Microbial electrolysis cells reactor sample Targeted Locus (Loci). bioreactor metagenome

Propionate is a key intermediate of anaerobic fermentation. Under methanogenic conditions, propionate oxidation needs syntrophy between propionate fermenting bacteria and H2-utilizing methanogens. Propionate is previously used as an electron donor in microbial fuel cells (MFCs). However preferable pathways for propionate oxidation in MECs and MFCs are unknown. Here we examined the pathways involved for propionate oxidation, reactor performance, electron balances and microbial communities in two-chambered MECs at low (500 mg COD/l) and high (4000 mg COD/l) concentrations. Propionate oxidation in MECs happened through syntrophy by production of intermediates (acetate, formate & H2).The current was the largest electron sink in low and high propionate loading. Low propionate loading (PL) showed the coulombic efficiency (CE) was 91%. However, high propionate loading (PH) can decrease the CE to 66%. We have discovered unexpected changes also occur with propionate as a result of syntrophy. By suppression of methanogensis using 2-bromoethanesulfonate (BES) at PL, increased the CE by 5% by establishing stable syntrophy between propionate fermenters and metabolite consumers (exoelectrogens and other batceria). On contrary, PH with BES decreased the CE by 9%. This signifies, at PH for better system performance, requires syntrophy among propionate fermenters, methanogens and metabolite consuming bacteria (exoelectrogens and other bacteria). G.sulfurreducens PCA was the dominant organisms at PL however PH communities were more diverse and dominated by G.sulfurreducens PCA, A. colombiense, and C. aciduri. The dominant methanogens is hydrogentrophic, Methanobacterium sp. in PL and PH. At both propionate loading have shown better removal efficiency (78 – 98%).