Characterization of the cellulolytic and hydrogen-producing activities of six mesophilic Clostridium species.

Aims: To characterize cellulolytic, hydrogen-producing clostridia on a comparable basis.
Methods and Results: H(2) production from cellulose by six mesophilic clostridia was characterized in standardized batch experiments using MN301 cellulose, Avicel and cellobiose. Daily H(2) production, substrate degradation, biomass production and the end-point distribution of soluble fermentation products varied with species and substrates. All species produced a significant amount of H(2) from cellobiose, with Clostridium acetobutylicum achieving the highest H(2) yield of 2.3 mol H(2) mol(-1) hexose, but it did not degrade cellulose. Clostridium cellulolyticum and Clostridium populeti catalysed the highest H(2) production from cellulose, with yields of 1.7 and 1.6 mol H(2 )mol(-1) hexose from MN301 and 1.6 and 1.4 mol H(2) mol(-1) hexose from Avicel, respectively. These species also achieved 25-100% higher H(2) production rates from cellulose than the other species.
Conclusions: These cellulolytic, hydrogen-producing clostridia varied in H(2) production, with Cl. cellulolyticum and Cl. populeti achieving the highest H(2) yields and cellulose degradation.
Significance and Impact of the Study: The fermentation of cellulosic materials presents a means of H(2) production from renewable resources. This standardized comparison provides a quantitative baseline for improving H(2) production from cellulose through medium and process optimization and metabolic engineering.