Concurrent methylation and demethylation of arsenic by fungi and their differential expression in the protoplasm proteome

•Transformation and migration change As toxicity and jeopardize human health.•DMA(V) and inorganic As were detected in fungal cells after MMA(V) exposure.•Concurrent methylation and demethylation of As was observed in fungal cells.•Different As exposure triggers the differential expression of proteomic proteins.•R7YMH0 donating a methyl group for SAM was up-regulated after MMA(V) exposure.

Microbial methylation and demethylation are central to arsenic's (As) biogeochemical cycling. Here, the transformations of monomethylarsonic acid (MMA(V)) (50 mg L−1) for 15 days in cells of As-methylating fungi, Fusarium oxysporum CZ-8F1, Penicillium janthinellum SM-12F4, and Trichoderma asperellum SM-12F1, were evaluated, and trace concentrations of As(III) and As(V) were observed in fungal cell extracts. Trace amounts of DMA(V) were also detected in MMA(V) and P. janthinellum SM-12F4 incubations. In situ X-ray absorption near edge structure (XANES) indicated that after exposure to MMA(V) (500 mg L−1) for 15 days, 28.6-48.6% of accumulated As in fungal cells was DMA(V), followed by 18.4-30.3% from As(V), 0-28.1% from As(III), and 4.8-28.9% from MMA(V). The concurrent methylation and demethylation of As occurs in fungal cells. Furthermore, a majority of proteins involved in metabolism, transport, ATP activity, biosynthesis, signal transduction, DNA activity, translation, and oxidative stress were upregulated in T. asperellum SM-12F1 cells after MMA(V) exposure compared to As(III), As(V), and DMA(V). The detoxification process of T. asperellum SM-12F1 was As species-specific. Methylenetetrahydrofolate reductase (R7YMH0) donation of a methyl group for S-adenosylmethionine (SAM) generation significantly increased following MMA(V) exposure.

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