AUTHOR=Shi Liang , Fredrickson James K. , Zachara John M. 

TITLE=Genomic analyses of bacterial porin-cytochrome gene clusters

JOURNAL=Frontiers in Microbiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2014.00657

DOI=10.3389/fmicb.2014.00657

ISSN=1664-302X

ABSTRACT=<p>The porin-cytochrome (Pcc) protein complex is responsible for trans-outer membrane electron transfer during extracellular reduction of Fe(III) by the dissimilatory metal-reducing bacterium <italic>Geobacter sulfurreducens</italic> PCA. The identified and characterized Pcc complex of <italic>G. sulfurreducens</italic> PCA consists of a porin-like outer-membrane protein, a periplasmic 8-heme <italic>c</italic>-type cytochrome (<italic>c</italic>-Cyt) and an outer-membrane 12-heme <italic>c</italic>-Cyt, and the genes encoding the Pcc proteins are clustered in the same regions of genome (i.e., the <italic>pcc</italic> gene clusters) of <italic>G. sulfurreducens</italic> PCA. A survey of additionally microbial genomes has identified the <italic>pcc</italic> gene clusters in all sequenced <italic>Geobacter</italic> spp. and other bacteria from six different phyla, including <italic>Anaeromyxobacter dehalogenans</italic> 2CP-1, <italic>A. dehalogenans</italic> 2CP-C, <italic>Anaeromyxobacter</italic> sp. K, <italic>Candidatus</italic> Kuenenia stuttgartiensis, <italic>Denitrovibrio acetiphilus</italic> DSM 12809, <italic>Desulfurispirillum indicum</italic> S5, <italic>Desulfurivibrio alkaliphilus</italic> AHT2, <italic>Desulfurobacterium thermolithotrophum</italic> DSM 11699, <italic>Desulfuromonas acetoxidans</italic> DSM 684, <italic>Ignavibacterium album</italic> JCM 16511, and <italic>Thermovibrio ammonificans</italic> HB-1. The numbers of genes in the <italic>pcc</italic> gene clusters vary, ranging from two to nine. Similar to the metal-reducing (Mtr) gene clusters of other Fe(III)-reducing bacteria, such as <italic>Shewanella</italic> spp., additional genes that encode putative <italic>c</italic>-Cyts with predicted cellular localizations at the cytoplasmic membrane, periplasm and outer membrane often associate with the <italic>pcc</italic> gene clusters. This suggests that the Pcc-associated <italic>c</italic>-Cyts may be part of the pathways for extracellular electron transfer reactions. The presence of <italic>pcc</italic> gene clusters in the microorganisms that do not reduce solid-phase Fe(III) and Mn(IV) oxides, such as <italic>D. alkaliphilus</italic> AHT2 and <italic>I. album</italic> JCM 16511, also suggests that some of the <italic>pcc</italic> gene clusters may be involved in extracellular electron transfer reactions with the substrates other than Fe(III) and Mn(IV) oxides.</p>