S148: Extracellular electron transport: changes in biofilm activity in response to surface potential

In recent years, it has become clear that microbial respiration via extracellular electron transfer (EET) is a common part of environmental microbial metabolism. EET allows microbes to exchange electrons with solid substrates, be they insoluble metal oxides, corrosion sensitive metal materials, or electrodes. Here we describe the ability of a mixed biofilm community growing on the anode of a microbial fuel cell to respond to a change in surface potential of the electrode.  When the potential of the anode was increased by 100 mV, there was a community-wide response that was manifested by an increase in electron flow.  However, when the transcriptome of the biofilm community was analyzed, it was seen that only two microbial groups (Desulfobulbaceae and Desulfuromonadales) had significantly responded to the change in surface potential.  Metagenomic analyses yielded high coverage draft genomes of these abundant and active microbes, and metatranscriptomics revealed known and unknown genes that were highly responsive to the change in surface potential.  When the increased potential was removed by EET stimuli the same genes were down-regulated.  These results indicate that microbes are capable of sensing, and rapidly responding to surface charge, and that the response can be a major change in the rate of EET.