Isolation And Screening Of Actinobacteria From Polar Marine Sediments

Marine sediments are nutrient-rich microbial habitats containing abundant unique marine microorganisms, expecially actinobacteria which are famous for their abilities to produce all kinds of compounds with bioactivities.In this study, actinobacterial strains were isolated from eight sediments of polar marine and identified by the analysis of ARDRA and 16S rDNA sequences. The research of ecological conditions for all isolates has been carried out, as well as secondary metabolite gene amplification and antibacterial activity screening.Using spread-plate technique and the analysis of ARDRA and 16S rDNA sequences, 85 actinobacterial strains were isolated and indentified and were shown to represent strains from 6 genera: Leifsonia,Salinibacterium,Arthrobacter,Rhodococcus,Aeromicrobium and Frigoribacterium. In addition, the isolates ZS314 from the Prydz bay, Antarctica was suggested as a novel Frigoribacterium with the highest 16S rDNA similarity less than 97% to the closest strain.Diversity and quantity of actinobacterial strains isolated from different sediments were different. Leifsonia and Rhodococcus were predominant in actinobacterial strains isolated from Antarctic marine sediments, while Leifsonia and Salinibacterium from Arctic marine sediments. 38 actinobacterial strains from 4 genera isolated from ZS3 collected from Antarctic Zhongshan Station, and the isolation rate was up to 63.33%. However, quantity and isolation rate of actionobacterial strains from KS6 collected from the Arctic region was the worst, only 2 actinobacterial strains isolated and isolation rate was only 20%.In the study of isolation of actinobacterial strains with different culture medium, the results shown that ISP3, ISP5 and mineral agar medium were more suitable to isolate marine actinobacteria, because the quantities, kinds of genera and isolation rates of actinobacterial strains from these medium were high.All tested strains grew better on media prepared with the natural seawater than on those prepared with the deionized water and greatest salt concentration was 10%. In addition, five strains had been shown to have an obligate growth requirement for salt, confirming these strains as bona fide marine organisms. All tested strains could grow at 0℃and most of them were psychrotrophic which grew better at the temperature between 15-25℃. The optimum pH was 7-8, and strains could not grow at pH4 but most of them could grow at pH10.Amplification of PKS I,II and NRPS gene showed that 11 strains contained type I PKS gene, 25 strains contained type II PKS gene, 68 strains contained NRPS gene, and 25 strains contained two genes simultaneously. In addition, three Rhodococcus (ZS350, ZS352, ZS360) contained all the three genes. These positive strains likely to produce valuable metabolites. However, using Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Candida albicans as indicators to test the antimicrobial ability of the actinobacterial strains, no active strains were obtained.