Isolation and characterization of Pseudomonas brassicacearum J12 as an antagonist against Ralstonia solanacearum and identification of its antimicrobial components

A bacterial strain, J12, isolated from the rhizosphere soil of tomato plants strongly inhibited the growth of phytopathogenic bacteria Ralstonia solanacearum. Strain J12 was identified as Pseudomonas brassicacearum based on its 16S rRNA gene sequence. J12 could produce 2,4-diacetylphloroglucinol (2,4-DAPG), hydrogen cyanide (HCN), siderophore(s) and protease. The maximum growth and antagonistic activity were recorded at 30 °C and pH 8. Glucose and tryptone were used as the most suitable carbon and nitrogen sources, respectively. Strain J12 significantly suppressed tomato bacteria wilt by 45.5% in the greenhouse experiment. The main antimicrobial compound of J12 was identified as 2,4-diacetylphloroglucinol (2,4-DAPG) by HPLC–ESI-MS analysis. The gene cluster phlACBD, which is responsible for 2,4-DAPG production, was identified and expressed in the bacterial strain Escherichia coli DH5α.