Listeria monocytogenes is a fastidious bacterial pathogen that can utilize only a limited number of nitrogen sources for growth. Both glutamine and ammonium are common nitrogen sources used in listerial defined growth media, but little is known about the regulation of their uptake or utilization. The functional role of L. monocytogenes GlnR, the transcriptional regulator of nitrogen metabolism genes in low-G+C Gram-positive bacteria, was determined using transcriptome sequencing and real-time reverse transcription-PCR experiments. The GlnR regulon included transcriptional units involved in ammonium transport (amtB glnK) and biosynthesis of glutamine (glnRA) and glutamate (gdhA) from ammonium. As in other bacteria, GlnR proved to be an autoregulatory repressor of the glnRA operon. Unexpectedly, GlnR was most active during growth with ammonium as the nitrogen source and less active in the glutamine medium, apparently because listerial cells perceive growth with glutamine as a nitrogen-limiting condition. Therefore, paradoxically, expression of the glnA gene, encoding glutamine synthetase, was highest in the glutamine medium. For the amtB glnK operon, GlnR served as both a negative regulator in the presence of ammonium and a positive regulator in the glutamine medium. The gdhA gene was subject to a third mode of regulation that apparently required an elevated level of GlnR for repression. Finally, activity of glutamate dehydrogenase encoded by the gdhA gene appeared to correlate inversely with expression of gltAB, the operon that encodes the other major glutamate-synthesizing enzyme, glutamate synthase. Both gdhA and amtB were also regulated, in a negative manner, by the global transcriptional regulator CodY.

中文翻译：

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GlnR在控制单核细胞增生李斯特菌中氮代谢基因表达中的作用。

单核细胞增生利斯特氏菌是一种挑剔的细菌病原体，只能利用有限数量的氮源进行生长。谷氨酰胺和铵都是在利斯特氏菌生长培养基中常用的氮源，但对其吸收或利用的调控知之甚少。的功能作用李斯特菌GlnR，氮代谢基因在低G + C革兰氏阳性菌的转录调节，使用转录组测序和实时逆转录PCR实验测定。GlnR调节子包括参与铵转运（amtB glnK）和谷氨酰胺（glnRA）和谷氨酸（gdhA）生物合成的转录单位。）。与其他细菌一样，GlnR被证明是glnRA操纵子的自动调节阻遏物。出乎意料的是，GlnR在以铵盐为氮源的生长过程中活性最高，而在谷氨酰胺培养基中的活性较低，这显然是因为李斯特菌细胞将谷氨酰胺作为氮限制条件而感知生长。因此，矛盾的是，编码谷氨酰胺合成酶的glnA基因的表达在谷氨酰胺培养基中最高。对于amtB glnK操纵子，GlnR在存在铵的情况下既充当负调节剂，又在谷氨酰胺培养基中充当正调节剂。该gdhA基该基因受到第三种调控方式的作用，显然需要升高水平的GlnR才能进行抑制。最后，由gdhA基因编码的谷氨酸脱氢酶的活性似乎与gltAB的表达呈反相关，gltAB是编码另一种主要谷氨酸合成酶谷氨酸合酶的操纵子。无论gdhA基和amtB也规定，在负的方式，通过了全球转录调节科迪。