Identification and antibacterial activity study of an antagonistic endophytic bacterium HJ-3 in Polygonatum sibiricum
Endophytes are a type of organism that inhabits healthy plant tissues and establishes a harmonious symbiotic relationship with the plant host over a long period of evolution. Research has found that endophytic bacteria in plants have great potential for application in biological control of plant diseases. There are also studies indicating that endophytic bacteria in plants can produce metabolites that are the same or similar to those of the host, especially some metabolites produced by medicinal endophytic bacteria that have good therapeutic effects on human diseases. They have been reported as therapeutic agents for diseases such as cancer, tumors, and bacterial and fungal infections. For example, Bos et al. reported that endophytic extracts isolated from the traditional Canadian medicinal plant Heraclium maximum have anti mycobacterial activity and can be studied as anti-cancer natural products; Seo et al. found that endophytic bacteria in radish have antibacterial activity against pathogens and can be used as biological control agents against human and plant pathogens, among others.

Polygonatum cyrtonema, a plant of the Liliaceae family, is mainly composed of steroidal saponins and Polygonatum polysaccharides. It has important pharmacological effects in enhancing immunity, anti-tumor, hypoglycemic, and antibacterial properties. As a medicinal and edible plant, it has been widely used in the fields of medicine, food, cosmetics, etc. However, most products are still in the initial processing stage, and further research is needed on the active ingredients of Polygonatum sibiricum to develop more deeply processed Polygonatum sibiricum products. There are few reports on endophytic fungi of Polygonatum sibiricum, for example, Li isolated endophytic fungi with antibacterial activity from Polygonatum sibiricum of Mount Taishan; Wang isolated endophytic fungi from Zhejiang Polygonatum sibiricum and studied their antibacterial metabolites. And endophytic bacteria in plants vary in their host plant regions, growth stages, tissue locations, and types. Bai, Zhai, and others screened endophytic strains of Bacillus subtilis and Bacillus subtilis from Anhui Polygonatum sibiricum and conducted antibacterial activity studies. In this study, another endophytic strain HJ-3 with antagonistic effects was isolated from Polygonatum sibiricum in Anhui Province. It was classified, identified, studied for activity, and analyzed for metabolites, in order to lay the foundation for enriching the endophytic bacterial resources of Polygonatum sibiricum and its development and utilization.

Endophytic bacteria produce many bioactive substances with medicinal value during symbiosis with their hosts, which have potential value in the prevention and control of human diseases such as cancer, antibacterial, and antioxidant, as well as in the field of agricultural pest control. There are many research reports on endophytic bacteria both domestically and internationally. For example, Halim et al. isolated two endophytic bacteria, BCA3 and BCA12, from the roots and leaves of rice paddies, and found that they have positive antagonistic activity against bacterial leaf blight (BLB); Botrytis cinerea is one of the most important post harvest fungal pathogens. Chao et al. screened endophytic bacteria from different plants and found that it has biocontrol effects on Botrytis cinerea in tomatoes; The study on endophytic fungus HJ-3 obtained in this project found that it has antagonistic effects on plant pathogenic fungi and exhibits broad-spectrum antagonistic activity. Zhang et al. isolated a broad-spectrum antagonistic bacterium XS-2 from wheat spikelets and found that it has inhibitory effects on six plant pathogens, including Fusarium graminearum, the pathogen of Fusarium head blight (FHB), and Fusarium oxysporum, the pathogen of cotton. The inhibition zone is between 10-29.58mm, making it a valuable biological resource for developing biocontrol agents. The endophytic bacterium HJ-3 obtained in this study has the same inhibitory effect on plant pathogenic fungi such as Fusarium graminearum and Fusarium graminearum. The difference is that the endophytic bacterium was not isolated from crops, but from the medicinal plant Polygonatum sibiricum. Scientists have shown that isolating endophytic bacteria from plants, especially some medicinal plants, can inhibit the growth of pathogenic bacteria and fungi. This may be due to the production of metabolites during the symbiotic process between endophytic bacteria and medicinal plants, which have inhibitory effects on pests, diseases, or pathogens. Bai et al. isolated endophytic strains HJ-1 and HJ-2 from the medicinal plant Polygonatum sibiricum, and found that their fermentation products had good inhibitory effects on pathogenic bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus. In this study, endophytic strain HJ-3 was isolated from the medicinal plant Polygonatum sibiricum, which also showed widespread antibacterial effects on common pathogenic bacteria. However, this study focused on exploring the antagonistic effect of endophytic bacteria on plant pathogenic fungi, thereby enriching the potential application value of endophytic bacteria in Polygonatum sibiricum. Existing data indicates that screening endophytic bacteria from medicinal plants for the production of bioactive compounds with medicinal value, especially from endophytic bacteria of endangered host plants, has become an important source of bioactive compounds for the development of new drugs.

The project is to screen an endophytic strain HJ-3 from the authentic Anhui medicinal herb Polygonatum sibiricum. After preliminary morphological identification and 16S rRNA molecular biology sequencing, the strain was identified as Bacillus velezensis. Bacillus thuringiensis is widely used in the fields of industry, agriculture, and environmental protection due to its broad-spectrum antibacterial activity, promoting plant growth, and potential as a biosurfactant. It can also be used as a feed microbial agent and is expected to play a more important role in healthcare. But different strains of the same species B Velezensis has functional differences, so further exploration of B. in nature is needed Develop and utilize new functional strains of velezensis strain resources. Chi et al. also isolated Bacillus velezensis strain ZJKU-3 from Polygonatum multiflorum and studied the antagonistic activity of endophytic bacteria and their metabolites against Fusarium oxysporum. The B. separated in this study The velezensis strain HJ-3 has inhibitory effects on plant pathogenic fungi, including Fusarium oxysporum, Fusarium oxysporum, Fusarium oxysporum, Fusarium graminearum, Fusarium oxysporum, Fusarium graminearum, and Fusarium oxysporum, in addition to Fusarium oxysporum. It particularly has a very significant inhibitory effect on Fusarium oxysporum, followed by Fusarium oxysporum, Fusarium oxysporum, Fusarium oxysporum, Fusarium oxysporum, and Fusarium oxysporum. It can be seen that the endophytic bacterium HJ-3 obtained in this study has broad-spectrum antagonistic activity against common plant pathogenic fungi, and its research results have certain guiding significance for the biological control of agricultural pests and diseases. In addition, research has found that the fermentation products of endophytic strain HJ-3 exhibit extensive antibacterial effects on common bacteria, especially on Staphylococcus aureus, which has the most significant antibacterial effect. Staphylococcus aureus is a common clinical pathogen and its antibiotic resistance is very common. Therefore, finding effective antibacterial drugs, especially new types of antibacterial drugs from natural products, is of great significance for the prevention and treatment of bacterial diseases, and is also one of the methods to solve the problem of bacterial resistance.

The above research shows that the HJ-3 endophytic strain selected from the traditional Chinese medicine Huangjing has a significant antagonistic effect on various plant pathogenic fungi, and its fermentation products can inhibit the growth of common bacteria such as Escherichia coli. Through UPLC-MS/MS, 5,5 ‘- methylenebis (2-tert-butyl-4-methylphenol) phenolic compounds were detected from the fermentation products of endophytic bacteria, and three compounds of the same series were obtained. The data obtained in this study will lay the foundation for further exploring the active ingredients in the fermentation products of Polygonatum sibiricum endophytes, and provide a basis for the widespread application of plant endophytic drugs.