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Sinorhizobium meliloti sigma factors RpoE1 and RpoE4 are activated in stationary phase in response to sulfite

机译:苜蓿中华根瘤菌sigma因子RpoE1和RpoE4响应亚硫酸盐而在固定相中被激活

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摘要

Rhizobia are soil bacteria able to establish a nitrogen-fixing symbiosis with legume plants. Both in soil and in planta, rhizobia spend non-growing periods resembling the stationary phase of in vitro-cultured bacteria. The primary objective of this work was to better characterize gene regulation in this biologically relevant growth stage in Sinorhizobium meliloti. By a tap-tag/mass spectrometry approach, we identified five sigma factors co-purifying with the RNA polymerase in stationary phase: the general stress response regulator RpoE2, the heat shock sigma factor RpoH2, and three extra-cytoplasmic function sigma factors (RpoE1, RpoE3 and RpoE4) belonging to the poorly characterized ECF26 subgroup. We then showed that RpoE1 and RpoE4 i) are activated upon metabolism of sulfite-generating compounds (thiosulfate and taurine), ii) display overlapping regulatory activities, iii) govern a dedicated sulfite response by controlling expression of the sulfite dehydrogenase SorT, iv) are activated in stationary phase, likely as a result of endogenous sulfite generation during bacterial growth. We showed that SorT is required for optimal growth of S. meliloti in the presence of sulfite, suggesting that the response governed by RpoE1 and RpoE4 may be advantageous for bacteria in stationary phase either by providing a sulfite detoxification function or by contributing to energy production through sulfite respiration. This paper therefore reports the first characterization of ECF26 sigma factors, the first description of sigma factors involved in control of sulphur metabolism, and the first indication that endogenous sulfite may act as a signal for regulation of gene expression upon entry of bacteria in stationary phase.
机译:根瘤菌是能够与豆类植物建立固氮共生的土壤细菌。在土壤和植物中,根瘤菌的生长期都与体外培养细菌的静止期相似。这项工作的主要目的是更好地表征melinohizobium meliloti在此生物学相关的生长阶段的基因调控。通过轻敲标签/质谱法,我们鉴定了与固定相中的RNA聚合酶共同纯化的5个sigma因子:一般应激反应调节剂RpoE2,热休克sigma因子RpoH2和三个胞浆外功能sigma因子(RpoE1 ,RpoE3和RpoE4)属于特征较弱的ECF26亚组。然后,我们显示RpoE1和RpoE4 i)在生成亚硫酸盐的化合物(硫代硫酸盐和牛磺酸)代谢时被激活,ii)显示重叠的调节活性,iii)通过控制亚硫酸盐脱氢酶SorT的表达来控制专用的亚硫酸盐响应,iv)可能在细菌生长过程中产生内源性亚硫酸盐,因此在固定相中被激活。我们表明,在亚硫酸盐存在下,SorT是苜蓿链球菌最佳生长所必需的,这表明由RpoE1和RpoE4控制的响应可能通过提供亚硫酸盐解毒功能或通过促进能量生产而对固定相中的细菌有利。亚硫酸盐呼吸。因此,本文报道了ECF26σ因子的第一个特征,涉及硫代谢控制的σ因子的第一个描述,以及内源性亚硫酸盐可能在细菌进入固定相时作为调节基因表达的信号的第一个指示。

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