Transcriptomic responses of the interactions between Clostridium cellulovorans 743B and Rhodopseudomonas palustris CGA009 in a cellulose-grown coculture for enhanced hydrogen production

Coculturing dark- and photofermentative bacteria is a promising strategy for enhanced hydrogen (H₂) production. In this study, next-generation sequencing was used to query the global transcriptomic responses of an artificial coculture of Clostridium cellulovorans 743B and Rhodopseudomonas palustris CGA009. By analyzing differentially regulated gene expression, we showed that, consistent with the physiological observations of enhanced H₂ production and cellulose degradation, the nitrogen fixation genes in R. palustris and the cellulosomal genes in C. cellulovorans were upregulated in cocultures. Unexpectedly, genes related to H₂ production in C. cellulovorans were downregulated, suggesting that the enhanced H₂ yield was contributed mainly by R. palustris. A number of genes related to biosynthesis of volatile fatty acids (VFAs) in C. cellulovorans were upregulated, and correspondingly, a gene that mediates organic compound catabolism in R. palustris was also upregulated. Interestingly, a number of genes responsible for chemotaxis in R. palustris were upregulated, which might be elicited by the VFA concentration gradient created by C. cellulovorans. In addition, genes responsible for sulfur and thiamine metabolism in C. cellulovorans were downregulated in cocultures, and this could be due to a response to pH changes. A conceptual model illustrating the interactions between the two organisms was constructed based on the transcriptomic results. Copyright © 2016, American Society for Microbiology. All Rights Reserved.