Widespread Distribution of the arsO Gene Confers Bacterial Resistance to Environmental Antimony

Abstract

Microbial oxidation of environmental antimonite (Sb(III)) to antimonate (Sb(V)) is an antimony (Sb) detoxification mechanism. Ensifer adhaerens ST2, a bacterial isolate from a Sb-contaminated paddy soil, oxidizes Sb(III) to Sb(V) under oxic conditions by an unknown mechanism. Genomic analysis of ST2 reveals a gene of unknown function in an arsenic resistance (ars) operon that we term arsO. The transcription level of arsO was significantly upregulated by the addition of Sb(III). ArsO is predicted to be a flavoprotein monooxygenase but shows low sequence similarity to other flavoprotein monooxygenases. Expression of arsO in the arsenic-hypersensitive Escherichia coli strain AW3110Δars conferred increased resistance to Sb(III) but not arsenite (As(III)) or methylarsenite (MAs(III)). Purified ArsO catalyzes Sb(III) oxidation to Sb(V) with NADPH or NADH as the electron donor but does not oxidize As(III) or MAs(III). The purified enzyme contains flavin adenine dinucleotide (FAD) at a ratio of 0.62 mol of FAD/mol protein, and enzymatic activity was increased by addition of FAD. Bioinformatic analyses show that arsO genes are widely distributed in metagenomes from different environments and are particularly abundant in environments affected by human activities. This study demonstrates that ArsO is an environmental Sb(III) oxidase that plays a significant role in the detoxification of Sb(III).

Metal-Binding Protein TaGlo1 Improves Fungal Resistance to Arsenite (AsIII) and Methylarsenite (MAsIII) in Paddy Soil

“…For example, the abundance of arsC (As V reductase) and arsM is significantly and positively correlated with the concentration of total As or As III in the soil solution . As III concentration is also positively correlated with the abundance of aoxA (As III oxidase small subunit), aoxB (As III oxidase large subunit), and arsH (arsenical resistance protein) in mining soils …”

“…74 As III concentration is also positively correlated with the abundance of aoxA (As III oxidase small subunit), aoxB (As III oxidase large subunit), and arsH (arsenical resistance protein) in mining soils. 75 Environmental Implications. The co-occurrence of As III and MAs III in paddy soils exacerbates the challenge of mitigating As accumulation in the rice grains.…”

Differential Mechanisms of Microbial As(III) and Sb(III) Oxidation and Their Contribution to Tailings Reclamation

“…Consistently, both anoA -containing strain AsSb1 and anoA -encoding MAGs isolated or retrieved from XKS tailing in this study belong to the same order as the family Rhizobiaceae . Further, multiple known Sb­(III) oxidizers, such as Allorhizobium , Ensifer , Agrobacterium , and Rhizobium , were also affiliated with these lineages. ,− On the other hand, other known Sb­(III) oxidizing populations, such as Thiobacillus and Pseudomonas , may utilize different mechanisms for Sb­(III) oxidation. − For instance, the arsO gene encoding a homologue of flavoprotein monooxygenase was reported to mediate Sb­(III) oxidation in various microorganisms, including Thiobacillus and Pseudomonas . Furthermore, the extracellular superoxide has been shown to mediate Sb­(III) oxidation in Pseudomonas . , These observations suggested that various functional genes may be responsible for Sb­(III) oxidation.…”