Anoxygenic phototrophic arsenite oxidation by a Rhodobacter strain

Abstract

Microbially mediated arsenic redox transformations are key for arsenic speciation and mobility in rice paddies. Whereas anaerobic anoxygenic photosynthesis coupled to arsenite (As(III)) oxidation has been widely examined in arsenic‐replete ecosystems, it remains unknown whether this light‐dependent process exists in paddy soils. Here, we isolated a phototrophic purple bacteria, Rhodobacter strain CZR27, from an arsenic‐contaminated paddy soil and demonstrated its capacity to oxidize As(III) to arsenate (As(V)) using malate as a carbon source photosynthetically. Genome sequencing revealed an As(III)‐oxidizing gene cluster (aioXSRBA) encoding an As(III) oxidase. Functional analyses showed that As(III) oxidation under anoxic phototrophic conditions correlated with transcription of the large subunit of the As(III) oxidase aioA gene. Furthermore, the non‐As(III) oxidizer Rhodobacter capsulatus SB1003 heterologously expressing aioBA from strain CZR27 was able to oxidize As(III), indicating that aioBA was responsible for the observed As(III) oxidation in strain CZR27. Our study provides evidence for the presence of anaerobic photosynthesis‐coupled As(III) oxidation in paddy soils, highlighting the importance of light‐dependent, microbe‐mediated arsenic redox changes in paddy arsenic biogeochemistry.

Genome sequence and characterisation of a freshwater photoarsenotroph, Cereibacter azotoformans strain ORIO, isolated from sediments capable of cyclic light–dark arsenic oxidation and reduction

“…The latter study used PCR to detect the presence and expression of arsC and aioA but did not report a genome sequence or screen for the presence of an arxA gene. Wu et al (2023) recently described the isolation, physiology and genomics of an aio-containing Rhodobacter strain (CZR27) from rice paddy sediments. Strain CZR27 anaerobically oxidised As(III) to As(V) photosynthetically with malate as the carbon source.…”