2026 Volume 64 Issue 2 Pages 59-66
Ralstonia pseudosolanacearum is a soilborne bacterium causing bacterial wilt. The wild-type strain undergoes phenotypic conversion (PC) to its avirulent form, and PC mutants function as biocontrols for plant diseases. However, the underlying mechanisms of PC is unclear. In this study, we investigated the effect on induction of PC in wild-type strains by addition of iron chloride (IC), citric acid (CA) and ferric ammonium citrate (FAC) in minimal medium (MM) broth. PC frequently occurred in MM broth supplemented with IC or CA, alone or in combination, under static culture conditions. However, PC was not induced by shaking culture. We investigated PC induction in five strains (phylotype I) of different classifications. Strains 8238, 8216, and 8232 were likely to induce PC by adding 1% CA and 0.1–1% FAC; however, 8214 and 8357 strains were less likely to undergo PC. The frequency of PC by FAC varied depending on the bacterial strain and pH 5–8 conditions; strains 8238 and 8216 frequently induced PC, but strain 8214 did not induce PC. This study clarified the culture conditions and bacterial strains likely to induce PC by application of IC, CA, and FAC, and will be useful for elucidating the mechanism of PC.
