Bioprospecting Of Actinobacteria Resource Of Endophytic Actinobacteria Isolated From Eumangroves Collected In Dongzhaigang Of Hainan Province

[Objective] To study the diversity and bioactivity of actinobacteria isolated from Mangroves in Dongzhaigang, Hainan. [Methods] Various tissues from 14 kinds of mangrove plants as samples were collected from Dongzhaigang National Nature Reserve in Hainan, China. Samples were ground into powders after surface sterilization and cultured on 10 different media for strain isolation. To determine the phylogenetic position of the strains,16S rRNA gene sequences were obtained by PCR amplification and direct sequencing, then compared with gene database. The antifungal and antibacterial activities of the crude extracts were tested by disk diffusion method. Screening of PKS I, PKS II and NRPS genes was carried out by PCR and agarose electrophoresis. [Results] 146 strains affiliated to 18 genera were obtained. The dominant genus is Streptomyces. The highest similarity of 16S rRNA gene sequences between strain S3Cf-2 and the validly described species Couchioplanes caerw/eusDSM44103T, between strain S3Af-1 and the validly described species Microlunatus terrae BS6T was 97.45% and 97.43%, respectively, strain S3Af-lT was proved to be a novel species of the genus Microlunatus, for which the name Microlunatus endophyticus sp. nov. is proposed. The antimicrobial activity of crude extracts from the fermentation broths were tested against different pathogenic microorganisms by paper-disc diffusion method. Antimicrobial test showed that 40 out of 46 strains exhibited positive results in at least one antifungal or antibacterial assay, and the total positive rate was 86.96%. The results showed that the strain S3Cf-2 inhibited the growth of Staphylococcus aureus and Enterococcus faecalis, meanwhile, the strain S3 Af-1 inhibited only the growth of Staphylococcus aureus. The diameter of inhibitory zone from strain S3Cf-2 against Staphylococcus aureus can reach to 28mm. Thirty eight in 40 strains with antimicrobial activity, probably, had at least one antibiotic biosynthetic gene including NRPS, PKS I and PKS II, and 14 strains have all the three kinds of biosynthetic genes of antibiotics. [Conclusion] The study demonstrates that diversity of endophytic actinobacteria from mangrove are rich and mangrove tissues as a special niche for discovery of new pharmaceutical microorganisms are waiting to be explored.