A single Vibrionales 16S rRNA oligotype dominates the intestinal microbiome in two geographically separated Atlantic cod populations

Abstract BackgroundHost-microbe interactions are particularly intriguing in Atlantic cod (Gadus morhua), as it lacks the MHC II complex involved in presentation of extracellular pathogens. Nonetheless, little is known about the diversity of its microbiome in natural populations. Here, we use 16S rRNA high-throughput sequencing to investigate the microbial community composition in gut content and mucosa of 22 adult individuals from two coastal populations in Norway, located 470 km apart. ResultsWe identify a core microbiome of 23 OTUs (97% sequence similarity) in all individuals that comprises 93% of the total number of reads. The most abundant orders are classified as Vibrionales, Fusobacteriales, Clostridiales and Bacteroidales. While mucosal samples show significantly lower diversity than gut content samples, no differences in OTU community composition are observed between the two populations. The differential abundance of oligotypes within two common OTUs does reveal limited spatial segregation. Remarkably, the most abundant OTU consists of a single oligotype (order Vibrionales, genus Photobacterium) that represents nearly 50% of the reads in both locations. ConclusionsOur results show that the intestinal bacterial community of two geographically separated coastal populations of Atlantic cod is dominated by a limited number of highly abundant 16S rRNA oligotypes shared by all specimens examined. The ubiquity of these oligotypes suggests that the northern coastal Atlantic cod gut microbiome is colonized by a limited number of species with excellent dispersal capabilities that are well suited to thrive in their host environment.