title: CymA and Exogenous Flavins Improve Extracellular Electron Transfer and Couple It to Cell Growth in Mtr-Expressing Escherichia coli.
abstract: Introducing extracellular electron transfer pathways into heterologous organisms offers the opportunity to explore fundamental biogeochemical processes and to biologically alter redox states of exogenous metals for various applications. While expression of the MtrCAB electron nanoconduit from Shewanella oneidensis MR-1 permits extracellular electron transfer in Escherichia coli, the low electron flux and absence of growth in these cells limits their practicality for such applications. Here we investigate how the rate of electron transfer to extracellular Fe(III) and cell survival in engineered E. coli are affected by mimicking different features of the S. oneidensis pathway: the number of electron nanoconduits, the link between the quinol pool and MtrA, and the presence of flavin-dependent electron transfer. While increasing the number of pathways does not significantly improve the extracellular electron transfer rate or cell survival, using the native inner membrane component, CymA, significantly improves the reduction rate of extracellular acceptors and increases cell viability. Strikingly, introducing both CymA and riboflavin to Mtr-expressing E. coli also allowed these cells to couple metal reduction to growth, which is the first time an increase in biomass of an engineered E. coli has been observed under Fe2O3 (s) reducing conditions. Overall, this work provides engineered E. coli strains for modulating extracellular metal reduction and elucidates critical factors for engineering extracellular electron transfer in heterologous organisms.
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Jensen
authors.affiliation: California Institute for Quantitative Biosciences, University of California , Berkeley, California 94720, United States.
authors.forename: Michaela A
authors.initials: MA
authors.lastname: TerAvest
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Kokish
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Synthetic Biology Institute , Berkeley, California 94720, United States.
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Ajo-Franklin
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism; D005415:Flavins / Q000378:metabolism / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D005818:Genetic Engineering / Q000379:methods*; D007501:Iron / Q000378:metabolism; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012256:Riboflavin / Q000378:metabolism / Q000494:pharmacology*; D020592:Shewanella / Q000235:genetics / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D003574:Cytochrome c Group; D005290:Ferric Compounds; D005415:Flavins; C100938:MtrA protein, Bacteria; D011994:Recombinant Proteins; C000499:ferric oxide; C025314:ferric citrate; C017165:cytochrome c(3); D007501:Iron; C433527:MtrC protein, Shewanella; D012256:Riboflavin
keywords: bioelectrochemical systems; dissimilatory metal-reducing bacteria; energy conservation; multiheme cytochrome c; synthetic biology