Hypoimmunity and intestinal bacterial imbalance are closely associated with blue body syndrome in cultured Penaeus vannamei

Scientific evidence is increasing that intestinal microbial flora is closely related to organism health and immunity. The relationship between the shrimp midgut microbial community and blue body syndrome is, however, unclear. In this study, we collected midgut and seawater samples from ponds with healthy and diseased shrimp to understand variations in bacterial communities in the midguts of healthy or diseased shrimp from the same habitat. The expression level of penaeidin, lectin, crustins, and defensin in shrimp with blue body syndrome were decreased, compared to those of healthy shrimp, indicating that shrimp with blue body syndrome have a lower autoimmune. 16 s sequencing analysis found that total 37 phyla, 91 classes, 160 orders, 221 families and 373 genera was detected. Among them, Proteobacteria (55.7%), Cyanobacteria (30.5%), Bacteroides (5.4%), Actinomycetes (1.1%) and Trichomes (0.9%) are the core bacteria in the intestinal bacteria of Penaeus vannamei. The intestinal bacterial communities are closely associated with the severity of shrimp disease. This pattern was further evidenced by NMDS and LEfSe analyses that were significantly different in abundance between healthy and diseased shrimp. In addition, we found that within a given bacterial genus, the patterns of enrichment or decrease were inconsistent with the known probiotics functions of those bacteria. These results suggested that the composition disorders and immunity decrease of intestinal microbiota were closely associated with shrimp blue body syndrome. Moreover, the identified bacterial genus can be used as an indicator taxa to evaluate the occurrence probability of blue body syndrome in shrimp.