Electrically conductive pili from pilin genes of phylogenetically diverse microorganisms

ISME J. 2018 Jan;12(1):48-58. doi: 10.1038/ismej.2017.141. Epub 2017 Sep 5.

Abstract

The possibility that bacteria other than Geobacter species might contain genes for electrically conductive pili (e-pili) was investigated by heterologously expressing pilin genes of interest in Geobacter sulfurreducens. Strains of G. sulfurreducens producing high current densities, which are only possible with e-pili, were obtained with pilin genes from Flexistipes sinusarabici, Calditerrivibrio nitroreducens and Desulfurivibrio alkaliphilus. The conductance of pili from these strains was comparable to native G. sulfurreducens e-pili. The e-pili derived from C. nitroreducens, and D. alkaliphilus pilin genes are the first examples of relatively long (>100 amino acids) pilin monomers assembling into e-pili. The pilin gene from Candidatus Desulfofervidus auxilii did not yield e-pili, suggesting that the hypothesis that this sulfate reducer wires itself with e-pili to methane-oxidizing archaea to enable anaerobic methane oxidation should be reevaluated. A high density of aromatic amino acids and a lack of substantial aromatic-free gaps along the length of long pilins may be important characteristics leading to e-pili. This study demonstrates a simple method to screen pilin genes from difficult-to-culture microorganisms for their potential to yield e-pili; reveals new sources for biologically based electronic materials; and suggests that a wide phylogenetic diversity of microorganisms may use e-pili for extracellular electron exchange.

MeSH terms

  • Deltaproteobacteria / chemistry*
  • Deltaproteobacteria / classification
  • Deltaproteobacteria / genetics*
  • Deltaproteobacteria / metabolism
  • Electric Conductivity
  • Fimbriae Proteins / genetics*
  • Fimbriae Proteins / metabolism
  • Fimbriae, Bacterial / chemistry*
  • Fimbriae, Bacterial / genetics
  • Fimbriae, Bacterial / metabolism
  • Methane / metabolism
  • Oxidation-Reduction
  • Phylogeny*

Substances

  • Fimbriae Proteins
  • Methane