The predominant gut microbiota in the grass puffer, Takifugu alboplumbeus, captured in both river and marine environments

The grass puffer, Takifugu alboplumbeus, a euryhaline fish species, was collected from both river and marine environments, and the gut microbiota of these specimens was examined using clone library analysis and qPCR technology. The results indicated that Aliarcobacter sp. constituted 27.3-96.9% of the three 16S rDNA libraries for river pufferfish and 40.6-86.8% of the three libraries for saltwater pufferfish, indicating that this bacterium is the dominant organism in both river and saltwater pufferfish. Furthermore, Brevinema sp., Mucinivorans sp., Mycoplasma sp., Pseudomonas mosselii, and unclassified members of Desulfovibrionaceae family were detected in both river and saltwater pufferfish at frequencies of 50-83%. In contrast, Ilumatobacter fluminis, Ilumatobacter spp., Nitrincola sp., Tropicibacter alexandrii, and unclassified members of the Microthrixaceae and Mycoplasmataceae families, as well as the Mollicutes class, were detected only from river pufferfish, while Vibrio spp. were detected only in two out of three libraries of saltwater pufferfish. However, qPCR for Vibrionaceae showed that the abundance of Vibrionaceae in the gut of river pufferfish was significantly lower than in saltwater pufferfish, although neither was the predominant bacteria. These results indicate that river and saltwater pufferfish have different gut microbiota. This suggests that the differences in the gut microbiota between river and saltwater pufferfish may be related to the differences in salt tolerance of the gut bacteria, as well as the differences in the environmental microbiota of river and marine waters.