School of Life Science, Northeast Agricultural University, Harbin 150030, China.
Res Microbiol. 2012 Jun;163(5):332-9. doi: 10.1016/j.resmic.2012.05.002. Epub 2012 May 29.
The nitrogen-fixing Pseudomonas stutzeri strain A1501 contains two ammonium transporter genes, amtB1 and amtB2, linked to glnK. Growth of an amtB1-amtB2 double deletion mutant strain was not impaired compared to that of the wild type under any conditions tested, and it was still capable of taking up ammonium ions at nearly wild-type rates. Nitrogenase activity was repressed in wild-type strain A1501 in response to the addition of ammonium, but nitrogenase activity was only partially impaired in the amtB1 and amtB2 double mutant, suggesting that the two AmtB proteins are involved in regulating expression of nitrogenase or its activity in response to ammonium. An interaction between GlnK and AmtB1 or AmtB2 was observed in a yeast two-hybrid assay. Ammonium was excreted by the amtB double mutant strain under nitrogen fixation conditions, particularly when nifA was expressed constitutively. This suggests that AmtB proteins play a role in controlling the internal pool of ammonia within the cell.
固氮假单胞菌 A1501 菌株含有两个铵转运基因 amtB1 和 amtB2，与 glnK 相连。与野生型相比，在测试的任何条件下，amtB1-amtB2 双缺失突变菌株的生长都没有受到损害，并且仍然能够以接近野生型的速率吸收铵离子。氮固定酶活性在野生型菌株 A1501 中受到铵的添加的抑制，但氮固定酶活性在 amtB1 和 amtB2 双突变体中仅部分受损，表明这两种 AmtB 蛋白参与调节氮固定酶或其对铵的活性的表达。在酵母双杂交测定中观察到 GlnK 与 AmtB1 或 AmtB2 之间的相互作用。在氮固定条件下，特别是当 nifA 组成型表达时，amtB 双突变菌株会排泄铵。这表明 AmtB 蛋白在控制细胞内氨的内部池方面发挥作用。
