Isolation, Screening and Preliminary Identification of Endophytic Actinobacteria from Mangroves at Shankou of Guangxi Province

Abstract:

Fourty one plant tissue samples, including root, stem, leaf and hypocotyl were collected from 8 kinds of eumangrove and 5 kinds of semi-mangrove at Shankou Mangrove Nature Reserve in Guangxi Province. These samples were grinded into little pieces after surface sterilization, and then seeded into the isolation media containing chitin, humic acid or xylan as the main nutrition and energy source. As a result, 118 actinobacterial strains were purified from these plant tissue samples. These isolates were screened using 6 models for screening new antibiotics, and the fermentation broths from 77 strains exhibited activity on at least one screening model, the positive rate among the isolates is 65.3%. Based on the morphological characteristics, chemotaxonomic and 16S rRNA gene analysis, 77 isolates were identified as Streptomyces spp. (44), Micromonospora spp. (25), Saccharothrix spp. (3), Nocardia spp. (3), Nocardiopsis sp. (1) and Lentzea sp. (1). Strain I07A-01824, which showed strong antibacterial activity against the test strain Enterococcus faecalis HH22 (a multi-resistant clinical isolate) and positive activity on the screening model of statins-like antihyperlipidemics, was identified as a member of a known species Streptomyces albidoflavus. This study demonstrates that an unexpected diversity of actinobacteria colonizes inside the mangrove tissues, and these endophytic actinobacteria are promising sources of new natural secondary metabolites with physiological activities.