Gralnick Jeffrey A, Brown C Titus, Newman Dianne K
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Mol Microbiol. 2005 Jun;56(5):1347-57. doi: 10.1111/j.1365-2958.2005.04628.x.
Shewanella oneidensis strain MR-1 is well known for its respiratory versatility, yet little is understood about how it regulates genes involved in anaerobic respiration. The Arc two-component system plays an important role in this process in Escherichia coli; therefore, we determined its function in S. oneidensis. arcA from S. oneidensis complements an E. coli arcA mutant, but the Arc regulon in S. oneidensis constitutes a different suite of genes. For example, one of the strongest ArcA-regulated gene clusters in E. coli, sdh, is not regulated by the Arc system in S. oneidensis, and the cyd locus, which is induced by ArcA in E. coli under microaerobic conditions, is repressed by ArcA in S. oneidensis under anaerobic conditions. One locus that we identified as being potentially regulated by ArcA in S. oneidensis contains genes predicted to encode subunits of a dimethyl sulphoxide (DMSO) reductase. We demonstrate that these genes encode a functional DMSO reductase, and that an arcA mutant cannot fully induce their expression and is defective in growing on DMSO under anaerobic conditions. While S. oneidensis lacks a highly conserved full-length ArcB homologue, ArcA is partially activated by a small protein homologous to the histidine phosphotransfer domain of ArcB from E. coli, HptA. This protein alone is unable to compensate for the lack of arcB in E. coli, indicating that another protein is required in addition to HptA to activate ArcA in S. oneidensis.
奥奈达希瓦氏菌MR-1菌株以其呼吸多样性而闻名，但对于它如何调控参与厌氧呼吸的基因却知之甚少。Arc双组分系统在大肠杆菌的这一过程中发挥着重要作用；因此，我们确定了它在奥奈达希瓦氏菌中的功能。奥奈达希瓦氏菌的arcA可互补大肠杆菌的arcA突变体，但奥奈达希瓦氏菌中的Arc调控子由不同的基因组合构成。例如，大肠杆菌中受ArcA调控最强的基因簇之一——sdh，在奥奈达希瓦氏菌中不受Arc系统调控，而在大肠杆菌中微需氧条件下由ArcA诱导的cyd位点，在奥奈达希瓦氏菌厌氧条件下却受ArcA抑制。我们在奥奈达希瓦氏菌中鉴定出一个可能受ArcA调控的位点，其中包含预测编码二甲基亚砜（DMSO）还原酶亚基的基因。我们证明这些基因编码一种功能性DMSO还原酶，并且arcA突变体不能完全诱导它们的表达，在厌氧条件下利用DMSO生长存在缺陷。虽然奥奈达希瓦氏菌缺乏高度保守的全长ArcB同源物，但ArcA可被一种与大肠杆菌ArcB的组氨酸磷酸转移结构域同源的小蛋白HptA部分激活。单独这种蛋白无法弥补大肠杆菌中arcB的缺失，这表明在奥奈达希瓦氏菌中除HptA外还需要另一种蛋白来激活ArcA。
