Mechanism of plant growth promotion elicited by Bacillus sp LKE15 in oriental melon

摘要

Development of organic fertilizers using microbial extracts is an emerging method in organic farming. The objective of this study was to identify and characterize the bioactive substances in a plant growth-promoting bacterial culture, intended to enhance the growth of oriental melons (Cucumis melo L.). LKE15 was isolated from oriental melon rhizosphere soil and identified as Bacillus sp. LKE15 through 16S rDNA sequencing of the bacterial genomic DNA and a subsequent phylogenetic analysis. Bacillus sp. LKE15 was found to enhance the shoot length, fresh weight, dry weight, and chlorophyll content of both dwarf rice (gibberellins [GAs]-deficient mutant, waito-C) and normal rice (active GAs biosynthesis, Hwayoungbyeo) cultivars, as compared to their controls. The presence of bioactive metabolites such as GAs (GA(4), GA(9), and GA(34)), indole-3-acetic acid, and high concentrations of phosphate in the bacterial culture filtrate (CF) significantly promote host plant growth. The plant growth-stimulating effect of CF was confirmed by the increased shoot length, root length, and plant fresh weight of oriental melon as compared to the controls. Similarly, Bacillus sp. LKE15 inoculation also enhanced plant growth but at a lower rate than CF. The increased synthesis of chlorophyll and individual amino acids and their derivatives, including taurine, aspartic acid, threonine, serine, glycine, alanine, citrulline, isoleucine, leucine, tyrosine, beta-alanine, gamma-amino-n-butyric acid, ethanolamine, 1-methylhistidine, and hydroxyproline in CF-treated plants reflected a significant increase in the growth of treated plants, as compared to the control. However, magnesium, potassium, and phosphorus contents were significantly enhanced in plants treated with CF. Results of this study suggest that the availability of bioactive metabolites in the CF of Bacillus sp. LKE15 stimulates plant growth, and that treatment with the CF of Bacillus sp. LKE15 would be a useful tool for the organic farming of crop plants.