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Pathogenic bacteria are the primary causative agents of economic losses in the aquaculture industry, and biological control is currently regarded as a promising strategy for prevention and management. Algae, as crucial components of marine ecosystems, host diverse and abundant microbial communities within their phycospheres. In order to explore the diversity and potential application value of algae-associated symbiotic or epiphytic actinomycetes resources in South China Sea, the isolation identification and antibacterial activity screening of symbiotic or epiphytic actinomycetes from Caulerpa sertularoides f. Longipes, collected from Lingshui, Hainan, were carried out. Actinomycetes were isolated through dilution coating method and identified according to the 16S rRNA gene sequences alignment and by phylogenetic tree construction. The results revealed that 20 strains were identified as Streptomyces, one as Nocardiopsis, and one as Microbacterium. The antibacterial activity of the fermented crude extracts of the obtained strains was evaluated against nine pathogenic bacteria, including Vibrio owensii using the filter paper method. Results showed that all strains exhibited inhibitory effects on at least one type of bacteria. High-performance liquid chromatography (HPLC) was employed to assess the chemical diversity of the crude extracts. Results showed that strain HZ057 had a higher abundance of secondary metabolites than other strains. To further investigate the salt stress tolerance of the strains, salt tolerance tests were conducted. The results showed that all the strains could grow well on 0%-4% NaCl, HZ054 and HZ057 could still grow at a salt concentration of 12%. The whole genome of HZ057 was sequenced and the functions of each gene cluster were predicted using antiSMASH. The analysis revealed that the genome contained 29 secondary metabolite genes clusters with diverse structural types, indicating that this strain is associated with a rich diversity of secondary metabolites. In this study, strains of Streptomyces, Nocardiopsis and Micrococcus were isolated firstly from the algae Caulerpa sertularoides f. Longipes in the South China Sea, indicating that the algae contained abundant actinomycete resources. Moreover, it was found that the identified strains exhibited significant antibacterial activity and the ability to produce a variety of secondary metabolites, suggesting the potentials for future research and applications.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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