Accumulation of microcystins, bacterial community composition and mlrA gene abundance in shrimp culture ponds

Cyanobacteria blooms occur frequently in low-salinity shrimp culture ponds. To provide useful information about the potential harm and in situ biodegradation pathway of microcystins (MCs) in these ponds, we investigated accumulation of MCs in shrimp hepatopancreas and sediments, bacterial community composition and mlrA gene abundance in intestines and sediments in 11 Litopenaeus vannamei culture ponds from 9 farms in China. MCs (MC-LR, MC-RR and MC-YR) accumulated in shrimp hepatopancreas and sediments in each sampled pond. Higher bacterial richness and diversity were observed in sediments than in intestines. Two MC-degrading genera (Sphingobium and Roseomonas) were detected in the intestine bacterial community, and 3 MC-degrading genera (Sphingobium, Rhizobium and Acinetobacter) were detected in the sediment bacterial community. The mlrA gene was easier to detect and more abundant in shrimp intestines than in sediments. These results suggest that there was a potential MC hazard in shrimp culture ponds, and the biodegradation pathway in shrimp intestines seemed to be more dependent on the mlr pathway than that in the sediments.