A Plant Has Antibacterial Activity Polygala Rhizosphere Bacteria Identification And Their Metabolic Products Research

Plant rhizosphere Bacterial grow in the living tissues of plants, apparently without inflicting negative effects, These bacterial symbionts can have profound effects on plant ecology, fitness, and evolution, shaping plant communities and manifesting strong effects on the community structure and diversity of associated organisms. Many bacteria can make bioactive natural products that inhibit the growth of other organisms, and they are a potential source of novel products for use in medicine, agriculture, and industry. We isolated a bacterium of strong antagonistic activity from Polygala rhizospher.In this paper, both physiological characteristics and bioactive secondary products of the bacteria were studied.The taxonomic position of a novel bacterial strain, SNNU513, with antimicrobial a ctivity,isolated from the rhizosphere of Radix Polygalae in Yannan, Northwest China, was studied using a polyphasic approach.Cells of the strain were Gram-negative, rod-shaped, facultative anaerobes. It grew at a temperature of15～37℃(optimum30℃). Growth of the strain occurred between pH4.0and8.0, with an optimum of pH6.0-7.0.The strain inhibited mycelia growth of Pyricularia oryzae, Alternaria solani, Colletotrichum gloeosporioides, Rhizoctonia cerealis, Thanatephorus cucumeris Bacillus subtilis and E. coli.The G+C content of the total DNA was66.5mol%.The16SrDNA gene sequence of the strain was most closely related to species of the genus Lysobacter (97.0%to99.0%) sequence similarity.Chemotaxonomic data include major quinone, Q-8;Major polarlipids, Phosphatidyl ethanolamine, phosphatidyl glyeerol, phosphatidyl methylethanol amine and unknown structure containing glucosamine. Major fatty acids were iso-C15:0, iso-C16:0, iso-C17:1ω9c and iso-C11:03-OH were supported the affiliation of strain SNNU513to the genus Lysobacter. Phylogenetic analysis based on16S rDNA gene sequences, biochemical and physiological characteristics strongly supported the genotypic and phenotypic differentiation of strain SNNU513from species of Lysobacter with validly published names. Strain SNNU513therefore represents a novel species, for which the name Lysobacter yananisis is proposed.The antibacterial activity of this strain’s metabolites was further studied. The results showed that acetone extracts of the fermentation broth had a strong antibacterial activity, which can be inhibited by proteinase K and pepsin. Preparative SDS-PAGE was used for preliminary screening of the extracellular metabolites, and we found that the main active substances were small peptides and secondary metabolites. The discovery and identification of new strains can provide new resources for biomedical research and development in China. The active ingredients of their metabolites are expected to become the lead compounds of novel broad-spectrum antimicrobial agents.