Quantitative and qualitative differences were analyzed between planktonic and anode-biofilm bacterial communities developed in a cassette-electrode microbial fuel cell treating starch, peptone, and fish extract. Quantitative analyses based on protein contents and rRNA-gene copy numbers indicated that planktonic microbes were over eight-times more abundant than anode-biofilm microbes. Clone-library analyses of PCR-amplified 16S rRNA gene fragments revealed the presence of bacteria affiliated with the phyla Bacteroidetes, Firmicutes, and Proteobacteria in these two communities. The most abundant sequence was affiliated with the family Porphyromonadaceae, and accounted for over 50% and 20% of all the sequences in the planktonic- and biofilm-microbe libraries, respectively.
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