An Antimicrobial Substance Produced by Pseudomonas cepacia B5 against the Bacterial Wilt Disease Pathogen, Pseudomonas solanacearum

An antimicrobial substance produced by Pseudomonas cepacia B5 (B5) against the bacterial wilt disease pathogen, Pseudomonas solanacearum, was isolated and identified in order to clarify the mechanism for disease suppression by B5. A filtrate of the B5 culture showed high inhibitory activity against this pathogen. The active substance was isolated in pure form by chromatography with a Diaion HP20 column and by high-performance liquid chromatography with a Jaigel GS220 column. On the basis of IR, NMR, and mass spectra, the antimicrobial substance was identified as 2-keto-d-gluconic acid (2KGA). The production of 2KGA and the destruction of the disease pathogen in a contaminated soil suspension to which the B5 strain was added, together with wheat bran, suggested that 2KGA might be involved in disease suppression by P. cepacia B5.