Enhanced hydrogen production from lignocellulosic substrates via bioaugmentation with Clostridium strains

Abstract

Bioaugmentation could be a useful strategy to convert directly lignocellulosic substrates to hydrogen via fermentation. In co-culture tests, different inoculation ratios of a hydrolytic member (Clostridium cellulovorans, Cc) to a fermentative member (Clostridium acetobutylicum, Ca) were tested for hydrogen production from wheat straw. Under sterile conditions, both strains established a synergistic relationship where the inoculation ratio 5:3 (Cc:Ca) resulted in the highest hydrogen production of 128 mL/L, a 2- to 3-fold improvement in comparison with single cultures. However, the synergistic relationship between Cc and Ca was lost in the bioaugmentation of a native wheat straw microbial community, and the single cultures reached the highest hydrogen potential of 115 mL/L. When four native microbial communities of wheat straw, corn stover, agave bagasse and sugarcane bagasse were bioaugmented with Cc, improved hydrogen production was observed only in the treatments of grass biomasses, but not of bagasses. In summary, positive interactions between the hydrolytic and fermentative members were only observed in co-culture tests when the substrate was sterilized. In the presence of a host microbial community, bioaugmentation of bacteria must be in a proper concentration that allows them to prosper in the host habitat.