Isolation And Characterization Of Marine Actinobacteria And Screening Of Type Ⅰ Polyketide Synthase Sequences

Marine actinobacteria were screened from the sediment samples collected from various sites of Dalian Sea aera. Five different pre-treatment methods were employed and sixteen selective media were used for the isolation of actinobacteria. Totally 447 actinobacterial strains were isolated, and the the dispersion and differential centrifugation (DDC) procedure was revealed to be the most efficient pretreatment method, which remarkedly improved the colony numbers obtained from the sediment samples.Using agar diffusion method, the antimicrobial activities of the actinobacterial isolates were investigated. Totally 197 active strains were identified, 44% of the whole isolates. Interesting isolates with either rare phenotype or strong antimicrobial activities were further studied for the morphological characteristics, the cultural characteristics as well as the physiological and biochemical features. The 16S rDNA of nine strains were sequenced, two of which were identified as Micromonospora strains, analysis, while other seven strains were marine Streptomycetes.Marine Streptomycete S187 was selected for further characterization. Agar diffusion assay of this isolate revealed a broad spectrum of antimicrobial activities, especially potent activities against Psedomonas aeruginosa and Candida albicans. On the baisi of growth, cultural, phenotypic and the physiological-biochemical traits, S187 was suggested to be a novel marine Streptomycete.Type I polyketide synthase (PKSI) gene sequences were screened in 40 strains with either excellent antimicrobial activities or special phenotypes using three sets of degenerate primers designed for the ketosynthase (KS) domain. Five sequenced fragments were identified as new PKSI sequences. Two sequences exhibited highest homology in amino acid level to DfnJ (99%, 70%) from newly reported plant growth promoting Bacillus amyloliquefaciens strain FZB42, and one sequence was closest to BaeN (98%) from the same Bacillus strain. Other two sequences exhibited 73% identity to MerC involved in meridamycin biosynthesis and 98% identity to FscD related to for the biosynthesis of polyene complex FR-008 respectively. The presented studies revealed that abundant marine actinomycete resources exist in the sediment samples in Dalian sea area, at the same time, many isolated strains are potential producers for antimicrobial agents as well as typeI polyketides. These results provided useful information for further exploration of marine actinobacteria resources in Dalian Sea area.