Abstract：
The soil-borne phytopathogenic gram-negative bacterium Ralstonia solanacearum species complex (RSSC) produces staphyloferrin B and micacocidin as siderophores that scavenge for trivalent iron (Fe3+) in the environment, depending on the intracellular divalent iron (Fe2+) concentration. The staphyloferrin B-deficient mutant reportedly retains its virulence, but the relationship between micacocidin and virulence remains unconfirmed. To elucidate the effect of micacocidin on RSSC virulence, we generated the micacocidin productivity-deficient mutant (ΔRSc1806) that lacks RSc1806, which encodes a putative polyketide synthase/non-ribosomal peptide synthetase, using the RSSC phylotype I Ralstonia pseudosolanacearum strain OE1-1. When incubated in the condition without Fe2+, ΔRSc1806 showed significantly lower Fe3+-scavenging activity, compared with OE1-1. Until 8 days after inoculation on tomato plants, ΔRSc1806 was not virulent, similar to the mutant (ΔphcA) missing phcA, which encodes the LysR-type transcriptional regulator PhcA that regulates the expression of the genes responsible for quorum sensing (QS)-dependent phenotypes including virulence. The transcriptome analysis revealed that RSc1806 deletion significantly altered the expression of more than 80% of the PhcA-regulated genes in the mutant grown in medium with or without Fe2+. Among the PhcA-regulated genes, the transcript levels of the genes whose expression was affected by the deletion of RSc1806 were strongly and positively correlated between the ΔRSc1806 and the phcA-deletion mutant. Furthermore, the deletion of RSc1806 significantly modified QS-dependent phenotypes, similar to the effects of the deletion of phcA. Collectively, our findings suggest that the deletion of micacocidin production-related RSc1806 alters the regulation of PhcA-regulated genes responsible for QS-dependent phenotypes including virulence as well as Fe3+-scavenging activity. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
摘要：
土壤传播的植物病原性革兰氏阴性细菌青枯病菌（RSSC）产生葡萄球菌铁蛋白B和杀微生物素作为铁载体，可清除环境中的三价铁（Fe3），取决于细胞内二价铁（Fe2+）浓度。据报道，葡萄球菌B缺陷突变体保留了其毒力，但是杀微生物素与毒力之间的关系仍未得到证实。为了阐明杀微生物素对RSSC毒力的影响，我们产生了缺乏RSc1806的micacocidin生产力缺陷型突变体（ΔRSc1806），该突变体编码推定的聚酮合成酶/非核糖体肽合成酶，使用RSSC基因型I假青枯菌菌株OE1-1。当在无Fe2+的条件下孵育时，ΔRSc1806显示出明显较低的Fe3清除活性，与OE1-1相比。直到接种番茄植物后8天，ΔRSc1806没有毒力，类似于突变体(ΔphcA)缺失phcA，其编码LysR型转录调节因子PhcA,其调节负责群体感应(QS)依赖性表型(包括毒力)的基因的表达。转录组分析显示，RSc1806缺失显着改变了在含或不含Fe2的培养基中生长的突变体中超过80％的PhcA调节基因的表达。在PhcA调节的基因中，在ΔRSc1806和phcA缺失突变体之间，其表达受RSc1806缺失影响的基因的转录水平强且正相关。此外，RSc1806的缺失显著修饰了QS依赖性表型，与phcA缺失的效果相似。总的来说，我们的发现表明，与micacocidin产生相关的RSc1806的缺失改变了对负责QS依赖性表型的PhcA调节基因的调节，包括毒力以及Fe3清除活性。[公式：见正文]版权所有©2024作者（S）。这是在CCBY-NC-ND4.0国际许可证下分发的开放访问文章。
