P56: The role of secondary metabolism in extracellular electron transfer by a microaerophilic marine Streptomyces strain

The largely marine MAR4 lineage of streptomycetes has been linked to the production of a rare class of secondary metabolites known as hybrid isoprenoids. While the ecological functions of bacterially produced hybrid isoprenoids remain unknown, the compounds produced by MAR4 strains include redox active molecules such as prenylated phenazines and quinones, which resemble molecules that function in electron transport.  Although some Gram-positive bacteria are known to use electron shuttles as alternate electron acceptors, none have been shown to produce these compounds endogenously.  Here we show that phenazine production in a MAR4 strain is up regulated in microaerophilic conditions.  This led to the hypothesis that prenylated phenazines function as endogenous extracellular electron shuttles in this strain.  In support of this hypothesis, a MAR4 strain was observed to reduce an electrode in the absence direct cellular contact.  To our knowledge, this is the first time a member of the Phylum Actinobacteria has been shown to produce a current via extracellular electron transfer.  Furthermore, this is the first demonstration of current production in an obligate aerobe, suggesting that extracellular electron transfer may be associated with a broader range of bacteria than previously acknowledged.  This study expands upon the ecological functions of actinobacterial secondary metabolites and identifies a new group of organisms that can be studied in the context of microbial fuel cell development.