Chiang Mai Journal of Science

No previous studies have been carried out on the isolation and characterization of phosphate-solubilizing bacteria (PSB) in organic and conventionally grown chili (Capsicum frutescens L. cv. Hua Rua) in Ubon Ratchathani province, Thailand. This study aimed to isolate PSB from rhizophere soil of chili cultivated on organic and conventional farms. Characterization of organic acid and ability of mineral phosphate solubilization were also investigated. The effects of PSB on the growth of chili were observed in a pot trial. The most PSB (over 68%) could be obtained from organically managed soil. Ten isolates of PSB were selected based on tricalcium phosphate solubilizing ability, and further testing was carried out for characterization of organic acids. The selected PSB exhibited phosphate-solubilizing ability ranging between 126.36-488.55 mg/ml of phosphate. Additionally, the 16s rRNA gene and phylogenetic analysis showed maximum similarity to Burkholderia ambifaria and B. tropica. HPLC analysis of organic acids produced from these isolates in a culture medium found eight different kinds of organic acids: acetic acid, citric acid, gluconic acid, lactic acid, succinic acid, propionic acid, and two unknown organic acids. Among, the isolates in this study, multiple organic acids could be produced from eight isolates, and a single acid was found from two isolates. Multiple organic acids did not correspond with an ability to solubilize mineral phosphate. Isolate KS04 was obtained from a conventional chili farm, and showed the greatest efficiency in promotion of chili growth cultivated in sterile organically managed soil; it significantly increased the growth, flowering and Puptake, compared to uninoculated plants. Thus, this isolated may be useful for use as a bio-inoculant for chili production in organically managed soil.