Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, 28049, Spain.
Department of Molecular Biology, Umeå University, Umeå, 901 87, Sweden.
Environ Microbiol. 2018 Oct;20(10):3851-3861. doi: 10.1111/1462-2920.14400. Epub 2018 Oct 2.
In many Thermus thermophilus strains, nitrate respiration is encoded in mobile genetic regions, along with regulatory circuits that modulate its expression based on anoxia and nitrate presence. The oxygen-responsive system has been identified as the product of the dnrST (dnr) operon located immediately upstream of the nar operon (narCGHJIKT), which encodes the nitrate reductase (NR) and nitrate/nitrite transporters. In contrast, the nature of the nitrate sensory system is not known. Here, we analyse the putative nitrate-sensing role of the bicistronic drp operon (drpAB) present downstream of the nar operon in most denitrifying Thermus spp. Expression of drp was found to depend on the master regulator DnrT, whereas the absence of DrpA or DrpB increased the expression of both DnrS and DnrT and, concomitantly, of the NR. Absence of both proteins made expression from the dnr and nar operons independent of nitrate. Polyclonal antisera allowed us to identify DrpA as a periplasmic protein and DrpB as a membrane protein, with capacity to bind to the cytoplasmic membrane. Here, we propose a role for DrpA/DrpB as nitrate sensors during denitrification.
在许多嗜热栖热菌菌株中，硝酸盐呼吸是由移动遗传区域编码的，同时还有调节电路，根据缺氧和硝酸盐的存在来调节其表达。氧气响应系统已被确定为位于硝酸盐还原酶（NR）和硝酸盐/亚硝酸盐转运蛋白编码的nar 操纵子（narCGHJIKT）上游的 dnrST（dnr）操纵子的产物。相比之下，硝酸盐感应系统的性质尚不清楚。在这里，我们分析了大多数反硝化嗜热菌属中位于 nar 操纵子下游的双顺反子 drp 操纵子（drpAB）的假定硝酸盐感应作用。发现 drp 的表达依赖于主调控因子 DnrT，而 DrpA 或 DrpB 的缺失增加了 DnrS 和 DnrT 的表达，并相应地增加了 NR 的表达。两种蛋白质的缺失使 dnr 和 nar 操纵子的表达都不依赖于硝酸盐。多克隆抗血清允许我们鉴定 DrpA 为周质蛋白，DrpB 为膜蛋白，具有与细胞质膜结合的能力。在这里，我们提出了 DrpA/DrpB 在反硝化过程中作为硝酸盐传感器的作用。
