Rondon Michelle R, Ballering Katie S, Thomas Michael G
Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Room 256 Biochemistry, 420 Henry Mall and Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Microbiology (Reading). 2004 Nov;150(Pt 11):3857-3866. doi: 10.1099/mic.0.27319-0.
Using the complete genome sequence from Agrobacterium tumefaciens C58, the authors identified a secondary metabolite gene cluster that encodes the biosynthesis of a metabolite with siderophore activity. Support for this conclusion came from genetic and regulatory analysis of the gene cluster, along with the purification of a metabolite from A. tumefaciens C58 with iron-chelating activity. Genetic analysis of mutant strains disrupted in this gene cluster showed that these strains grew more slowly than the wild-type strain in medium lacking iron. Additionally, the mutant strains failed to produce a chrome-azurol-S-reactive material in liquid or solid medium, and failed to produce the metabolite with iron-chelating characteristics that was identified in the wild-type strain. Addition of this purified metabolite to the growth medium of a mutant strain restored its ability to grow in iron-deficient medium. Furthermore, expression of this gene cluster was induced by growth under iron-limiting conditions, suggesting that expression of this gene cluster occurs when iron is scarce. These data are all consistent with the proposal that the proteins encoded by this gene cluster are involved in the production of a siderophore. Interestingly, these proteins show the highest level of amino acid similarity to proteins from a gene cluster found in the filamentous cyanobacterium Nostoc sp. PCC7120, rather than to known siderophore biosynthetic enzymes. Given these properties, it is proposed that the siderophore produced by A. tumefaciens C58 will have a unique chemical structure. Production of the siderophore was not required for virulence of A. tumefaciens when tested with a standard stem inoculation assay.
利用根癌土壤杆菌C58的全基因组序列，作者鉴定出一个次生代谢物基因簇，该基因簇编码一种具有铁载体活性的代谢物的生物合成。这一结论得到了该基因簇的遗传和调控分析的支持，同时也从根癌土壤杆菌C58中纯化出了一种具有铁螯合活性的代谢物。对该基因簇中被破坏的突变菌株的遗传分析表明，这些菌株在缺铁培养基中的生长速度比野生型菌株慢。此外，突变菌株在液体或固体培养基中均未能产生铬天青S反应性物质，也未能产生野生型菌株中鉴定出的具有铁螯合特性的代谢物。将这种纯化的代谢物添加到突变菌株的生长培养基中，恢复了其在缺铁培养基中生长的能力。此外，该基因簇的表达在铁限制条件下生长时被诱导，这表明该基因簇在铁缺乏时表达。这些数据都与该基因簇编码的蛋白质参与铁载体产生的提议一致。有趣的是，这些蛋白质与丝状蓝细菌念珠藻属PCC7120中发现的一个基因簇的蛋白质具有最高水平的氨基酸相似性，而不是与已知的铁载体生物合成酶相似。鉴于这些特性，有人提出根癌土壤杆菌C58产生的铁载体将具有独特的化学结构。在用标准茎接种试验测试时，根癌土壤杆菌的毒力不需要产生铁载体。
