Comparative Analyses of Scylla Olivacea Gut Microbiota Composition and Function Suggest the Capacity for Polyunsaturated Fatty Acid Biosynthesis

Abstract Multiple studies have linked lipid metabolism with intestinal bacterial structure in aquatic organisms. However, the possibility of the gut microbiota participating in synthesizing beneficial long-chain polyunsaturated fatty acid (LC-PUFA) remains vague. We profiled the gut microbiota of mud crab Scylla olivacea fed with either a LC-PUFA rich diet (FO), a LC-PUFA-poor but C18-PUFA substrate rich diet (LOCO), and diet with a similar profile as LOCO but with the inclusion of an antibiotic, oxolinic acid. Additionally, the microbiota of wild-caught S. olivacea was also analyzed. Compared to diet FO treatment, crabs fed diet LOCO contain a higher proportion of Proteobacteria, represented by Vibrio and Shewanella, two known taxonomy groups with PUFA biosynthesis capacity. Annotation of metagenomic datasets also suggests functional contribution by these two genera in terms of the KEGG pathway of unsaturated fatty acids biosynthesis and the keto-acyl synthase domains in the microbiota of LOCO treatment. Diet LOCOAB impeded the presence of Vibrio and Shewanella within the gut, and concurrently, the abundance of PUFA biosynthesis pathway-related genes. However, there was an increase in the function of short-chain fatty acids production within this diet, which was accompanied by a shift towards the abundance of phyla Bacteroidota and Spirochaetota, represented by Sunxiuqinia and Carboxylicivirga and Sediminispirochaeta, respectively. Collectively, these results exemplified bacterial communities and their corresponding PUFA biosynthesis pathways in the microbiota of a farmed crustacean species.