Objective: To investigate the diversity of culturable bacteria isolated from the sea urchin Hemicentrotus pulcherrimus collected from a tidal flat of Naozhou Island (20 degrees 52'N - 20 degrees 56'N 110 degrees 33'E - 110 degrees 38'E), Leizhou Bay, South China Sea, China.
Methods: Bacteria were isolated from the sample by using conventional culture-dependent method and then investigated by using phylogenetic analysis based on 16S rRNA gene sequence comparisons.
Results: We isolated 106 bacterial strains from the sample on media (Difco marine 2216, International Streotomyces Project medium 2, nutrient, sea water and humic acid agars) supplemented with 0 - 2 mol/L NaCl. On the basis of morphological, physiological and biochemical characteristics, we selected 34 strains to perform a phylogenetic analysis based on 16S rRNA gene sequences. Our results showed that 34 isolates represented 21 species, belonging to 17 genera (Alteromonas, Bacillus, Brachybacterium, Brevibacterium, Halobacillus, Halomonas, Nocardiopsis, Oceanobacillus, Piscibacillus, Planococcus, Pontibacillus, Pseudoalteromonas, Pseudonocardia, Salinicoccus, Salinivibrio, Staphylococcus, Vibrio, Virgibacillus) of 10 families (Alteromonadaceae, Bacillaceae, Brevibacteriaceae, Dermabacteraceae, Halomonadaceae, Planococcaceae, Pseudoalteromonadaceae, Pseudonocardiaceae, Nocardiopsaceae, Staphylococcaceae, Vibrionaceae) in three phylogenetic groups (Actinobacteria, Firmicutes, Gamma-Proteobacteria). The most abundant and diverse isolates were within the phylum Firmicutes (58.8%) and the subphylum Gamma-Proteobacteria (26.5%). The phylogenetic distance matrix results suggested that there were obvious genetic divergences between most isolates and their closestly related type strains (16S rRNA gene sequence similarities ranged from 99.6 to 99.9%), and that, out of 34 isolates, at least 5 strains (JSM 076033, JSM 076056, JSM 076093, JSM 078063, JSM 078169) could represent 5 potential new species within 5 characterized genera (Jeotgalicoccus, Pontibacillus, Halomonas, Bacillus, Sporosarcina), in which the descriptions of 3 novel species [Jeotgalicoccus marinus (type strain, JSM 076033), Pontibacillus halophilus (JSM 076056), Halomonas zhanjiangensis (JSM 078169)] have been published in IJSEM (International Journal of Systematic and Evolutionary Microbiology).
Conclusion: The results presented above showed that there are abundant bacteria diversity in the sea urchin Hemicentrotus pulcherrimus collected from Naozhou Island.