Effect of dietary Bacillus subtilis supplement on Cd toxicokinetics and Cd-induced immune and antioxidant impairment of Procambarus clarkii

Abstract

Abstract Cadmium (Cd), a non-biodegradable contaminant in freshwater ecosystems, can pose a serious threat to aquatic animals at high levels. In this study, the Cd toxicokinetics and the immune and antioxidant defense were explored after the crayfish exposed to different levels of Cd (0, 0.1, 1.0 mg Cd/L) or treated with 1.0 mg Cd/L and dietary Bacillus subtilis supplementation (1 x 107 cfu/g). Results from the 21-day uptake and depuration experiment revealed that Cd exposure elicited a dose-and time-dependent uptake in all crayfish tissues, and the rank order of Cd concentration was: gill > hepatopancreas > exoskeleton > muscle. The two-compartment model demonstrated that gills had the highest ku value after Cd aqueous exposure and the ku and kd values in gill, hepatopancreas, and exoskeleton of the group with 1.0 mg Cd/L were higher than those of the group with low Cd concentration (0.1 mg Cd/L). However, B. subtilis could increase Cd ku and decrease Cd kd in hepatopancreas, resulting in the reduction of BCF, Css and Tb1/2. A positive correlation was found between aqueous Cd concentration and the severity of hepatopancreas histopathological injury, while B. subtilis could ameliorate the pathological damage in the high Cd group. Similarly, Cd aqueous exposure elevated malonaldehyde (MDA) content and suppressed the activities of lysozyme (LZM), acid phosphatase (ACP) and alkaline phosphatase (AKP) in hemolymph. The activities of superoxide dismutase (SOD) and catalase (CAT) in hepatopancreas were also inhibited. Nevertheless, they were all recovered with the dietary addition of B. subtilis. In conclusion, our results indicated that exposure to Cd significantly increased Cd accumulation and toxic damages in crayfish hepatopancreas, while dietary administration of B. subtilis to crayfish significantly decreased Cd accumulation and improved the immune and antioxidant defense, leading to the prevention in toxic effects of Cd.