Comparative proteomics implicates a role for multiple secretion systems in electrode-respiring Geobacter sulfurreducens biofilms

Geobacter sulfurreducens is a dissimilatory metal-reducing bacterium capable of forming thick electron-conducting biofilms on solid electrodes. Here, we employ for the first time comparative proteomics to identify key physiological changes involved in G. sulfurreducens adaptation from fumarate-respiring planktonic cells to electron-conducting biofilms. Increased levels of proteins involved in outer membrane biogenesis, cell motility and secretion are expressed in biofilms. Of particular importance to the electron-conducting biofilms are proteins associated with secretion systems of Type I, II, V and Type IV pili. Furthermore, enzymes involved in lipopolysaccharide and peptidoglycan biosynthesis show increased levels of expression in electron-conducting biofilms compared to planktonic cells. These observations point to similarities in long-range electron transfer mechanisms between G. sulfurreducens and Shewanella oneidensis, while highlighting the wider significance of secretion systems beyond that of Type IV pili identified to date in the adaptation of G. sulfurreducens to electrode respiration.