affect the yield. Intermittent addition of sugar during fermentation resulted in significant increase in production of glycerol.     

SO2-catalysed prehydrolysis of coniferous wood for ethanol production

Summary This paper reports studies of large scale, 1500 kg/h, SO₂-catalysed prehydrolysis of coniferous wood chips, samples then being hydrolyzed by a wood-saccharifying enzyme system followed by fermentation to ethanol in the laboratory. Hemicellulose hydrolysis using SO₂ catalyst (prehydrolysis) was found to be more effective than steam alone (autohydrolysis). Prehydrolysis time was 2 min, with steam pressure at 1.2 to 1.7 MPa (175 to 250 psig), and SO₂ catalyst 2.0 to 2.6% on dry wood. The amount of sugars recovered upon enzyme saccharification of the prehydrolysed wood was about 70% of the weight of the wood. When these combined hemicellulose and cellulose sugars were fermented by a pentose-fermenting strain of yeast,Pichia stipitis R, 372 L ethanol/tonne of (dry) wood was obtained.     

Determination of Gardnerella vaginalis Genome Size by Pulsed-Field Gel Electrophoresis

The chromosomal DNA of four strains of Gardnerella vaginaliswere digested with rare cutting restriction enzymes and analyzedby pulsed-field gel electrophoresis (PFGE). The four strainsstudied were two clinical isolates (GVP 004 & GVP 007) andtwo American Type Culture Collection strains (ATCC 14018 &ATCC 14019). The restriction enzyme SfiI generated two DNA fragmentsof about 0.6 Mb and 1.1 Mb in all four strains giving a G. vaginalisgenome size of about 1.7 Mb. A similar genome size was calculatedutilizing two more GC-rich sequence specific restriction endonucleases,NotI and AscI. When digested with AscI, the chromosomal DNAof all four strains gave rise to 11 to 12 DNA fragments rangingbetween 0.01 Mb to 0.43 Mb. DNA from the two clinical isolateswere digested by NotI (yielding 7 to 9 fragments), while theDNA from the two ATCC strains were resistant to NotI digestion.In contrast to the clinical isolates, DNA from the two ATCCstrains gave an identical profile for all restriction endonucleasestested. From double digestion experiments, the two SfiI sitescould be localized on two AscI fragments. From these PFGE studies,it is concluded that the G. vaginalis genome is a circular DNAthat ranges between 1.67 Mb and 1.72 Mb in size.     

Post-translational modification of proteins and the discovery of new medicine

Post-translational modifications are fundamental to processes controlling behaviour, including cellular signaling, growth and transformation. As the molecular basis of protein modifications in normal and disease processes are becoming better defined, so new strategies for designing therapeutic entities to control complex disease processes are emerging.     

On the interaction of tritiated 2-ketobutyrate with 2-keto-3-deoxygluconate-6P aldolase ofPseudomonas putida. Evidence suggesting enzyme-mediated,uncatalyzed tritium exchange

2-Keto-3-deoxygluconate-6P aldolase ofPseudomonas putida mediates exchange between hydrogen isotope at the methylene carbon of 2-ketobutyrate and water. This occurs with aK _m of 20 mM, 100 times the corresponding value for pyruvate, and a V_max approximating 1/710 that of KDPG cleavage. Ketobutyrate is competitive with both pyruvate and 2-keto-3-deoxygluconate-6P for the enzyme. In addition, there is no evidence for C-C synthesis between ketobutyrate andd-glyceraldehyde-3P. A comparison of relativeV/K values for hydrogen exchange shows pyruvate to be 17,600 times better as a substrate than ketobutyrate. The detritiation of [3-³H]ketobutyrate is stereochemically random. In addition, the reaction proceeds with ak _H/k _T isotope effect of 15.3, consistent with C-H bond turnover being rate-determining. The E-ketobutyrate complex is reductively trapped, inactivating the enzyme. Reductive inactivation kinetics of E-ketobutyrate compared to E-pyruvate suggests more of the complex may be partitioned to ketimine in the ketobutyrate case than in the pyruvate case. A mechanism is considered in which ketobutyrate is bound as a ketimine in an orientation such that the active site acid/basic group cannot mediate catalytic ketimine/eneamine interconversion. Thus, exchange would result from hydrogen ionization at C-3′ of the ketimine, a slow spontaneous step compared to overall complex turnover. This noncatalyzed deprotonation would explain dissymmetry in exchange, the poorV/K compared to pyruvate, and a large tritium isotope effect.     

Reactivity of cuprous stellacyanin as a quinone and semiquinone reductase

The reactivity of cuprous stellacyanin as a quinone and semiquinone reductase has been examined. Rate constants (25.0 degrees C) measured for the oxidation of stellacyanin by 1,4-benzoquinone and benzosemiquinone are 2.3 X 10(4) M-1 s-1 (delta H not equal to = 4.4 kcal/mol, delta S not equal to = -24 eu) and 5.1 X 10(6) M-1 s-1, respectively [pH 7.0, I = 0.1 M (phosphate)]. The agreement of these rate constants with those calculated on the basis of relative Marcus theory is discussed. Stellacyanin is more effective than laccase in quenching benzosemiquinone, suggesting that the physiological role of this metalloprotein is to regulate the concentration of free radicals generated through the laccase-catalyzed oxidation of phenols.     

Net above-ground biomass and production in the monsoonal vegetation at Jodhpur,Rajasthan, India

The observations on net above-ground biomass and production in a large protected area of monsoonal vegetation at Jodhpur (India) are presented in this paper. With the start of the monsoon (July–August) a distinct increase in biomass was noted and by winter (November–December), the biomass, decreased as there was hardly any moisture in the soil. The ephemerals, especially some of the grasses form the bulk of biomass in the total make-up. The biomass and production appeared to be closely related in the monsoonal vegetation of this area. The maximum biomass value (360.5 g/m²) was observed in the month of September, decreasing thereafter.