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

ACOSTA-GRINOK, MAURICIO; VÁZQUEZ, SUSANA; GUILIANI, NICOLÁS; MARÍN, SABRINA; DEMERGASSO, CECILIA

Frontiers in Microbiology

Frontiers

Año: 2022 vol. 13

Theliterature has reported the isolation of arsenate-dependent growingmicroorganisms which lack a canonical homolog for respiratory arsenatereductase, ArrAB. We recently isolated an arsenate-dependent growing bacteriumfrom volcanic arsenic-bearing environments in Northern Chile, Fusibacter sp.strain 3D3 (Fas) and studied the arsenic metabolism in this Gram-positiveisolate. Features of Fas deduced from genome analysis and comparative analysiswith other arsenate-reducing microorganisms revealed the lack of ArrAB codinggenes and the occurrence of two arsC genes encoding for putative cytoplasmicarsenate reductases named ArsC-1 and ArsC-2. Interestingly, ArsC-1 and ArsC-2belong to the thioredoxin-coupled family (because of the redox-active disulfideprotein used as reductant), but they conferred differential arsenate resistanceto the E. coli WC3110 ΔarsC strain. PCR experiments confirmed the absence ofarrAB genes and results obtained using uncouplers revealed that Fas growth islinked to the proton gradient. In addition, Fas harbors ferredoxin-NAD+oxidoreductase (Rnf) and electron transfer flavoprotein (etf) coding genes.These are key molecular markers of a recently discovered flavin-based electronbifurcation mechanism involved in energy conservation, mainly in anaerobicmetabolisms regulated by the cellular redox state and mostly associated withcytoplasmic enzyme complexes. At least three electron-bifurcating flavoenzymecomplexes were evidenced in Fas, some of them shared in conserved genomicregions by other members of the Fusibacter genus. These physiological andgenomic findings permit us to hypothesize the existence of an uncharacterizedarsenate-dependent growth metabolism regulated by the cellular redox state inthe Fusibacter genus.