Gut microbiome disruption impairs arsenic biotransformation and exacerbates toxicity in the water flea Daphnia magna

초록

Arsenic risk in waters depends on chemical speciation, yet studies on host-associated microbiota to the in vivo detoxification mechanisms remain unclear. We exposed Daphnia magna for 21 days to inorganic arsenic at 2 mg/L with/without a broad-spectrum antibiotic cocktail that disrupts the gut microbiome. We assessed life-history traits, whole-body arsenic species by HPLC coupled to ICP-MS, and gut community composition by 16S rRNA gene sequencing with LEfSe and PICRUSt2 analyses. Both Arsenic and antibiotics alone impaired growth and reproduction, while co-exposure produced the strongest effects. Microbiome disruption increased total arsenic burden (∼14%) and shifted speciation away from detoxified end-products. Formation of arsenobetaine decreased by an order of magnitude, whereas dimethylarsinic acid approximately doubled. Under arsenic exposure alone, core taxa such as Aeromonas proliferated, accompanied by enrichment of predicted arsenic reductases and methyltransferases. Antibiotic treatment eliminated these taxa, favored Streptococcus , Methylophilus , and Veillonella , and suppressed predicted arsenic-processing functions. These results demonstrate that an intact Daphnia gut microbiome facilitates conversion of inorganic arsenic to less toxic organoarsenicals and mitigates toxicity. Microbiome integrity emerges as a practical control on arsenic fate and hazard in freshwater zooplankton, relevant to risk assessment under antibiotic co-contamination.

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