Ralstonia solanacearum is a soil-borne pathogen that causes bacterial wilt in plants. The wild-type strain of R. solanacearum undergoes spontaneous phenotype conversion (PC), from a fluidal to non-fluidal colony morphology. PC mutants are non-pathogenic due to reduced virulence factors, and can control wilt diseases as biological control agents. The induction factors of PC in R. solanacearum are currently unclear. Here, we investigated the effect of iron treatment on bacterial growth of wild-type strain and PC mutant, and PC of the wild-type strain in liquid medium. Interestingly, PC was frequently induced in the single cultured wild-type strain by iron treatment; however, PC was not induced in the co-culture. In a co-culture of both strains, the PC mutant showed increased growth compared to the wild-type strain by iron treatment. Furthermore, we investigated the effects of iron treatment on the bacterial growth and PC of the wild-type strain under different culture conditions of medium type (MM broth, BG broth, and water medium), iron compounds, and pH. In BG broth, PC occurred frequently regardless of iron treatment. In MM broth, the optimal conditions for high frequency induction of PC by iron treatments were treatment of iron (III) EDTA, and under pH 7–8. Conversely, PC was not induced by iron treatment in water medium and in MM broth under pH 5 conditions. Common to the culture conditions wherein PC was not induced by iron treatment, the bacterial density of the wild-type strain was as low as 10⁶ CFU mL⁻¹ or less. Finally, we investigated the effects on bacterial growth and PC of the wild-type strain by the iron treatment and addition of culture filtrate after cultivation of the wild-type strain at high concentration. In medium containing only the culture filtrate, PC did not occur. However, in medium containing the culture filtrate and iron, PC occurred frequently. Our results thus suggest that high-density growth of the wild-type strain as well as the presence of iron are involved in inducing PC in R. solanacearum.

青枯病菌是一种土壤传播的病原体，可导致植物青枯病。R. solanacearum的野生型菌株经历自发表型转换 (PC)，从流体菌落到非流体菌落形态。由于毒力因子减少，PC 突变体是非致病性的，并且可以作为生物防治剂控制枯萎病。青枯菌中PC的诱导因子目前还不清楚。在这里，我们研究了铁处理对野生型菌株和 PC 突变体的细菌生长的影响，以及液体培养基中野生型菌株的 PC。有趣的是，在单一培养的野生型菌株中，铁处理经常诱导 PC；然而，共培养中未诱导 PC。在两种菌株的共培养中，通过铁处理，PC 突变体与野生型菌株相比显示出增加的生长。此外，我们研究了在培养基类型（MM 肉汤、BG 肉汤和水培养基）、铁化合物和 pH 值的不同培养条件下，铁处理对野生型菌株的细菌生长和 PC 的影响。在 BG 肉汤中，无论铁处理如何，PC 都经常发生。在MM肉汤里，通过铁处理高频诱导 PC 的最佳条件是铁 (III) EDTA 处理和 pH 7-8。相反，在 pH 5 条件下，在水介质和 MM 肉汤中进行铁处理不会诱导 PC。与未通过铁处理诱导 PC 的培养条件相同，野生型菌株的细菌密度低至 10⁶  CFU mL ^-1或更少。最后，我们研究了铁处理和在高浓度培养野生型菌株后添加培养滤液对野生型菌株的细菌生长和 PC 的影响。在仅含有培养滤液的培养基中，没有发生 PC。然而，在含有培养滤液和铁的培养基中，PC 经常发生。因此，我们的结果表明，野生型菌株的高密度生长以及铁的存在参与了青枯菌的 PC 诱导。