AUTHOR=Acosta-Grinok Mauricio , Vázquez Susana , Guiliani Nicolás , Marín Sabrina , Demergasso Cecilia 

TITLE=Looking for the mechanism of arsenate respiration of Fusibacter sp. strain 3D3, independent of ArrAB

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1029886

DOI=10.3389/fmicb.2022.1029886

ISSN=1664-302X

ABSTRACT=<p>The literature has reported the isolation of arsenate-dependent growing microorganisms which lack a canonical homolog for respiratory arsenate reductase, ArrAB. We recently isolated an arsenate-dependent growing bacterium from volcanic arsenic-bearing environments in Northern Chile, <italic>Fusibacter</italic> sp. strain 3D3 (<italic>Fas</italic>) and studied the arsenic metabolism in this Gram-positive isolate. Features of <italic>Fas</italic> deduced from genome analysis and comparative analysis with other arsenate-reducing microorganisms revealed the lack of ArrAB coding genes and the occurrence of two <italic>arsC</italic> genes encoding for putative cytoplasmic arsenate reductases named ArsC-1 and ArsC-2. Interestingly, ArsC-1 and ArsC-2 belong to the thioredoxin-coupled family (because of the redox-active disulfide protein used as reductant), but they conferred differential arsenate resistance to the <italic>E. coli</italic> WC3110 Δ<italic>arsC</italic> strain. PCR experiments confirmed the absence of <italic>arrAB</italic> genes and results obtained using uncouplers revealed that <italic>Fas</italic> growth is linked to the proton gradient. In addition, <italic>Fas</italic> harbors ferredoxin-NAD<sup>+</sup> oxidoreductase (Rnf) and electron transfer flavoprotein (<italic>etf</italic>) coding genes. These are key molecular markers of a recently discovered flavin-based electron bifurcation mechanism involved in energy conservation, mainly in anaerobic metabolisms regulated by the cellular redox state and mostly associated with cytoplasmic enzyme complexes. At least three electron-bifurcating flavoenzyme complexes were evidenced in <italic>Fas</italic>, some of them shared in conserved genomic regions by other members of the <italic>Fusibacter</italic> genus. These physiological and genomic findings permit us to hypothesize the existence of an uncharacterized arsenate-dependent growth metabolism regulated by the cellular redox state in the <italic>Fusibacter</italic> genus.</p>