Isolation and identification of endophytic actinomycetes from the seeds of Camptotheca acuminata Decne. and isolation of antimicrobial substances from those endophytic actinomycetes

Abstract:

[Objective] The seeds of Camptotheca acuminata Decne. containing camptothecin (an anticancer agent), was investigated to explore the endophytic actinomycetes diversity and screen for new active compounds producing strain. [Methods] The seeds of C. acuminata Decne. were sliced and plated on different selective media after surface sterilization. Colonies that looked like actinomycetes were selected, and identified according to the colonial morphology and 16S rRNA sequence analysis. Strains isolated were tested for antimicrobial activity using co-culture method. [Results] Thirty-three suspected endophytic actinomycetes strains were isolated from the C. acuminata Decne. seeds collected in campus of Shanghai Jiao Tong University. Among the suspected endophytic actinomycetes isolated, twenty-one were identified as Streptomyces, one was Nocardiopsis by 16S rRNA sequence analysis. Three endophytes were left to be determined due to low sequence similarity (less than 95%). The other eight strains were failed to be identified because of failure of their 16S rRNA sequence cloning. Further study was needed to determine whether or not these eleven strains were new actinomycetes species. Preliminary antibacterial and antifungal activity survey of strains isolated showed that approximately 42.42% of them can strongly inhibit the sclerotia formation of Rhizoctonia solani Kühn, and 54.54% of them can strongly inhibit the growth of Bacillus subtilis. Further, the metabolites of one representative strain—Streptomyces sp. CXSZ1 was studied and found to contain antibacterial compounds. [Conclusion] Study of isolation and identification of endophytic actinomycetes from the C. acuminata Decne. seeds and isolation of antimicrobial substances from the endophytic actinomycetes not only revealed the origination and evolution of endophytes in C. acuminata Decne. seeds, but also provided unique material for mining new structural and new bio-active compounds.