Characterization of bacterial endophytes from Myanmar medicinal plants for antimicrobial activity against human and plant pathogens

This research aimed to investigate the antagonistic activity of the bacterial endophytes from Myanmar medicinal plants. Thirty-one bacterial isolates were isolated from Myanmar medicinal plants: Tinospora cordifolia (Wild.) Miers., Catharanthus roseus G. Don., Tectona hamiltoniana Wall. and Boscia variabilis Collett & Hemsl. (Capparaceae). Dual culture and agar well diffusion methods were used for antimicrobial assay. One endophyte from Catharanthus roseus and two bacterial isolates from Boscia variabilis Collett & Hemsl. (Capparaceae) had not only the antibacterial activity towards the human pathogenic bacteria but also the antifungal activity against the plant pathogenic fungi. From 16S rRNA sequencing, one strain from Catharanthus roseus G. Don. was Bacillus amyloliquefaciens DSM7 and two antagonistic strains from Boscia variabilis Collett & Hemsl. (Capparaceae) were Bacillus subtilis subsp. subtilis str. 168 and Bacillus amyloliquefaciens DSM7, respectively. The best medium for the maximum production of the bioactive compounds was Bacillus medium supplemented with the 4% of starch and 0.3% of peptone for B. amyloliquefaciens DSM7 and B. subtilis subsp. subtilis str. 168 showed the maximum antimicrobial compounds production when it was incubated in the medium amended with 3% of starch and 2% of peptone. The optimum conditions for the the maximum production of the antimicrobial compound were the medium pH of 6 at 35 ºC after two days of incubation for B. amyloliquefaciens DSM 7 and B. subtitlis subsp. subtilis str. 168 secreted the maximum concentration of the bioactive compounds at pH 7.5 and 35˚C on second day incubation period. In conclusion, the isolated endophytic bacteria showed the strong antimicrobial activity towards the pathogenic microbes and they could be used in medicine and agriculture as well.本研究旨在探究缅甸药用植物内生细菌的拮抗活性。研究人员从缅甸药用植物青牛胆（Tinospora cordifolia (Wild.) Miers.）、长春花（Catharanthus roseus G. Don.）、滇柚木（Tectona hamiltoniana Wall.）以及变叶节蒴木（Boscia variabilis Collett & Hemsl.，山柑科）中分离得到31株细菌分离物。本研究采用双培养法与琼脂孔扩散法开展抗菌活性检测。其中，取自长春花的1株内生细菌以及取自变叶节蒴木的2株细菌分离物，不仅对人类致病细菌具有抗菌活性，同时可抑制植物致病真菌的生长。经16S rRNA测序鉴定，取自长春花的1株菌株为解淀粉芽孢杆菌（Bacillus amyloliquefaciens）DSM7；取自变叶节蒴木的2株拮抗菌株分别为枯草芽孢杆菌枯草亚种（Bacillus subtilis subsp. subtilis）str. 168与解淀粉芽孢杆菌DSM7。对于解淀粉芽孢杆菌DSM7，可使其生物活性物质产量达到峰值的培养基为添加4%淀粉与0.3%蛋白胨的芽孢杆菌培养基；而枯草芽孢杆菌枯草亚种str. 168在添加3%淀粉与2%蛋白胨的培养基中培养时，抗菌物质产量最高。解淀粉芽孢杆菌DSM7合成抗菌物质的最优条件为：培养基pH值6.0、培养温度35℃、培养时长2天；枯草芽孢杆菌枯草亚种str. 168则在pH7.5、35℃条件下培养2天，可分泌浓度最高的生物活性物质。综上，本研究分离得到的内生细菌对病原微生物展现出强劲的抗菌活性，可应用于医药与农业领域。