@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} } @article {446, title = {Alignment of the c-type cytochrome OmcS along pili of Geobacter sulfurreducens.}, journal = {Appl Environ Microbiol}, volume = {76}, year = {2010}, month = {2010 Jun}, pages = {4080-4}, abstract = {Immunogold localization revealed that OmcS, a cytochrome that is required for Fe(III) oxide reduction by Geobacter sulfurreducens, was localized along the pili. The apparent spacing between OmcS molecules suggests that OmcS facilitates electron transfer from pili to Fe(III) oxides rather than promoting electron conduction along the length of the pili.}, keywords = {Cytochromes c, Ferric Compounds, Fimbriae, Bacterial, Geobacter, Immunohistochemistry, Microscopy, Immunoelectron}, issn = {1098-5336}, doi = {10.1128/AEM.00023-10}, author = {Leang, Ching and Qian, Xinlei and Mester, T{\"u}nde and Lovley, Derek R} } @article {531, title = {Adaptation to disruption of the electron transfer pathway for Fe(III) reduction in Geobacter sulfurreducens.}, journal = {J Bacteriol}, volume = {187}, year = {2005}, month = {2005 Sep}, pages = {5918-26}, abstract = {Previous studies demonstrated that an outer membrane c-type cytochrome, OmcB, was involved in Fe(III) reduction in Geobacter sulfurreducens. An OmcB-deficient mutant was greatly impaired in its ability to reduce both soluble and insoluble Fe(III). Reintroducing omcB restored the capacity for Fe(III) reduction at a level proportional to the level of OmcB production. Here, we report that the OmcB-deficient mutant gradually adapted to grow on soluble Fe(III) but not insoluble Fe(III). The adapted OmcB-deficient mutant reduced soluble Fe(III) at a rate comparable to that of the wild type, but the cell yield of the mutant was only ca. 60\% of that of the wild type under steady-state culturing conditions. Analysis of proteins and transcript levels demonstrated that expression of several membrane-associated cytochromes was higher in the adapted mutant than in the wild type. Further comparison of transcript levels during steady-state growth on Fe(III) citrate with a whole-genome DNA microarray revealed a significant shift in gene expression in an apparent attempt to adapt metabolism to the impaired electron transport to Fe(III). These results demonstrate that, although there are many other membrane-bound c-type cytochromes in G. sulfurreducens, increased expression of these cytochromes cannot completely compensate for the loss of OmcB. The concept that outer membrane cytochromes are promiscuous reductases that are interchangeable in function appears to be incorrect. Furthermore, the results indicate that there may be different mechanisms for electron transfer to soluble Fe(III) and insoluble Fe(III) oxides in G. sulfurreducens, which emphasizes the importance of studying electron transport to the environmentally relevant Fe(III) oxides.}, keywords = {Adaptation, Physiological, Bacterial Outer Membrane Proteins, Base Sequence, Cytochromes c, DNA Primers, Electron Transport, Ferric Compounds, Gene Expression Regulation, Bacterial, Geobacter, Kinetics, Oxidation-Reduction, Reverse Transcriptase Polymerase Chain Reaction}, issn = {0021-9193}, doi = {10.1128/JB.187.17.5918-5926.2005}, author = {Leang, Ching and Adams, L A and Chin, K-J and Nevin, K P and Meth{\'e}, B A and Webster, J and Sharma, M L and Lovley, D R} }