Institute of Microbiology and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China.
Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong, China.
Appl Environ Microbiol. 2018 Apr 2;84(8). doi: 10.1128/AEM.00039-18. Print 2018 Apr 15.
Iron, a major protein cofactor, is essential for most organisms but can simultaneously be toxic. Iron homeostasis thus has to be effectively maintained under a range of iron regimes. This may be particularly true with , a representative of dissimilatory metal-reducing bacteria (DMRB), which are capable of respiring a variety of chemicals as electron acceptors (EAs), including iron ores. Although iron respiration and its regulation have been extensively studied in this bacterium, how iron homeostasis is maintained remains largely unknown. Here, we report that the loss of the iron homeostasis master regulator Fur negatively affects the respiration of all EAs tested. This defect appears mainly to be a result of reduced cytochrome (cyt ) production, despite a decrease in the expression of reductases that are under the direct control of Fur. We also show that Fur interacts with canonical Fur box motifs in F-F-x-R configuration rather than the palindromic motif proposed before. The mutant has lowered total iron and increased free iron contents. Under iron-rich conditions, overproduction of the major iron storage protein Bfr elevates the total iron levels of the mutant over those of the wild-type but does not affect free iron levels. Intriguingly, such an operation only marginally improves cyt production by affecting heme biosynthesis. It is established that iron dictates heme /cyt biosynthesis in strains, but the mutation annuls the dependence of heme /cyt biosynthesis on iron. Overall, our results suggest that Fur has a profound impact on the iron homeostasis of , through which many physiological processes, especially respiration, are transformed. Iron reduction is a signature of , and this process relies on a large number of type cytochromes, which are iron-containing proteins. Thus, iron plays an essential and special role in iron respiration, but to date, the nature of iron metabolism and regulation of the bacterium remains largely unknown. In this study, we investigated impacts of Fur, the master regulator of iron homeostasis, on respiration. The loss of Fur causes a general defect in respiration, a result of impaired cyt production rather than specific regulation. Additionally, the mutant is unresponsive to iron, resulting in imbalanced iron homeostasis and dissociation between iron and cyt production. These findings provide important insights into the iron biology of DMRB.
铁是大多数生物体必需的主要蛋白质辅因子，但同时也具有毒性。因此，在一系列铁环境中，铁的动态平衡必须得到有效维持。对于异化金属还原菌（DMRB）的代表 来说，这可能尤其如此，它可以将多种化学物质作为电子受体（EA）进行呼吸，包括铁矿石。尽管在这种细菌中已经广泛研究了铁呼吸及其调节，但铁动态平衡是如何维持的仍然知之甚少。在这里，我们报告说，铁动态平衡主调控因子 Fur 的缺失会对所有测试的 EA 的呼吸产生负面影响。这种缺陷主要似乎是由于细胞色素 （cyt ）产生减少所致，尽管受 Fur 直接控制的还原酶的表达减少。我们还表明， Fur 与经典 Fur 盒基序以 F-F-x-R 构型相互作用，而不是以前提出的回文基序。突变体的总铁含量降低，游离铁含量增加。在富铁条件下，主要铁储存蛋白 Bfr 的过量产生使 突变体的总铁水平高于野生型，但不影响游离铁水平。有趣的是，这种操作仅通过影响血红素生物合成来略微改善 cyt 产生。已经确定铁在 菌株中决定血红素 /细胞色素 生物合成，但 突变消除了血红素 /细胞色素 生物合成对铁的依赖。总体而言，我们的结果表明，Fur 对 的铁动态平衡有深远影响，通过它，许多生理过程，特别是呼吸，都发生了变化。铁还原是 的特征，这个过程依赖于大量的类型 细胞色素， 是含铁蛋白。因此，铁在铁呼吸中起着至关重要和特殊的作用，但迄今为止，该细菌的铁代谢性质和调控仍知之甚少。在这项研究中，我们研究了铁动态平衡的主调控因子 Fur 对呼吸的影响。Fur 的缺失会导致呼吸普遍缺陷，这是由于 cyt 产生受损而不是特定调节所致。此外， 突变体对铁无反应，导致铁动态平衡失衡，铁与 cyt 产生分离。这些发现为 DMRB 的铁生物学提供了重要的见解。
