Simultaneos syngas fermentation and chain elongation by an adapted microbiome

In this study, we autotrophically adapted a dark fermentation microbiome by using H2 and inorganic carbon to enable simultaneous syngas fermentation and chain elongation, yielding up to 92.1 mM caproate. The adapted microbiome exhibited homoacetogenic and carboxydotrophic activity, converting syngas into acetate, butyrate, and caproate. Four pressure conditions (1.0, 1.2, 1.4, and 1.6 atm) were tested using syngas (40% CO, 30% CO2 , 30% H2 ) showing carboxylate selectivity torwards medium chain compounds. Moreover, the adapted microbiome was capable of fermenting CO (50% CO, 50% N2 ) as the only carbon and energy source. Microbial community analysis revealed that syngas fermentation samples were dominated by Haloimpatiens and Clostridium sensu stricto 12. In contrast, under CO fermentation Citrobacter became dominant. These findings suggest that both syngas and CO fermentation significantly influence communitystructure and metabolic outputs, despite originating from the same adapted microbiome.