Species diversity and anti-biofilm components of rhizosphere microorganisms derived from Astragalus forrestii in special high-cold environments

Abstract:

There are abundant plant resources of Astragalus in the high-cold region of northwestern Yunnan. These plants have obvious rhizosphere effect and their rhizosphere microorganisms are considered medicinal resources with great antimicrobial potential. [Objective] To understand the species diversity of rhizosphere microorganisms of Astragalusforrestii growing in the special high-cold environment of northwestern Yunnan, and the chemical diversity and the antimicrobial and anti-biofilm activities of the secondary metabolites produced by cultivable strains. [Methods] Metagenomic sequencing and culture-dependent method were employed to explore the microbial diversity in the rhizosphere soil of A. forrestii. High performance liquid chromatography (HPLC) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) were combined with broth microdilution and microplate assays to evaluate the chemical diversity and antimicrobial and anti-biofilm activities of the ethyl acetate (EA) extracts of strain fermentation broths. [Results] The operational taxonomic units of the rhizosphere soil samples of A. forrestii were classified and annotated to 856 species belonging to 316 genera, 187 families, 105 orders, 54 classes, and 22 phyla. Bradyrhizobium was the dominant genus. A total of 95 cultivable strains of 54 species belonging to 27 genera were obtained, including 54 bacterial strains of 33 species belonging to 20 genera and 41 fungal strains of 21 species belonging to 7 genera, among which Bacillus and Penicillium were predominant. The secondary metabolites of the bacterial strain Pseudomonas tolaasii ZTB4 and the fungal strains Aspergillus tabacinus ZNF17, Lecanicillium aphanocladii ZNF15, and Umbelopsis nana ZTF31 displayed broad-spectrum antimicrobial activities. The secondary metabolites of strains ZTB4 and ZNF17 showed strong inhibitory activity against the biofilm formation of methicillin-resistantStaphylococcus aureus (MRSA). The main active components of these two strains were cyclic lipopeptides and flavonoids, respectively. [Conclusion] The rhizosphere soil of A. forrestii harbors rich microorganism, and the secondary metabolites of some cultivable strains have high chemical diversity and strong antimicrobial and anti-biofilm activities. The results provide a theoretical basis for the development and utilization of characteristic microbial medicinal resources in special environments in China.