An aquatic probiotic alleviates lead toxicity in grass carp (Ctenopharyngodon idella) via improved intestinal barrier function and reduced Pb bioaccumulation.

Probiotics have been used to mitigate heavy metals (HMs) toxicity, however, the mechanisms by which they alleviate HMs toxicity by regulating intestinal microbiota remain unclear in aquatic animals. In this study, the aquatic probiotic Rhodobacter sphaeroides SC01 (RSSC01) was supplemented in the diet of grass carp to investigate its roles in alleviating lead (Pb) toxicity. The results showed that RSSC01 significantly reduced Pb content in the intestine, gills, and kidneys by 25.27%, 55.83%, and 47.42%, respectively, compared with Pb exposure alone. Additionally, it effectively conferred Pb-induced structural damage to the intestine, liver, and kidney. RSSC01 also greatly increased red blood cell count, hemoglobin content, and aminolevulinic acid dehydratase (ALAD) activity. Based on absolute quantification of microbiome sequencing, RSSC01 was found to colonize the intestine and upregulate the absolute abundance of Pb-adsorbing bacteria (Staphylococcus sciuri, Rhodobacter, Chelatococcus, Shinella) and bile acid-transforming bacteria (Clostridium sensu stricto, Streptococcus, Lactobacillales, and Beijerinckiaceae). Correlation analysis showed that these microbiota regulation enhanced the expression of intestinal tight junction proteins, hepatic SOD activity and MDA content. Taken together, these findings demonstrate that RSSC01 effectively mitigates Pb toxicity in grass carp through regulation of intestinal microbiota.