AUTHOR=Karamash Maksym , Stumpe Michael , Dengjel Jörn , Salgueiro Carlos A. , Giese Bernd , Fromm Katharina M. 

TITLE=Reduction Kinetic of Water Soluble Metal Salts by Geobacter sulfurreducens: Fe2+/Hemes Stabilize and Regulate Electron Flux Rates

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.909109

DOI=10.3389/fmicb.2022.909109

ISSN=1664-302X

ABSTRACT=<p><italic>Geobacter sulfurreducens</italic> is a widely applied microorganism for the reduction of toxic metal salts, as an electron source for bioelectrochemical devices, and as a reagent for the synthesis of nanoparticles. In order to understand the influence of metal salts, and of electron transporting, multiheme <italic>c</italic>-cytochromes on the electron flux during respiration of <italic>G. sulfurreducens</italic>, the reduction kinetic of Fe<sup>3+</sup>, Co<sup>3+</sup>, V<sup>5+</sup>, Cr<sup>6+</sup>, and Mn<sup>7+</sup> containing complexes were measured. Starting from the resting phase, each <italic>G. sulfurreducens</italic> cell produced an electron flux of 3.7 × 10<sup>5</sup> electrons per second during the respiration process. Reduction rates were within ± 30% the same for the 6 different metal salts, and reaction kinetics were of zero order. Decrease of <italic>c</italic>-cytochrome concentrations by downregulation and mutation demonstrated that <italic>c</italic>-cytochromes stabilized respiration rates by variation of their redox states. Increasing Fe<sup>2+</sup>/heme levels increased electron flux rates, and induced respiration flexibility. The kinetic effects parallel electrochemical results of <italic>G. sulfurreducens</italic> biofilms on electrodes, and might help to optimize bioelectrochemical devices.</p>