Diversity and antibacterial activity of endophytic bacteria in Rheum tanguticum

Abstract:

[Background] The overuse and misuse of antibiotics accelerate the emergence of drug-resistant bacteria and pose a threat to global health and development. Therefore, it is urgent to develop new antibiotics. Rheum tanguticum, a Chinese medicinal herb, contains a variety of active ingredients and has antimicrobial, antiviral, hemostatic, cholagogic, and antitumor effects. Endophytes of medicinal plants can produce the same or similar metabolites in the long-term evolution with their hosts, becoming an important source for the development of new drugs. [Objective] To explore the diversity of endophytic bacteria in R. tanguticum and screen out the bacteria with antibacterial activity, thus providing microbial resources for the development of natural antibacterial drugs. [Methods] The endophytic bacteria were isolated by dilution coating on three culture media and identified by 16S rRNA gene sequencing. The agar block method was used to screen the endophytic bacteria with antibacterial activity. The antibacterial activities and whole genome sequences of the strains screened out were determined. [Results] A total of 100 strains of endophytic bacteria were isolated from R. tanguticum, belonging to 43 genera, 26 families, 17 orders, 8 classes of 4 phyla, of which Firmicutes was the dominant phylum (35%) and Bacillus (9%) was the dominant genus. The preliminary screening results showed that 13 strains exerted inhibitory effects on different pathogens, and one of them, RTM5-22, had strong inhibitory effects on 5 pathogenic bacteria. The crude n-butanol extract of the fermentation broth of RTM5-22 showed inhibitory activities against 7 pathogens. The genome of RTM5-22 contained the gene clusters for synthesizing secondary metabolites such as polyketones and terpenes, ribosomes, and post-translational modified peptides. [Conclusion] There are rich endophytic bacteria in R. tanguticum. We isolated a number of strains with excellent antibacterial activities, which provides data support for the follow-up study of endophytic bacteria from R. tanguticum. The metabolites of RTM5-22 have broad-spectrum antibacterial activities, which can provide resources for mining new and efficient natural antibacterial substances.

Key words:Rheum tanguticum;endophytic bacteria;diversity;whole genome sequencing;antimicrobial activity