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首页> 外文期刊>Applied Microbiology >Differential Regulation of the Two Ferrochelatase Paralogues in Shewanella loihica PV-4 in Response to Environmental Stresses
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Differential Regulation of the Two Ferrochelatase Paralogues in Shewanella loihica PV-4 in Response to Environmental Stresses

机译：希瓦氏菌PV-4中两个铁螯合酶类似物对环境胁迫的差异调节。

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Determining the function and regulation of paralogues is important in understanding microbial functional genomics and environmental adaptation. Heme homeostasis is crucial for the survival of environmental microorganisms. Most Shewanella species encode two paralogues of ferrochelatase, the terminal enzyme in the heme biosynthesis pathway. The function and transcriptional regulation of two ferrochelatase genes, hemH1 and hemH2 , were investigated in Shewanella loihica PV-4. The disruption of hemH1 but not hemH2 resulted in a significant accumulation of extracellular protoporphyrin IX (PPIX), the precursor to heme, and decreased intracellular heme levels. hemH1 was constitutively expressed, and the expression of hemH2 increased when hemH1 was disrupted. The transcription of hemH1 was regulated by the housekeeping sigma factor RpoD and potentially regulated by OxyR, while hemH2 appeared to be regulated by the oxidative stress-associated sigma factor RpoE2. When an oxidative stress condition was mimicked by adding H_(2)O_(2) to the medium or exposing the culture to light, PPIX accumulation was suppressed in the Δ hemH1 mutant. Consistently, transcriptome analysis indicated enhanced iron uptake and suppressed heme synthesis in the Δ hemH1 mutant. These data indicate that the two paralogues are functional in the heme synthesis pathway but regulated by environmental conditions, providing insights into the understanding of bacterial response to environmental stresses and a great potential to commercially produce porphyrin compounds.IMPORTANCE Shewanella is capable of utilizing a variety of electron acceptors for anaerobic respiration because of the existence of multiple c -type cytochromes in which heme is an essential component. The cytochrome-mediated electron transfer across cellular membranes could potentially be used for biotechnological purposes, such as electricity generation in microbial fuel cells and dye decolorization. However, the mechanism underlying the regulation of biosynthesis of heme and cytochromes is poorly understood. Our study has demonstrated that two ferrochelatase genes involved in heme biosynthesis are differentially regulated in response to environmental stresses, including light and reactive oxygen species. This is an excellent example showing how bacteria have evolved to maintain cellular heme homeostasis. More interestingly, the high yields of extracellular protoporphyrin IX by the Shewanella loihica PV-4 mutants could be utilized for commercial production of this valuable chemical via bacterial fermentation.
机译：确定旁系同源物的功能和调控对于理解微生物功能基因组学和环境适应性很重要。血红素稳态对环境微生物的生存至关重要。大多数希瓦氏菌物种编码铁螯合酶的两个旁系同源物，即血红素生物合成途径中的末端酶。在Shewanella loihica PV-4中研究了两个铁螯合酶基因hemH1和hemH2的功能和转录调控。 hemH1而不是hemH2的破坏导致血红素的前体细胞外原卟啉IX（PPIX）大量积累，并降低了细胞内血红素水平。 hemH1组成型表达，并且当hemH1受到破坏时，hemH2的表达增加。 hemH1的转录受管家sigma因子RpoD调节，并可能受OxyR调节，而hemH2似乎受氧化应激相关sigma因子RpoE2调节。当通过向培养基中添加H_（2）O_（2）或将培养物暴露在模拟氧化应激条件下时，ΔhemH1突变体中的PPIX积累受到抑制。一致地，转录组分析表明在ΔhemH1突变体中铁吸收增加，血红素合成受到抑制。这些数据表明这两个旁系同源物在血红素合成途径中起作用，但受环境条件调节，为深入理解细菌对环境胁迫的反应提供了见识，并具有商业生产卟啉化合物的巨大潜力。厌氧呼吸的电子受体，因为存在多种血型为必不可少的c型细胞色素。细胞色素介导的跨细胞膜的电子转移可潜在地用于生物技术目的，例如微生物燃料电池中的发电和染料脱色。但是，对血红素和细胞色素的生物合成调节的基本机制了解甚少。我们的研究表明，参与血红素生物合成的两个铁螯合酶基因受环境压力（包括光和活性氧）的影响而受到差异调节。这是一个很好的例子，显示了细菌如何进化来维持细胞血红素的稳态。更有趣的是，Shewanella loihica PV-4突变体的高产量胞外原卟啉IX可用于通过细菌发酵商业生产这种有价值的化学品。

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