Development of a synthetic medium for continuous anaerobic growth and ethanol production with a lactate dehydrogenase mutant of Bacillus stearothermophilus

Abstract

A synthetic medium was developed by the pulse and medium-shift technique for the continuous cultivation ofBucUus sfeurothermophh strain LLD-15 (NCIMB 12428) under anaerobic conditions. This mutant strah lacks L-lactate dehydrogenase activity, and is a promising candidate for the production of ethanol from pentoses and hex-, using a high-temperature two-stage process. The final medium contained four amino acids and five Vitamins, and growth characterhtics in this medium compared well with those in complex medium Containing yeast extract and tryptone. At 70 "C, the medium was capable of supporting good anaerobic and aerobic growth at 10 g input sucrose 1-I. High ethanol production indicated that pyruvate metabolism probably occurred via the combined activity of the pyruvate-formate-lyase pathway and pyruvate dehydrogenase.

Emulsion formation and stability during reversed micelle extraction

“…KCl, NaCl, K 2 HPO 4 and KH 2 PO 4 were of analytical grade and purchased from Rose Chemicals, UK. Bacillus stearothermophilus fermentation broth in complex medium, without antibiotics, and with antifoaming agent Dow Corning 1510 EU (BDH, UK) was kindly provided by Dr David Leak, Department of Biochemistry, Imperial College, London, UK 10. The broth was centrifuged and filtered (0.22 µm) to remove microorganisms and debris before use in the experiments reported here.…”

Extremophiles and their Application to Biofuel Research

“…Early strain development sought the isolation of lactate dehydrogenase (ldh)-deficient variants through classical mutagenesis and selection methods (San Martin et al, 1992Martin et al, ,1994. Such an approach proved unstable, in that cultures were reported to revert back to the original phenotype after multiple generations in the absence of the mutagen, fluoropyruvate (San Martin et al, 1994).…”

“…Such an approach proved unstable, in that cultures were reported to revert back to the original phenotype after multiple generations in the absence of the mutagen, fluoropyruvate (San Martin et al, 1994). Stable deletion mutants were, however, developed via targeted molecular disruption of the ldh gene (San Martin et al, 1992.…”

Extremophiles in biofuel synthesis

“…Certain species are able to ferment sugars such as D-glucose, D-xylose and L-arabinose at temperatures between 55 ° C and 70 ° C and to produce a mixture of lactate, formate, acetate and ethanol from glucose [98]. More complex carbohydrates such as xylan are also degraded by certain Geobacillus strains owing to the presence of xylanases [99].…”