Biodiversity of culturable bacteria associated with Crassostrea hongkongensis from the tidal flat of Naozhou Island in the South China Sea

Abstract:

[Objective] To investigate the diversity of cultivable bacteria isolated from Crassostrea hongkongensis collected from the tidal flat of Naozhou Island (20°52′–20°56′ N, 110°33′–110°38′ E) in the South China Sea. [Methods] Bacteria strains were isolated from homogenates of the sample by using conventional culture-dependent method, and then the isolated strains were investigated by using a phylogenetic analysis based on the 16S rRNA gene sequences. [Results] We isolated 102 bacteria strains from the sample on a number of media [MA (marine agar 2216), MH (moderate halophilic medium agar), NA (nutrient agar)] supplemented with 0–25% (W/V) NaCl. On the basis of the results of some morphological, physiological and biochemical tests, we selected 74 strains to perform a further phylogenetic analysis. Our results showed that the 74 isolates represented 38 species, belonging to 18 genera (Idiomarina, Morganella, Proteus, Halomonas, Paracoccus, Wohlfahrtiimonas, Marinobacter, Vibrio, Pseudoalteromonas, Shewanella, Oceanimonas, Nitratireductor, Myroides, Bacillus, Virgibacillus, Staphylococcus, Enterococcus, Trichococcus) of 16 families (Idiomarinaceae, Enterobacteriaceae, Halomonadaceae, Rhodobacteraceae, Xanthomonadaceae, Alteromonada- ceae, Vibrionaceae, Pseudoalteromonadaceae, Shewanellaceae, Aeromonadaceae, Phyllobacteriaceae, Flavobacteriaceae, Bacillaceae, Staphylococcaceae, Enterococcaceae, Carnobacteriaceae) in 4 phylogenetic groups (Gamma-Proteobacteria, Alpha-Proteobacteria, Bacteroidetes, Firmicutes). The most of isolates were within the subphylum Gamma-Proteobacteria (45 strains, 60.8%), followed by Firmicutes (12 strains, 16.2%), Bacteriodetes (11 strains, 14.9%) and Alpha-Proteobacteria (6 strains, 8.1%). The phylogenetic analysis results suggested that there were obvious genetic divergences between most isolates and their closest type strains (16S rRNA gene sequence similarities ranged from 94.3% to 99.8%). The results also showed that, out of the 74 isolates, at least 6 strains could represent potential new taxa. Strain JSM 111069 could represent a novel genus in the family Carnobacteriaceae. Strains JSM 111039 and JSM 111085 could represent two novel species of the genus Bacillus, and strains JSM 111020, JSM 111072 and JSM 111090 could represent three novel species within three characterized genera Pseudoalteromonas, Proteus and Idiomarina, respectively. [Conclusion] The results presented above showed that there are abundant bacteria diversity in Crassostrea hongkongensis collected from the tidal flat of Naozhou Island in the South China Sea.