Fully reversible current driven by a dual marine photosynthetic microbial community

•Fully reversible currents were observed only with a dual microbial community.•Cathodic oxygen reduction occurs at high working electrode potential.•Cathodic current is likely associated with γ-proteobacterium Congregibacter.•Anodic current reflects biofilm capability to indirectly convert light to electricity.•The highest solar bioanode (>100 mA m−2)/oxygen biocathode currents (>1000 mA m−2).

The electrochemical activity of two seawater microbial consortia were investigated in three-electrode bioelectrochemical cells. Two seawater inocula – from the Sunshine Coast (SC) and Gold Coast (GC) shores of Australia – were enriched at +0.6 V vs. SHE using 12/12 h day/night cycles. After re-inoculation, the SC consortium developed a fully-reversible cathodic/anodic current, with a max. of −62 mA m−2 during the day and +110 mA m−2 at night, while the GC exhibited negligible daytime output but +98 mA m−2 at night. Community analysis revealed that both enrichments were dominated by cyanobacteria, indicating their potential as biocatalysts for indirect light conversion to electricity. Moreover, the presence of γ-proteobacterium Congregibacter in SC biofilm was likely related to the cathodic reductive current, indicating its effectiveness at catalysing cathodic oxygen reduction at a surprisingly high potential. For the first time a correlation between a dual microbial community and fully reversible current is reported.

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