Heindl Jason E, Hibbing Michael E, Xu Jing, Natarajan Ramya, Buechlein Aaron M, Fuqua Clay
Department of Biology, Indiana University, Bloomington, Indiana, USA.
Center for Genomics and Bioinformatics, Indiana University, Bloomington, Indiana, USA.
J Bacteriol. 2015 Dec 28;198(5):816-29. doi: 10.1128/JB.00668-15.
Transition metals such as iron and manganese are crucial trace nutrients for the growth of most bacteria, functioning as catalytic cofactors for many essential enzymes. Dedicated uptake and regulatory systems have evolved to ensure their acquisition for growth, while preventing toxicity. Transcriptomic analysis of the iron- and manganese-responsive regulons of Agrobacterium tumefaciens revealed that there are discrete regulatory networks that respond to changes in iron and manganese levels. Complementing earlier studies, the iron-responsive gene network is quite large and includes many aspects of iron-dependent metabolism and the iron-sparing response. In contrast, the manganese-responsive network is restricted to a limited number of genes, many of which can be linked to transport and utilization of the transition metal. Several of the target genes predicted to drive manganese uptake are required for growth under manganese-limited conditions, and an A. tumefaciens mutant with a manganese transport deficiency is attenuated for plant virulence. Iron and manganese limitation independently inhibit biofilm formation by A. tumefaciens, and several candidate genes that could impact biofilm formation were identified in each regulon. The biofilm-inhibitory effects of iron and manganese do not rely on recognized metal-responsive transcriptional regulators, suggesting alternate mechanisms influencing biofilm formation. However, under low-manganese conditions the dcpA operon is upregulated, encoding a system that controls levels of the cyclic di-GMP second messenger. Mutation of this regulatory pathway dampens the effect of manganese limitation.
Responses to changes in transition metal levels, such as those of manganese and iron, are important for normal metabolism and growth in bacteria. Our study used global gene expression profiling to understand the response of the plant pathogen Agrobacterium tumefaciens to changes of transition metal availability. Among the properties that are affected by both iron and manganese levels are those required for normal surface attachment and biofilm formation, but the requirement for each of these transition metals is mechanistically independent from the other.
铁和锰等过渡金属是大多数细菌生长所必需的微量营养素，作为许多关键酶的催化辅因子发挥作用。专门的摄取和调节系统已经进化出来，以确保获取这些金属用于生长，同时防止毒性。对根癌土壤杆菌铁和锰响应调节子的转录组分析表明，存在对铁和锰水平变化作出反应的离散调节网络。作为早期研究的补充，铁响应基因网络相当庞大，包括铁依赖性代谢和铁节约反应的许多方面。相比之下，锰响应网络限于有限数量的基因，其中许多基因可与过渡金属的转运和利用相关联。预测驱动锰摄取的几个靶基因在锰限制条件下的生长中是必需的，并且具有锰转运缺陷的根癌土壤杆菌突变体在植物致病性方面减弱。铁和锰限制独立抑制根癌土壤杆菌的生物膜形成，并且在每个调节子中鉴定出了几个可能影响生物膜形成的候选基因。铁和锰对生物膜的抑制作用不依赖于公认的金属响应转录调节因子，表明存在影响生物膜形成的替代机制。然而，在低锰条件下，dcpA操纵子上调，编码一个控制环二鸟苷酸第二信使水平的系统。该调节途径的突变减弱了锰限制的影响。
对过渡金属水平变化（如锰和铁的变化）的响应对于细菌的正常代谢和生长很重要。我们的研究使用全基因组表达谱来了解植物病原体根癌土壤杆菌对过渡金属可用性变化的响应。受铁和锰水平影响的特性包括正常表面附着和生物膜形成所需的特性，但每种过渡金属的需求在机制上相互独立。
