@article {3131, title = {A Geobacter sulfurreducens strain expressing pseudomonas aeruginosa type IV pili localizes OmcS on pili but is deficient in Fe(III) oxide reduction and current production.}, journal = {Appl Environ Microbiol}, volume = {80}, year = {2014}, month = {2014 Feb}, pages = {1219-24}, abstract = {

The conductive pili of Geobacter species play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili of Geobacter sulfurreducens have a metal-like conductivity, independent of the presence of c-type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain of G. sulfurreducens, designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene of Pseudomonas aeruginosa PAO1. Strain PA expressed and properly assembled P. aeruginosa PilA subunits into pili and exhibited a profile of outer surface c-type cytochromes similar to that of a control strain expressing the G. sulfurreducens PilA. Surprisingly, the strain PA pili were decorated with the c-type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of the G. sulfurreducens PilA that are necessary for conductivity.

}, keywords = {Amino Acid Sequence, Cytochromes c, Electricity, Ferric Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Methanosarcinaceae, Molecular Sequence Data, Oxidation-Reduction, Pseudomonas aeruginosa, Sequence Alignment}, issn = {1098-5336}, doi = {10.1128/AEM.02938-13}, author = {Liu, Xing and Tremblay, Pier-Luc and Malvankar, Nikhil S and Nevin, Kelly P and Lovley, Derek R and Vargas, Madeline} } @article {3142, title = {Aromatic amino acids required for pili conductivity and long-range extracellular electron transport in Geobacter sulfurreducens.}, journal = {mBio}, volume = {4}, year = {2013}, month = {2013 Mar 12}, pages = {e00105-13}, abstract = {

UNLABELLED: It has been proposed that Geobacter sulfurreducens requires conductive pili for long-range electron transport to Fe(III) oxides and for high-density current production in microbial fuel cells. In order to investigate this further, we constructed a strain of G. sulfurreducens, designated Aro-5, which produced pili with diminished conductivity. This was accomplished by modifying the amino acid sequence of PilA, the structural pilin protein. An alanine was substituted for each of the five aromatic amino acids in the carboxyl terminus of PilA, the region in which G. sulfurreducens PilA differs most significantly from the PilAs of microorganisms incapable of long-range extracellular electron transport. Strain Aro-5 produced pili that were properly decorated with the multiheme c-type cytochrome OmcS, which is essential for Fe(III) oxide reduction. However, pili preparations of the Aro-5 strain had greatly diminished conductivity and Aro-5 cultures were severely limited in their capacity to reduce Fe(III) compared to the control strain. Current production of the Aro-5 strain, with a graphite anode serving as the electron acceptor, was less than 10\% of that of the control strain. The conductivity of the Aro-5 biofilms was 10-fold lower than the control strain{\textquoteright}s. These results demonstrate that the pili of G. sulfurreducens must be conductive in order for the cells to be effective in extracellular long-range electron transport.

IMPORTANCE: Extracellular electron transfer by Geobacter species plays an important role in the biogeochemistry of soils and sediments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geochemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacter organisms are often abundant in such environments. Geobacter sulfurreducens produces the highest current densities of any known pure culture, and close relatives are often the most abundant organisms colonizing anodes in microbial fuel cells that harvest electricity from wastewater or aquatic sediments. The finding that a strain of G. sulfurreducens that produces pili with low conductivity is limited in these extracellular electron transport functions provides further insight into these environmentally significant processes.

}, keywords = {Amino Acids, Aromatic, Bioelectric Energy Sources, Biofilms, Electricity, Electrodes, Electron Transport, Ferric Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Graphite}, issn = {2150-7511}, doi = {10.1128/mBio.00105-13}, author = {Vargas, Madeline and Malvankar, Nikhil S and Tremblay, Pier-Luc and Leang, Ching and Smith, Jessica A and Patel, Pranav and Snoeyenbos-West, Oona and Nevin, Kelly P and Lovley, Derek R} }