Cultivation of an L‐lactate dehydrogenase mutant of Bacillus stearothermophilus in continuous culture with cell recycle

Abstract

Continuous fermentation with cell recycle proved very effective in increasing the ethanol volumetric productivity of the thermophilic facultative anaerobe, Bacillus stearothermophilus strain LLD-15, on sucrose at 70 degrees C. When complete cell recycle was used, cell viability decreased after a few residence times and sucrose consumption was reduced. Operation using a constant bleed rate resulted in greater stability and higher ethanol volumetric productivities. A mathematical model based on maintenance energy requirements provided an adequate description of the system.

Near‐zero growth kinetics of Pseudomonas putida deduced from proteomic analysis

“…Experimental studies on the maintenance state using the CCR or other continuous cultivation techniques are limited and contradictory. CCR was applied to diverse microorganisms (Chesbro et al, 1979;Arbige and Chesbro, 1982;Dorofeev et al, 1984;Panikov et al, 1985;Verseveld et al, 1986;Major and Bull, 1989;Uribelarrea et al, 1990;Evdokimova et al, 1994;Martin et al, 1994;Tappe et al, 1996;Tros et al, 1996;Palmqvist et al, 1998;Boender et al, 2009;Jørgensen et al, 2010), and some results seemed to comply with the simple chemostat model (Major and Bull, 1989;Uribelarrea et al, 1990;Martin et al, 1994;Tros et al, 1996;Palmqvist et al, 1998;Tappe et al, 1999), although the duration of experiments was never sufficiently long to demonstrate the attainment of a true and stable maintenance state. Other experiments, however, revealed considerable deviations, attributed mainly to the changes in the physiological state of microbial culture during prolonged continuous cultivation.…”

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). Stable deletion mutants were, however, developed via targeted molecular disruption of the ldh gene (San Martin et al, 1992.…”

Why and How Membrane Bioreactors with Unsteady Filtration Conditions Can Improve the Efficiency of Biological Processes

“…Thus, volumetric productivities are not enhanced as expected. Above a critical cell concentration, the growth rate is apparently zero 26. Nutritive limitations could partly explain this result, but in most cases an increase in dilution rate that could solve this problem cannot be realized because of membrane fouling 12.…”

“…Above a critical cell concentration, the growth rate is apparently zero. 26 Nutritive limitations could partly explain this result, but in most cases an increase in dilution rate that could solve this problem cannot be realized because of membrane fouling. 12 To justify the decrease in the microbial specific activity, studies have also pointed out the possible retention by the filter of toxic compounds, 27 but in most cases a suitable choice of the membrane can avoid this problem.…”