Facultative Anaerobe Caldibacillus debilis GB1: Characterization and Use in a Designed Aerotolerant, Cellulose-Degrading Coculture with Clostridium thermocellum

Abstract

ABSTRACTDevelopment of a designed coculture that can achieve aerotolerant ethanogenic biofuel production from cellulose can reduce the costs of maintaining anaerobic conditions during industrial consolidated bioprocessing (CBP). To this end, a strain ofCaldibacillus debilisisolated from an air-tolerant cellulolytic consortium which included aClostridium thermocellumstrain was characterized and compared with theC. debilistype strain. Characterization of isolateC. debilisGB1 and comparisons with the type strain ofC. debilisrevealed significant physiological differences, including (i) the absence of anaerobic metabolism in the type strain and (ii) different end product synthesis profiles under the experimental conditions used. The designed cocultures displayed unique responses to oxidative conditions, including an increase in lactate production. We show here that when the two species were cultured together, the noncellulolytic facultative anaerobeC. debilisGB1 provided respiratory protection forC. thermocellum, allowing the synergistic utilization of cellulose even under an aerobic atmosphere.