Rhodopseudomonas palustris is a purple, facultatively phototrophic bacterium that uses hydrogen gas as an electron donor for carbon dioxide fixation during photoautotrophic growth or for ammonia synthesis during nitrogen fixation. It also uses hydrogen as an electron supplement to enable the complete assimilation of oxidized carbon compounds, such as malate, into cell material during photoheterotrophic growth. The R. palustris genome predicts a membrane-bound nickel-iron uptake hydrogenase and several regulatory proteins to control hydrogenase synthesis. There is also a novel sensor kinase gene (RPA0981) directly adjacent to the hydrogenase gene cluster. Here we show that the R. palustris regulatory sensor hydrogenase HupUV acts in conjunction with the sensor kinase-response regulator protein pair HoxJ-HoxA to activate hydrogenase expression in response to hydrogen gas. Transcriptome analysis indicated that the HupUV-HoxJA regulatory system also controls the expression of genes encoding a predicted dicarboxylic acid transport system, a putative formate transporter, and a glutamine synthetase. RPA0981 had a small effect in repressing hydrogenase synthesis. We also determined that the two-component system RegS-RegR repressed expression of the uptake hydrogenase, probably in response to changes in intracellular redox status. Transcriptome analysis indicated that about 30 genes were differentially expressed in R. palustris cells that utilized hydrogen when growing photoheterotrophically on malate under nitrogen-fixing conditions compared to a mutant strain that lacked uptake hydrogenase. From this it appears that the recycling of reductant in the form of hydrogen does not have extensive nonspecific effects on gene expression in R. palustris.

译文

红假单胞菌 (Rhodopseudomonas palustris) 是一种紫色的兼性光养细菌,在光自养生长过程中使用氢气作为电子供体进行二氧化碳固定或在固氮过程中进行氨合成。它还使用氢作为电子补充剂,以使氧化的碳化合物 (例如苹果酸盐) 在光异养生长过程中完全同化为细胞材料。R. palustris基因组预测了膜结合的镍铁吸收氢化酶和几种控制氢化酶合成的调节蛋白。还有一个新的传感器激酶基因 (RPA0981) 直接与氢化酶基因簇相邻。在这里,我们显示了R. palustris调节传感器氢化酶HupUV与传感器激酶响应调节蛋白对HoxJ-HoxA共同作用,以响应氢气激活氢化酶表达。转录组分析表明,HupUV-HoxJA调节系统还控制编码预测的二羧酸转运系统,推定的甲酸转运蛋白和谷氨酰胺合成酶的基因的表达。RPA0981在抑制氢化酶合成方面的作用很小。我们还确定,两组分系统RegS-RegR抑制了摄取氢化酶的表达,可能是对细胞内氧化还原状态变化的响应。转录组分析表明,与缺乏摄取氢化酶的突变菌株相比,在固氮条件下在苹果酸上光异养生长时利用氢的R. palustris细胞中约30个基因差异表达。由此看来,以氢形式回收还原剂对R. palustris的基因表达没有广泛的非特异性影响。

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