Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Department of Environmental Protection, E-18008 Granada, Spain.
Environ Microbiol. 2010 Jun;12(6):1427-38. doi: 10.1111/j.1462-2920.2009.02124.x. Epub 2009 Dec 27.
Pseudomonas putida is a soil microorganism that utilizes aromatic amino acids present in root exudates as a nitrogen source. We have previously shown that the PhhR transcriptional regulator induces phhAB genes encoding a phenylalanine hydroxylase. In this study we show, using microarray assays and promoter fusions, that PhhR is a global regulator responsible for the activation of genes essential for phenylalanine degradation, phenylalanine homeostasis and other genes of unknown function. Recently, it has been shown that phenylalanine catabolism occurs through more than one pathway. One of these possible pathways involves the metabolism of phenylalanine via tyrosine, p-hydroxyphenylpyruvate, and homogentisate. We identified two genes within this pathway that encode an acyl-CoA transferase involved in the metabolism of acetoacetate. All genes in this pathway were induced in response to phenylalanine in a PhhR-proficient background. The second potential degradative pathway involves the degradation of phenylalanine to produce phenylpyruvate, which seems to be degraded via phenylacetyl-CoA. A number of mutants in the paa genes encoding phenylacetyl-CoA degradation enzymes fail to grow on phenylpyruvate or phenylacetate, further supporting the existence of this second pathway. We found that the PhhR regulon also includes genes involved in the biosynthesis of aromatic amino acids that are repressed in the presence of phenylalanine, suggesting the possibility of feedback at the transcriptional level. In addition, we found that PhhR modulates the level of expression of the broad-substrate-specificity MexEF/OprN efflux pump. Expression from this pump is under the control of mexT gene product because phenylalanine-dependent transcription from the mexE promoter does not occur in a mexT mutant background. These results place PhhR as an important regulator in the control of bacterial responses to aromatic amino acids.
铜绿假单胞菌是一种土壤微生物，它利用根分泌物中存在的芳香族氨基酸作为氮源。我们之前已经表明，PhhR 转录调节剂诱导编码苯丙氨酸羟化酶的 phhAB 基因。在这项研究中，我们使用微阵列分析和启动子融合实验表明，PhhR 是一个全局调节剂，负责激活苯丙氨酸降解、苯丙氨酸稳态和其他未知功能基因所必需的基因。最近，已经表明苯丙氨酸代谢可以通过不止一种途径进行。其中一种可能的途径涉及通过酪氨酸、对羟基苯丙酮酸和高丝氨酸代谢苯丙氨酸。我们在这个途径中鉴定了两个基因，它们编码参与乙酰辅酶 A 代谢的酰基辅酶 A 转移酶。在 PhhR 功能齐全的背景下，这个途径中的所有基因都能响应苯丙氨酸而被诱导。第二个潜在的降解途径涉及苯丙氨酸降解产生苯丙酮酸，苯丙酮酸似乎通过苯乙酰辅酶 A 降解。编码苯乙酰辅酶 A 降解酶的多个 paa 基因的突变体不能在苯丙酮酸或苯乙酸上生长，这进一步支持了第二种途径的存在。我们发现 PhhR 调控子还包括参与芳香族氨基酸生物合成的基因，这些基因在苯丙氨酸存在时受到抑制，这表明在转录水平上可能存在反馈。此外，我们发现 PhhR 调节广谱特异性 MexEF/OprN 外排泵的表达水平。由于 mexT 突变体背景下不存在依赖苯丙氨酸的 mexE 启动子转录，因此该泵的表达受 mexT 基因产物的控制。这些结果表明 PhhR 是控制细菌对芳香族氨基酸反应的重要调节剂。
