Isolation and antimicrobial bioactivity of algae-associated actinomycetes from Xisha Islands

Abstract:

[Objective] To investigate the diversity and potential value of the algae-associated symbiotic or epiphytic actinomycete resources from South China Sea, we isolated and identified actinomycetes from different algae samples collected from Xisha Islands and evaluated their antibacterial activities. [Methods] We used two types of media for the isolation and purification of actinomycetes and the isolates were identified according to their 16S rRNA gene sequences and the phylogenetic tree. The activities of their fermentation products against 10 pathogenic bacterial strains including Streptococcus agalactiae were tested with the punching method. The whole genome of the target active strain was sequenced and the biosynthetic gene clusters of secondary metabolites were predicted and analyzed by AntiSMASH. [Results] A total of 36 strains of actinomycetes were isolated from six kinds of algae. Based on 16S rRNA gene sequence and phylogeny analysis, they belonged to Streptomyces (2 strains), Rhodococcus (2 strains), Nocardia (3 strains), Micromonospora (5 strains), and Salinispora (24 strains), respectively. The antibacterial tests showed that the fermentation products of the 36 strains displayed inhibitory effect against at least one of ten sensitive bacteria. The antibacterial activities of Salinispora spp. were stronger than those of other actinomycetes. AntiSMASH analysis showed that more than 22.28% of the gene sequences in HZ014 genome were related to the biosynthesis of secondary metabolites, indicating their great potential in natural product biosynthesis. [Conclusion] The algae of Xisha Islands are home to abundant rare culturable actinomycetes. In this study, marine obligate rare actinomycetes associated with marine algae, Salinispora spp., were reported for the first time. The fermentation products of 36 strains of actinomycetes displayed antibacterial activity, indicating the potential value in the prevention of fish diseases. These rare actinomycetes are potential resources for the development of marine drugs or biocontrol agents.