Comparative transcriptomics of closely related Geobacter sulfurreducens strains uncovers strain-level variations in...

Members of Geobacter sulfurreducens are electroactive bacteria that transfer electrons to extracellular solid electron acceptors using extracellular electron transport (EET) pathways, thereby generating currents in bioelectrochemical systems (BESs). Studies have shown that different G. sulfurreducens strains generate different levels of current in BESs, while information is scarce as to molecular mechanisms behind strain-level variations in current generation. In order to gain insights into the strain-level variations, the present work comparatively analyzed G. sulfurreducens strains OSK2A and 60473 that are identified to be closely related in phylogenomic analyses. It is shown that 60473 generates larger current than OSK2A and forms thicker biofilms on electrodes. Comparative genomic analyses indicate that genes for catabolic and EET pathways in these strains are highly homologous (mostly over 99% identical in amino acid sequences). In contrast, comparative transcriptomics shows that expression levels of genes coding for extracellular proteins, including conductive pili and cytochrome nanowires, in the EET pathways are largely different between these strains, even though those for catabolic enzymes are relatively similar. These genes are expressed at substantially higher levels in strain 60473 than those in strain OSK2A. These results suggest that different levels of current generated by closely related G. sulfurreducens strains are attributable to differences in the expression of genes for extracellular proteins in the EET pathway.