Isolation and antibacterial activity of Xisha stone coral-associated actinomycetes

Abstract:

[Background] Coral reef ecosystem is extremely important in the marine ecosystem, in which the actinomycetes are the important line of defense against various pathogens. Therefore, coral-associated actinomycetes are important resources for molecules with antibacterial activity, indicating tremendous medicinal potential.[Objective] To isolate the culturable actinomycetes from samples of Xisha stone corals and screen out the strains with good antibacterial activity. [Methods] Coral-associated actinomycetes were isolated by dilution separation method and identified by phylogenetic analysis of 16S rRNA gene sequence. The antibacterial activity test was conducted by the plate confrontation method, and the target strain was identified. The salinity tolerance test was carried out by plating the strain on ISP2 solid medium with different concentrations of NaCl, and the thermostability and photostability of the fermentation products were tested by the plate confrontation method. The genome of the target active actinomycete was sequenced by Nanopore and Illumina sequencing, and the types of biosynthetic gene clusters of secondary metabolites were analyzed online by antiSMASH. [Results] A total of 104 culturable actinomycetes were isolated from 6 samples of Xisha stone corals, and 27 actinomycetes were obtained after removing duplicates according to colony morphology and sample source. The 16S rRNA gene sequencing of the 27 strains was performed, and they were identified as Salinispora (25 strains), Streptomyces (1 strain), and Gordonia (1 strain) according to sequence alignment and phylogenetic tree analysis. The results of activity screening showed that Salinispora sp. SH098 had the optimal antibacterial activity during the antibacterial activity test. Salinispora sp. SH098 did not grow in the salt-free medium and its salt-tolerant range was 2%-5%. Its fermentation products showed good thermostability and photostability. The whole genome sequence analysis showed that 21.93% of the gene sequences of strain SH098 were related to the biosynthesis of secondary metabolites. The structure types of predicted metabolites were diverse, which needed to be further explored. [Conclusion] This is the first report on Salinispora spp. with anti-agricultural pathogenic bacteria activity from Xisha stone corals in China, which enriches the obligate marine actinomycetes resources from the Xisha islands of China. It provides new resources for the development of new microecological agents applied to mariculture and also lays a foundation for mining antibacterial active substances.