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

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°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. © 1994 John Wiley & Sons, Inc.