Dissimilatory iron reduction in Escherichia coli: identification of CymA of Shewanella oneidensis and NapC of E. coli as ferric reductases.

TitleDissimilatory iron reduction in Escherichia coli: identification of CymA of Shewanella oneidensis and NapC of E. coli as ferric reductases.
Publication TypeJournal Article
Year of Publication2008
AuthorsGescher, JS, Cordova CD, Spormann AM
JournalMolecular microbiology
Volume68
Issue3
Pagination706-19
Date Published2008 May
ISSN1365-2958
KeywordsBacterial Proteins, Cell Membrane, Cytochrome c Group, Escherichia coli, Escherichia coli Proteins, Ferric Compounds, FMN Reductase, Gene Expression Regulation, Bacterial, Genetic Complementation Test, Nitrate Reductases, Oxidation-Reduction, Shewanella, Spectrum Analysis
AbstractOver geological time scales, microbial reduction of chelated Fe(III) or Fe(III) minerals has profoundly affected today's composition of our bio- and geosphere. However, the electron transfer reactions that are specific and defining for dissimilatory iron(III)-reducing (DIR) bacteria are not well understood. Using a synthetic biology approach involving the reconstruction of the putative electron transport chain of the DIR bacterium Shewanella oneidensis MR-1 in Escherichia coli, we showed that expression of cymA was necessary and sufficient to convert E. coli into a DIR bacterium. In intact cells, the Fe(III)-reducing activity was limited to Fe(III) NTA as electron acceptor. In vitro biochemical analysis indicated that CymA, which is a cytoplasmic membrane-associated tetrahaem c-type cytochrome, carries reductase activity towards Fe(III) NTA, Fe(III) citrate, as well as to AQDS, a humic acid analogue. The in vitro specific activities of Fe(III) citrate reductase and AQDS reductase of E. coli spheroplasts were 10x and 30x higher, respectively, relative to the specific rates observed in intact cells, suggesting that access of chelated and insoluble forms of Fe(III) and AQDS is restricted in whole cells. Interestingly, the E. coli CymA orthologue NapC also carried ferric reductase activity. Our data support the argument that the biochemical mechanism of Fe(III) reduction per se was not the key innovation leading to environmental relevant DIR bacteria. Rather, the evolution of an extension of the electron transfer pathway from the Fe(III) reductase CymA to the cell surface via a system of periplasmic and outer membrane cytochrome proteins enabled access to diffusion-impaired electron acceptors.
Alternate JournalMol. Microbiol.
0 November 24, 2010