Microbial community ecology in bioelectrochemical systems (BESs) using 16S ribosomal RNA (rRNA) pyrosequencing

Abstract

Microbial community ecology in bioelectrochemical systems (BES) has provided useful information on the fundamental understanding of microbial community structure and function for bioenergy production. With rapidly developing high-throughput DNA sequencing technologies coupled with bioinformatics tools, the deep sequencing has become a popular tool to provide better understanding complex interactions occurring in bioenergy-producing microbial communities in BES.

In this thesis, I analyzed the microbial community from variable characteristics of BESs including microbial fuel cell (MFC) media solutions enriched by Rhodopseudomonas sp, methanogenic biocathodes inoculated with different inoculum sources, newly designed MFCs under nitrogen-rich conditions and alkaline MFCs, using 16S rRNA gene pyrosequencing.

My results indicated: 1) a syntrophic relationship between Rhodopseudomonas and hydrogenotrophic microbes could exist in the acetate-fed MFCs under light conditions. Observations suggested that high power densities obtained from the light-induced MFC reactors might be explained by not only the enrichment of Rhodopseudomonas palustris but also its respective syntrophic assosociates; 2) Major groups of unknown bacteria in the phyla Firmicutes and Bacteroidetes originated from the biocathodes with different inoculum sources including the sludge (BIS) and effluent of acetate-fed microbial fuel cell (BIE), suggesting them to be involved in hydrolysis, acidogenesis and acetogenesis. They could play an important role in CO2 production for methane generation by three major hydrogenotrophic methanogens identified as Methanobacterium, Methanocorpusculum and Methanobacterium. Their specific roles in the reduction of CO2 to methane may be due to external power and/or H2 used as electron donors; 3) the additional electrode-like biocathode in the newly designed nitrogen-rich MFCs showed inhibition of true nitrifiers as the potential exoelectrogen in the anode biofilm. The dominance of Geobacter in the additional electrode-like biocathode could be mainly involved in denitrification processes; 4) The Desulfuromonas species was the most prevalent bacterial species in pH10 and 11 MFC reactors with its abundance trend consistent with higher levels of power density. It was suggested that the possibility of their activities might be related to the amount of electricity generated. The dominant Desulfuromonas of pH10 and 11 MFC reactors could outcompete other exoelectrogens for acetate and this resulted in lower bacterial diversity and linking their abundance values with higher power generation.

Overall, these distinct microbial community compositions provided useful information for a better understanding of microbial interactions and functions associated with the different operating conditions of electricity and methane generation in BESs.