Department of Microbiology and Immunology, The Brody School of Medicine at East Carolina University, 600 Moye Blvd., Greenville, NC 27834, USA.
J Bacteriol. 2011 Dec;193(23):6567-75. doi: 10.1128/JB.05803-11. Epub 2011 Sep 30.
The opportunistic pathogen Pseudomonas aeruginosa can utilize a variety of carbon sources and produces many secondary metabolites to help survive harsh environments. P. aeruginosa is part of a small group of bacteria that use the kynurenine pathway to catabolize tryptophan. Through the kynurenine pathway, tryptophan is broken down into anthranilate, which is further degraded into tricarboxylic acid cycle intermediates or utilized to make numerous aromatic compounds, including the Pseudomonas quinolone signal (PQS). We have previously shown that the kynurenine pathway is a critical source of anthranilate for PQS synthesis and that the kynurenine pathway genes (kynA and kynBU) are upregulated in the presence of kynurenine. A putative Lrp/AsnC-type transcriptional regulator (gene PA2082, here called kynR), is divergently transcribed from the kynBU operon and is highly conserved in gram-negative bacteria that harbor the kynurenine pathway. We show that a mutation in kynR renders P. aeruginosa unable to utilize L-tryptophan as a sole carbon source and decreases PQS production. In addition, we found that the increase of kynA and kynB transcriptional activity in response to kynurenine was completely abolished in a kynR mutant, further indicating that KynR mediates the kynurenine-dependent expression of the kynurenine pathway genes. Finally, we found that purified KynR specifically bound the kynA promoter in the presence of kynurenine and bound the kynB promoter in the absence or presence of kynurenine. Taken together, our data show that KynR directly regulates the kynurenine pathway genes.
机会性病原体铜绿假单胞菌可以利用多种碳源,并产生许多次生代谢物来帮助其在恶劣环境中生存。铜绿假单胞菌是一小部分利用犬尿氨酸途径分解色氨酸的细菌之一。通过犬尿氨酸途径,色氨酸被分解成邻氨基苯甲酸,邻氨基苯甲酸进一步降解为三羧酸循环中间产物,或用于合成许多芳香族化合物,包括铜绿假单胞菌喹诺酮信号(PQS)。我们之前已经表明,犬尿氨酸途径是 PQS 合成的邻氨基苯甲酸的关键来源,并且犬尿氨酸途径基因(kynA 和 kynBU)在犬尿氨酸存在下上调。一个假定的 Lrp/AsnC 型转录调节因子(基因 PA2082,此处称为 kynR),与 kynBU 操纵子反方向转录,并且在具有犬尿氨酸途径的革兰氏阴性菌中高度保守。我们表明,kynR 突变使铜绿假单胞菌无法将 L-色氨酸用作唯一碳源,并降低 PQS 产量。此外,我们发现,在 kynR 突变体中,对犬尿氨酸的响应中 kynA 和 kynB 转录活性的增加完全被消除,这进一步表明 KynR 介导了犬尿氨酸途径基因的犬尿氨酸依赖性表达。最后,我们发现,纯化的 KynR 在存在犬尿氨酸的情况下特异性结合 kynA 启动子,并在不存在或存在犬尿氨酸的情况下结合 kynB 启动子。总之,我们的数据表明 KynR 直接调节犬尿氨酸途径基因。