| To understand the diversity of culturable bacteria isolated from a sea urchin (Hemicentrotus pulcherrimus) collected from the coastal sea water area of Naozhou Island (20°52′N～20°56′N 110°33′E～110°38′E) in the Leizhou Bay on South China Sea, bacteria were isolated by using conventional culture-dependent method and investigated by means of phylogenetic analysis based on 16S rRNA gene sequence comparisons. And the antimicrobial activities of the fermentation broth extracts from the isolates were detected on 8 sensitive microorganisms in order to find some isolates exhibiting strong bioactivity to be further used in exploitation.We isolated 106 bacterium 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 some 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%). Shannon-winner indexe (H) was 4.24, and Pielou evenness index (E) was 0.97. 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, Pontibacillu, Halomonas, Bacillus, Sporosarcina). The results showed that there are abundant bacteria diversity and evenness in the sea urchin Hemicentrotus pulcherrimus collected from Naozhou Island.The antimicrobial activities of the fermentation brothes from 106 marine bacteria, were further screened by using the cylinder-plate method on 8 indicator microorganisms, i.e. three Gram-positive bacteria (Bacillus subtilis, Sarcina lutea, Staphylococcus aureus), three Gram-negative bacteria (Aerobacter aerogenes, Escherichia coli, Proteus vulgaris) and two fungi (Asperillus niger, Candida albican). The results showed that, out of 106 test strains, 59 were positive in antimicrobial activity (55.7%), in which 10 strains exhibited strong antimicrobial activity. These 10 strains were submitted for 16S rRNA gene amplification and phylogenetic analysis after a number of phenotypic characterization including morphological, biochemical and physiological tests. The results suggested that the 10 strains belonged to the genera Halobacillus (JSM 076017, JSM 076029, JSM 076062), Bacillus (JSM 076009, JSM 076053), Pontibacillus (JSM 076056), Planococcus (JSM 076050), Jeotgalibacillus (JSM 076100), Salinicoccus (JSM 076102) and Serratia (JSM 076077) within the phyla Firmicutes and Proteobacteria.On the basis of the phylogenetic analysis, phenotypic distinctiveness, chemotaxonomic data and DNA-DNA relatedness, 3 strains were proposed to represent 3 novel species within 3 characterized genera., i.e. Jeotgalicoccus marinus sp. nov., with JSM 076033T (=CCTCC AA 207028T =DSM 19772T =KCTC 13189T) as the type strain; Pontibacillus halophilus sp.nov., with JSM 076056T (=CCTCC AA 207029T =DSM 19796T =KCTC 13190T) as the type strain; Halomonas zhanjiangensis sp. nov., with JSM 078169T (=CCTCC AB 208031T =DSM 21076T =KCTC 22279T) as the type strain. The articles describing these new taxa have been published in international journals, i.e. IJSEM (International Journal of Systematic and Evolutionary Microbiology) and Antonie van Leeuwenhoek (Antonie van Leeuwenhoek International Journal of General and Molecular Microbiology).In conclusion, the results presented above showed that there are abundant bacterial diversity and a number of potential new taxa in the sea urchin (Hemicentrotus pulcherrimus) collected from the coastal sea water area of Naozhou Island in the Leizhou Bay on South China Sea, and that these strains are important resources for bioactive compounds.
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