Gut microbiota perturbation and subsequent oxidative stress in gut and kidney tissues of zebrafish after individual and combined exposure to inorganic arsenic and fluoride.

Chronic exposure to inorganic arsenic (iAs) and fluoride (F) affect gut health and potentially damage organs. The present study investigates the interplay between gut bacteria and oxidative stress (measured by MDA level, GSH level, catalase activity, Nrf2 translocation and expression) in zebrafish exposed to F (NaF 15 ppm) and As (AsO 50 ppb) alone or in combination. Combined exposure to As and F reduced gut bacterial alteration and imposed less oxidative stress compared to F- exposure alone. V3-V4 metagenomic sequencing revealed Pseudomonas, Aeromonas and Plesiomonas genera dominated in As or F treated groups while As+F treated group was enriched in beneficial Lactococcus and Streptococcus genera. Functional KEGG analysis demonstrated treatment-specific changes in bacterial metabolism, host organismal systems, human diseases, as well as cellular processes of microbial community were significantly affected. When Aeromonas sp. isolated from F-treated fish gut, tagged with GFP-vector and fed (~3.2 × 10 CFU/mL) to untreated fish, induced oxidative stress in gut and kidney. Gut bacteria were found to both increase and mitigate iAs or F-toxicity, whereas As+F treatment promoted a protective response. Correlation analysis between gut microbial community at genus level and oxidative stress parameters of gut and kidney, showed Aeromonas and Plesiomonas genera are strongly correlated with oxidative stress (r = 0.5-0.9, p˂0.05). This study identifies microbiome biomarkers of iAs and F toxicity on gut-kidney axis.