Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool
Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool
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DOI：
10.1128/mbio.00183-19
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发表时间：
2019-03-01
期刊：
影响因子：
6.4
通讯作者：
Boyd, Jeffrey M.
中科院分区：
文献类型：
--
作者：
Norambuen, Javiera;Hanson, Thomas E.;Boyd, Jeffrey M.
汞(Hg)是一种分布广泛、有毒的重金属，其细胞作用未知。汞毒性与活性氧物种(ROS)的产生有关，但汞不直接与氧进行氧化还原化学作用。暴露在离子形式汞(II)中如何产生ROS尚不清楚。嗜热嗜热菌暴露于汞(II)可引起ROS的积累，超氧化物歧化酶(SOD)和假过氧化氢酶(PCAT)的转录和活性增加，但汞(II)使超氧化物歧化酶和PCAT失活。缺乏SOD或PCAT的菌株比野生型菌株具有更高的氧化杆菌硫醇(BSH)水平，并且对Hg(II)更敏感。Delta BSHA Delta sod和Delta BSHA Delta PCAT双突变菌株对Hg(II)的敏感性与Delta BSHA缺乏杆菌硫醇的Delta BSHA菌株一样敏感，这表明Delta sod和Delta PCAT突变菌株对Hg(II)的敏感性增加是由于BSH降低。嗜热链霉菌经Hg(II)处理后，乌头酸酶活性降低，胞内游离铁浓度升高，并且在Delta sod和Delta pCAT突变株中这些表型加重。汞(II)处理也增加了DNA损伤。我们的结论是，汞(II)对氧化还原缓冲硫醇BSH的隔离，以及对ROS清除酶的直接灭活，削弱了嗜热假单胞菌有效代谢ROS的能力，这是在有氧环境中生长的正常结果。它是嗜热球菌门的一员，与水生生物一起构成了最早的分枝需氧细菌谱系；因此，这种生物作为早期分流细菌的模型(R.K.Hartmann，J.Wolters，B.Kroger，S.Schultze，等，Syst Appl Microbiol11：243-249,1989，https://doi.org/10.1016/S0723-2020(89)80020-7)，其自然加热的栖息地可能包含地质来源的汞(G.G.Geesey，T.Barkay，和S.King，Sci Total Envion569-570：321-331,2016，https://doi.org/10.1016/j.scitotenv.2016.06.080).嗜热梭菌可能是在24亿年前生物圈氧化后不久出现的。对嗜热梭菌生理学的研究为汞和氧化应激反应机制的起源和进化提供了线索，后者对所有现存的好氧菌的生存和功能至关重要。
Mercury (Hg) is a widely distributed, toxic heavy metal with no known cellular role. Mercury toxicity has been linked to the production of reactive oxygen species (ROS), but Hg does not directly perform redox chemistry with oxygen. How exposure to the ionic form, Hg(II), generates ROS is unknown. Exposure of Thermus thermophilus to Hg(II) triggered ROS accumulation and increased transcription and activity of superoxide dismutase (Sod) and pseudocatalase (Pcat); however, Hg(II) inactivated Sod and Pcat. Strains lacking Sod or Pcat had increased oxidized bacillithiol (BSH) levels and were more sensitive to Hg(II) than the wild type. The Delta bshA Delta sod and Delta bshA Delta pcat double mutant strains were as sensitive to Hg(II) as the Delta bshA strain that lacks bacillithiol, suggesting that the increased sensitivity to Hg(II) in the Delta sod and Delta pcat mutant strains is due to a decrease of reduced BSH. Treatment of T. thermophilus with Hg(II) decreased aconitase activity and increased the intracellular concentration of free Fe, and these phenotypes were exacerbated in Delta sod and Delta pcat mutant strains. Treatment with Hg(II) also increased DNA damage. We conclude that sequestration of the redox buffering thiol BSH by Hg(II), in conjunction with direct inactivation of ROS-scavenging enzymes, impairs the ability of T. thermophilus to effectively metabolize ROS generated as a normal consequence of growth in aerobic environments.IMPORTANCE Thermus thermophilus is a deep-branching thermophilic aerobe. It is a member of the Deinococcus-Thermus phylum that, together with the Aquificae, constitute the earliest branching aerobic bacterial lineages; therefore, this organism serves as a model for early diverged bacteria (R. K. Hartmann, J. Wolters, B. Kroger, S. Schultze, et al., Syst Appl Microbiol 11:243-249, 1989, https://doi.org/10.1016/S0723-2020(89)80020-7) whose natural heated habitat may contain mercury of geological origins (G. G. Geesey, T. Barkay, and S. King, Sci Total Environ 569-570:321-331, 2016, https://doi.org/10.1016/j.scitotenv.2016.06.080). T. thermophilus likely arose shortly after the oxidation of the biosphere 2.4 billion years ago. Studying T. thermophilus physiology provides clues about the origin and evolution of mechanisms for mercury and oxidative stress responses, the latter being critical for the survival and function of all extant aerobes.