Study on secondary metabolites of soil derived Streptomyces sp. CPCC 203679
Actinobacteria are an important resource for discovering new antibiotics, as they can produce a variety of active natural products with diverse structural types. Streptomyces is the dominant genus of actinomycetes, with the highest number of reported effective species. It is widely distributed in soil, freshwater, marine environments, and some organisms. Streptomyces is known for producing a wide variety of active secondary metabolites with diverse structural types, and is an important source of commonly used antibiotics in clinical practice. Currently, about two-thirds of the antibiotics used in clinical practice are produced by this genus of microorganisms. In recent years, a large number of structurally novel and biologically active secondary metabolites have been continuously reported from the genus Streptomyces, indicating that the discovery of new lead compounds from this genus still has great potential. Our research group discovered a strain of Streptomyces sp. CPCC 203679 derived from soil during the preliminary biological activity screening. The crude extract of its fermentation broth has good antibacterial activity. In this study, various modern chromatographic and spectroscopic techniques were used to preliminarily isolate, purify, and structurally identify the secondary metabolites of the strain, and 9 compounds were obtained (see Figure 1). Compounds 1-8 were evaluated for their in vitro antibacterial and cytotoxic activities.

 

Nine compounds were isolated from the fermentation broth of Streptomyces sp. CPCC 203679 derived from soil, including fatty acids, alkaloids, and cyclic dipeptides. Compound 1 is a new fatty acid compound, and compound 3 was isolated for the first time from soil derived Streptomyces. The pharmacological activity evaluation results showed that compounds 1-8 did not exhibit significant antibacterial and anti-tumor activity. Compound 2 belongs to the alkaloid class and is widely present in microorganisms such as actinomycetes, bacteria, and fungi, such as Streptomyces Bacillus、Aspergillus、Alternaria。 Compound 3 belongs to the indole alkaloid class and was first reported in 1965. This compound has also been reported in genera such as Bacillus, Balansia, Edwardsiella, etc. According to literature reports, compound 3 has anti pollution effects and has a certain inhibitory effect on the larvae of barnacles. Its ED50 is 18.6 μ mol/L. Cyclic dipeptides are the smallest cyclic peptides in nature, widely present in the metabolic products of plants, animals, and microorganisms, with activities such as antibacterial, anti-tumor, neuroprotective, and antithrombotic properties. This study did not isolate secondary metabolites with significant biological activity, which may be due to the fact that the biosynthetic gene clusters of active metabolites were not activated under current culture conditions, or were not isolated due to low production of active metabolites. In the future, we will attempt to optimize the cultivation conditions to increase the structural diversity of secondary metabolites, and further combine antibacterial activity evaluation to obtain structurally novel and significantly active secondary metabolites.