AUTHOR=Coursolle Dan , Gralnick Jeffrey A.

TITLE=Reconstruction of Extracellular Respiratory Pathways for Iron(III) Reduction in Shewanella Oneidensis Strain MR-1

JOURNAL=Frontiers in Microbiology

VOLUME=3

YEAR=2012

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00056

DOI=10.3389/fmicb.2012.00056

ISSN=1664-302X

ABSTRACT=<p><italic>Shewanella oneidensis</italic> strain MR-1 is a facultative anaerobic bacterium capable of respiring a multitude of electron acceptors, many of which require the Mtr respiratory pathway. The core Mtr respiratory pathway includes a periplasmic <italic>c</italic>-type cytochrome (MtrA), an integral outer-membrane β-barrel protein (MtrB), and an outer-membrane-anchored <italic>c</italic>-type cytochrome (MtrC). Together, these components facilitate transfer of electrons from the <italic>c</italic>-type cytochrome CymA in the cytoplasmic membrane to electron acceptors at and beyond the outer-membrane. The genes encoding these core proteins have paralogs in the <italic>S. oneidensis</italic> genome (<italic>mtrB</italic> and <italic>mtrA</italic> each have four while <italic>mtrC</italic> has three) and some of the paralogs of <italic>mtrC</italic> and <italic>mtrA</italic> are able to form functional Mtr complexes. We demonstrate that of the additional three <italic>mtrB</italic> paralogs found in the <italic>S. oneidensis</italic> genome, only MtrE can replace MtrB to form a functional respiratory pathway to soluble iron(III) citrate. We also evaluate which <italic>mtrC</italic>/<italic>mtrA</italic> paralog pairs (a total of 12 combinations) are able to form functional complexes with endogenous levels of <italic>mtrB</italic> paralog expression. Finally, we reconstruct all possible functional Mtr complexes and test them in a <italic>S. oneidensis</italic> mutant strain where all paralogs have been eliminated from the genome. We find that each combination tested with the exception of MtrA/MtrE/OmcA is able to reduce iron(III) citrate at a level significantly above background. The results presented here have implications toward the evolution of anaerobic extracellular respiration in <italic>Shewanella</italic> and for future studies looking to increase the rates of substrate reduction for water treatment, bioremediation, or electricity production.</p>