Succeed to culture a novel lineage symbiotic bacterium of Mollicutes which widely found in arthropods intestine uncovers the potential double-edged sword ecological function

Symbiotic gut bacteria play crucial role in host health. Symbionts are widely distributed in arthropod intestines, but their ecological functions are poorly understood due to the inability to cultivate them. Members of Candidatus Bacilliplasma (CB) are widely distributed in crustacean intestine and maybe commensals with hosts, but the paucity of pure cultures has limited further insights into their physiologies and functions. Here, four strains of representative CB bacteria in shrimp intestine were successfully isolated and identified as members of a novel Order in the Phylum Mycoplasmatota. Through genome assembly, the circular genome maps of the four strains were obtained, and the number of coding genes ranged from 1,886 to 1,980. Genomic analysis suggested that the bacteria were missing genes for many critical pathways including the TCA cycle and biosynthesis pathways for amino acids and coenzyme factors. The analysis of 16S amplification data showed that Shewanella, Pseudomonas and CB were the dominant at the genera level in the intestine of Penaeus vannamei. Ecological functional experiments revealed that the strains were symbionts and colonized shrimp intestines. Our valued findings can greatly enhance our understanding and provides new insights into the potentially significant role of uncultured symbiotic bacteria in modulating host health

Acute hypoxia stress mediates HIF-1α-Yki-Cactus axis to facilitate the infection of Vibrio parahaemolyticus in Litopenaeus vannamei

IntroductionHypoxia stress renders aquatic animals more susceptible to bacterial disease, yet the underlying mechanism remains elusive.MethodsWe conducted an acute hypoxia stress experiment to investigate the impact of stress on the immune response of Litopenaeus vannamei via transcriptome analysis, RT-qPCR and Western blot.ResultsOur results showed that acute hypoxia stress disrupted the tissue architecture, and significantly changed the gene expression profiles in the hepatopancreas of shrimp. More importantly, acute hypoxia stress significantly changed the expression levels of immune-related genes. Ladderlectin, GBP 1, Caspase-1, CLEC4F, MR1 and GBP 2 were significantly down-regulated, but HIF-1α, Cactus, TIPE, Akirin-2, Ivns1abp and TLR3 were significantly up-regulated. We further demonstrated that acute hypoxia activated Yki via HIF-1α to enhance expression level of Cactus, and then Cactus inhibited the phosphorylation of Dorsal and its nuclear translocation, thereby suppressing antibacterial immunity. Subsequently, the challenge experiment following stress revealed that exposure to acute hypoxia stress amplified the infectivity and lethality of Vibrio parahaemolyticus to shrimp. The mechanism of HIF-1α-Yki-Cautus axis provided an explanation for this phenomenon.DiscussionThis study offered new insights into interactions among environmental hypoxia stress, host immunity and pathogens, thereby providing practical guidelines for optimizing shrimp culture practices

Bacterial Infection Disrupts the Intestinal Bacterial Community and Facilitates the Enrichment of Pathogenic Bacteria in the Intestines of Penaeus vannamei

Pathogenic infections can reshape the intestinal microbiota of aquatic animals, thereby impacting their health status. In this study, we aimed to investigate whether Vibrio parahaemolyticus infection induces dysbiosis in the intestinal bacterial community of Penaeus vannamei and to assess the associated ecological risks. Our findings revealed the deterministic processes in intestinal bacterial community assembly during bacterial infections, indicating that host selection, i.e., host immune response post-infection, has a significant influence on intestinal microbes. More importantly, we found that bacterial infection reshaped the intestinal community by reducing the relative abundance of probiotic Ruegeria species (e.g., R. atlantica, R. lacuscaerulensis, R. conchae, R. profundi, R. arenilitoris, R. pomeroyi) and increasing the relative abundance of Vibrio species (V. harveyi, V. sinaloensis, V. coralliilyticus, and V. brasiliensis). Significant negative correlations were observed between the relative abundance of these Ruegeria species and the relative abundance of Vibrio species. Moreover, the control P. vannamei contained a substantially higher number of keystone species belonging to Ruegeria in the bacterial community network, whereas bacterial infection individuals had few or no keystone species belonging to Ruegeria, with keystone species belonging to Vibrio becoming more prominent. Thus, the significant increase in Vibrio species abundance in the P. vannamei intestine following bacterial infection was associated with the marked reduction in Ruegeria species. Our findings will provide valuable insights into the complex interactions among bacterial infection, intestinal microbiota, and host health, and they provide guidance for the development of probiotics in promoting the healthy culture of P. vannamei