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: H₂ production from cellulose by six mesophilic clostridia was characterized in standardized batch experiments using MN301 cellulose, Avicel and cellobiose. Daily H₂ 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 H₂ from cellobiose, with Clostridium acetobutylicum achieving the highest H₂ 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 ₂mol^-1 hexose from MN301 and 1.6 and 1.4 mol H₂ mol^-1 hexose from Avicel, respectively. These species also achieved 25-100% higher H₂ production rates from cellulose than the other species. Conclusions: These cellulolytic, hydrogen-producing clostridia varied in H₂ production, with Cl. cellulolyticum and Cl. populeti achieving the highest H₂ yields and cellulose degradation. Significance and Impact of the Study: The fermentation of cellulosic materials presents a means of H₂ production from renewable resources. This standardized comparison provides a quantitative baseline for improving H₂ production from cellulose through medium and process optimization and metabolic engineering.