@article {3136, title = {Anaerobic benzene oxidation via phenol in Geobacter metallireducens.}, journal = {Appl Environ Microbiol}, volume = {79}, year = {2013}, month = {2013 Dec}, pages = {7800-6}, abstract = {

Anaerobic activation of benzene is expected to represent a novel biochemistry of environmental significance. Therefore, benzene metabolism was investigated in Geobacter metallireducens, the only genetically tractable organism known to anaerobically degrade benzene. Trace amounts (<0.5 μM) of phenol accumulated in cultures of Geobacter metallireducens anaerobically oxidizing benzene to carbon dioxide with the reduction of Fe(III). Phenol was not detected in cell-free controls or in Fe(II)- and benzene-containing cultures of Geobacter sulfurreducens, a Geobacter species that cannot metabolize benzene. The phenol produced in G. metallireducens cultures was labeled with (18)O during growth in H2(18)O, as expected for anaerobic conversion of benzene to phenol. Analysis of whole-genome gene expression patterns indicated that genes for phenol metabolism were upregulated during growth on benzene but that genes for benzoate or toluene metabolism were not, further suggesting that phenol was an intermediate in benzene metabolism. Deletion of the genes for PpsA or PpcB, subunits of two enzymes specifically required for the metabolism of phenol, removed the capacity for benzene metabolism. These results demonstrate that benzene hydroxylation to phenol is an alternative to carboxylation for anaerobic benzene activation and suggest that this may be an important metabolic route for benzene removal in petroleum-contaminated groundwaters, in which Geobacter species are considered to play an important role in anaerobic benzene degradation.

}, keywords = {Anaerobiosis, Benzene, Carbon Dioxide, Gene Deletion, Gene Expression Profiling, Geobacter, Iron, Metabolic Networks and Pathways, Oxidation-Reduction, Phenol, Water}, issn = {1098-5336}, doi = {10.1128/AEM.03134-13}, author = {Zhang, Tian and Tremblay, Pier-Luc and Chaurasia, Akhilesh Kumar and Smith, Jessica A and Bain, Timothy S and Lovley, Derek R} } @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} }