Diversity of actinobacteria from mangrove sediment in Gaoqiao, Zhanjiang and identification of germicidins from one strain of Streptomyces

Abstract:

[Objective]The present work aims to isolate and identify actinobacteria from rhizosphere sediments of 3 mangrove plants and to investigate the target strain for secondary metabolites based on antibacterial activities. [Methods] Five media were used to isolate actinobacteria from rhizosphere sediments of mangrove plants in Gaoqiao, Zhanjiang. The isolates were identified based on 16S rRNA genes and then screened for antibacterial activities against 6 indicator strains. The target strain was selected for upscaled fermentation and identification of bioactive compounds. We then analyzed the biosynthetic gene cluster of the isolated compounds to predict the biosynthetic pathways. [Results]A total of 49 actinobacterial strains were isolated and categorized into 6 genera including Streptomyces (31 strains), Micromonospora (14 strains), Microbispora (1 strain), Streptosporangium (1 strain), Nonomuraea (1 strain), and Saccharomonospora (1 strain). Six α-pyrones, including germicidins A–C, germicidin I, and isogermicidins A–B, were separated from the crude extract of Streptomyces sp. SCSIO 40067 and identified. The crystal structure of germicidin A was reported for the first time. The type Ⅲ polyketide synthase biosynthetic gene cluster of α-pyrones was localized in the SCSIO 40067 genome by bioinformatics analysis. The biosynthetic pathway of α-pyrones was then proposed. [Conclusion]Actinobacteria in the rhizosphere sediment of mangrove plants in Gaoqiao, Zhanjiang had high species diversity, from which new species capable of producing valuable natural products can be mined.Streptomyces sp. SCSIO 40067 can produce α-pyrones via the type Ⅲ polyketide synthase pathway, which can serve as a start strain for the following studies.