ABSTRACT
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.
ABSTRACT
BACKGROUND: Indole-3-acetic acid (IAA) is produced by microorganisms and plants via either tryptophan-dependent or tryptophan-independent pathways. Herein, we investigated the optimisation of IAA production by Streptomyces fradiae NKZ-259 and its formulation as a plant growth promoter to improve economic and agricultural development. RESULTS: The maximum IAA yield achieved using optimal conditions was 82.363 µg/mL in the presence of 2 g/L tryptophan after 6 days of incubation. Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) analysis of putative IAA revealed an RF value of 0.69 and a retention time of 11.842 min, comparable with the IAA standard. Regarding product formulation, kaolin-based powder achieved a suspension rate of 73.74% and a wetting time of 80 s. This carrier exhibited good shelf life stability for NKZ-259, and the cell population did not decrease obviously over 4 months of storage at 4 °C. In vivo analysis of plant growth promotion showed that tomato seedlings treated with kaolin powder containing NKZ-259 cells displayed a significant increase in root and shoot length of 7.97 cm and 32.77 cm, respectively, and an increase in fresh weight and dry weight of 6.72 g and 1.34 g. Compared to controls, plant growth parameters were increased almost it two-fold. CONCLUSION: Optimising the culture conditions resulted in an almost four-fold increase in IAA secretion by NKZ-259 cells. The results clearly demonstrate that S. fradiae NKZ-259 holds great potential for plant growth promotion and IAA production. Furthermore, kaolin-based powder is an effective carrier for NKZ-259 cells and may be useful for commercial applications.
