Diversity of autochthonous bacterial communities in the intestinal mucosa of grass carp (Ctenopharyngodon idellus) (Valenciennes) determined by culture-dependent and culture-independent techniques

Traditional culture-based technique and 16S rDNA sequencing method were used to investigate the mucosa-associated autochthonous microbiota of grass carp (Ctenopharyngodon idellus). Twenty-one phylotypes were detected from culturable microbiota, with Aeromonas, Shewanella, Lactococcus, Serratia, Brevibacillus, Delftia, Pseudomonas, Pantoea, Enterobacter, Buttiauxella and Yersinia as their closest relatives. Genomic DNA was directly extracted from the gut mucosa of C. idellus originating from six different geographical regions, and used to generate 609 random bacterial clones from six clone libraries and 99 archaeal clones from one library, which were grouped into 67 bacterial and four archaeal phylotypes. Sequence analysis revealed that the intestinal mucosa harboured a diversified bacterial microbiota, where Proteobacteria, Firmicutes and Bacteroidetes were dominant, followed by Actinobacteria, Verrucomicrobia and Deinococcus-Thermus. The autochthonous bacterial communities in the gut mucosa of fish from different aquatic environments were not similar (C-s < 0.80), but gamma-Proteobacteria was a common bacterial class. In comparison to bacterial communities, the archaeal community obtained from one library consisted of Crenarchaeota and Euryarchaeota. These results demonstrate that molecular methods facilitate culture-independent studies, and that fish gut mucosa harbours a larger bacterial diversity than previously recognized. The grass carp intestinal habitat selects for specific bacterial taxa despite pronounced differences in host environments.