College of Biological Sciences, China Agricultural University, Beijing 100094, China.
BMC Microbiol. 2010 Feb 8;10:36. doi: 10.1186/1471-2180-10-36.
Soil microorganisms are mainly responsible for the complete mineralization of aromatic compounds that usually originate from plant products or environmental pollutants. In many cases, structurally diverse aromatic compounds can be converted to a small number of structurally simpler intermediates, which are metabolized to tricarboxylic acid intermediates via the beta-ketoadipate pathway. This strategy provides great metabolic flexibility and contributes to increased adaptation of bacteria to their environment. However, little is known about the evolution and regulation of the beta-ketoadipate pathway in root-associated diazotrophs.
In this report, we performed a genome-wide analysis of the benzoate and 4-hydroxybenzoate catabolic pathways of Pseudomonas stutzeri A1501, with a focus on the functional characterization of the beta-ketoadipate pathway. The P. stutzeri A1501 genome contains sets of catabolic genes involved in the peripheral pathways for catabolism of benzoate (ben) and 4-hydroxybenzoate (pob), and in the catechol (cat) and protocatechuate (pca) branches of the beta-ketoadipate pathway. A particular feature of the catabolic gene organization in A1501 is the absence of the catR and pcaK genes encoding a LysR family regulator and 4-hydroxybenzoate permease, respectively. Furthermore, the BenR protein functions as a transcriptional activator of the ben operon, while transcription from the catBC promoter can be activated in response to benzoate. Benzoate degradation is subject to carbon catabolite repression induced by glucose and acetate in A1501. The HPLC analysis of intracellular metabolites indicated that low concentrations of 4-hydroxybenzoate significantly enhance the ability of A1501 to degrade benzoate.
The expression of genes encoding proteins involved in the beta-ketoadipate pathway is tightly modulated by both pathway-specific and catabolite repression controls in A1501. This strain provides an ideal model system for further study of the evolution and regulation of aromatic catabolic pathways.
土壤微生物主要负责芳香族化合物的完全矿化，这些化合物通常来源于植物产物或环境污染物。在许多情况下，结构多样的芳香族化合物可以转化为少数结构更简单的中间产物，这些中间产物通过β-酮己二酸途径代谢为三羧酸中间产物。这种策略提供了巨大的代谢灵活性，并有助于细菌更好地适应其环境。然而，对于与根相关的固氮菌中β-酮己二酸途径的进化和调控知之甚少。
在本报告中，我们对施氏假单胞菌 A1501 的苯甲酸和 4-羟基苯甲酸代谢途径进行了全基因组分析，重点研究了β-酮己二酸途径的功能特征。施氏假单胞菌 A1501 基因组包含参与苯甲酸（ben）和 4-羟基苯甲酸（pob）外周代谢途径以及β-酮己二酸途径中的儿茶酚（cat）和原儿茶酸（pca）分支的代谢基因。A1501 中代谢基因组织的一个显著特点是缺少编码 LysR 家族调节剂和 4-羟基苯甲酸透酶的 catR 和 pcaK 基因。此外，BenR 蛋白作为 ben 操纵子的转录激活因子发挥作用，而 catBC 启动子的转录可以响应苯甲酸而被激活。在 A1501 中，苯甲酸降解受到葡萄糖和醋酸盐的碳分解代谢物阻遏的影响。细胞内代谢物的 HPLC 分析表明，低浓度的 4-羟基苯甲酸显著增强了 A1501 降解苯甲酸的能力。
施氏假单胞菌 A1501 中参与β-酮己二酸途径的基因表达受途径特异性和分解代谢物阻遏控制的严格调控。该菌株为进一步研究芳香族代谢途径的进化和调控提供了理想的模型系统。
