Bacterioplankton assemblages as biological indicators of shrimp health status

The close correlation between the incidence of shrimp disease and the surrounding microbial community is well established. However, it remains uncertain whether particular bacterial assemblages are indicative of shrimp health status (healthy or diseased). To test this hypothesis, we used 454 pyrosequencing to compare the bacterioplankton composition of ponds with healthy shrimp populations (PHS) with that of ponds with diseased shrimp populations (PDS). The results showed that the bacterial communities in PDS were markedly distinct (P < 0.05) from those of PHS but that the diversity was unchanged. This sudden shift in the bacterioplankton communities was accompanied by severe mass mortality of the shrimp. The differentiation of the bacterial communities was primarily shaped by the total phosphate and by the chemical oxygen demand. In particular, we identified 11 indicator orders (in which 6 for healthy status and 5 for diseased status) that differentiated PHS from PDS. In a given pond, especially, the sum of the relative abundance of the disease indicator phylotypes and that of the healthy indicator phylotypes could be used to estimate the health status of the pond. This result suggests that the bacterioplankton composition determines, at least in part, the health status of the shrimp. Overall, this study provides direct evidence that the composition of the bacterioplankton community can serve as a biological indicator to evaluate the occurrence of shrimp diseases.