AUTHOR=Ge Xiaoxuan , Thorgersen Michael P. , Poole Farris L. , Deutschbauer Adam M. , Chandonia John-Marc , Novichkov Pavel S. , Gushgari-Doyle Sara , Lui Lauren M. , Nielsen Torben , Chakraborty Romy , Adams Paul D. , Arkin Adam P. , Hazen Terry C. , Adams Michael W. W. 

TITLE=Characterization of a Metal-Resistant Bacillus Strain With a High Molybdate Affinity ModA From Contaminated Sediments at the Oak Ridge Reservation

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.587127

DOI=10.3389/fmicb.2020.587127

ISSN=1664-302X

ABSTRACT=<p>A nitrate- and metal-contaminated site at the Oak Ridge Reservation (ORR) was previously shown to contain the metal molybdenum (Mo) at picomolar concentrations. This potentially limits microbial nitrate reduction, as Mo is required by the enzyme nitrate reductase, which catalyzes the first step of nitrate removal. Enrichment for anaerobic nitrate-reducing microbes from contaminated sediment at the ORR yielded <italic>Bacillus</italic> strain EB106-08-02-XG196. This bacterium grows in the presence of multiple metals (Cd, Ni, Cu, Co, Mn, and U) but also exhibits better growth compared to control strains, including <italic>Pseudomonas fluorescens</italic> N2E2 isolated from a pristine ORR environment under low molybdate concentrations (&lt;1 nM). Molybdate is taken up by the molybdate binding protein, ModA, of the molybdate ATP-binding cassette transporter. ModA of XG196 is phylogenetically distinct from those of other characterized ModA proteins. The genes encoding ModA from XG196, <italic>P. fluorescens</italic> N2E2 and <italic>Escherichia coli</italic> K12 were expressed in <italic>E. coli</italic> and the recombinant proteins were purified. Isothermal titration calorimetry analysis showed that XG196 ModA has a higher affinity for molybdate than other ModA proteins with a molybdate binding constant (K<sub><italic>D</italic></sub>) of 2.2 nM, about one order of magnitude lower than those of <italic>P. fluorescens</italic> N2E2 (27.0 nM) and <italic>E. coli</italic> K12 (25.0 nM). XG196 ModA also showed a fivefold higher affinity for molybdate than for tungstate (11 nM), whereas the ModA proteins from <italic>P. fluorescens</italic> N2E2 [K<sub><italic>D</italic></sub> (Mo) 27.0 nM, K<sub><italic>D</italic></sub> (W) 26.7 nM] and <italic>E. coli</italic> K12[(K<sub><italic>D</italic></sub> (Mo) 25.0 nM, K<sub><italic>D</italic></sub> (W) 23.8 nM] had similar affinities for the two oxyanions. We propose that high molybdate affinity coupled with resistance to multiple metals gives strain XG196 a competitive advantage in Mo-limited environments contaminated with high concentrations of metals and nitrate, as found at ORR.</p>