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Norambuena, J, Hanson, TE, Barkay, T and Boyd, JM (2019) Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool. MBio 10


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 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 Δ Δ and Δ Δ double mutant strains were as sensitive to Hg(II) as the Δ strain that lacks bacillithiol, suggesting that the increased sensitivity to Hg(II) in the Δ and Δ mutant strains is due to a decrease of reduced BSH. Treatment of with Hg(II) decreased aconitase activity and increased the intracellular concentration of free Fe, and these phenotypes were exacerbated in Δ and Δ 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 to effectively metabolize ROS generated as a normal consequence of growth in aerobic environments. is a deep-branching thermophilic aerobe. It is a member of the - phylum that, together with the , constitute the earliest branching aerobic bacterial lineages; therefore, this organism serves as a model for early diverged bacteria (R. K. Hartmann, J. Wolters, B. Kröger, 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). likely arose shortly after the oxidation of the biosphere 2.4 billion years ago. Studying 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.


PubMed PMC6445937 Online version:10.1128/mBio.00183-19




Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status


GO:0071793: bacillithiol biosynthetic process

ECO:0001272: high-performance liquid chromatography evidence used in manual assertion


In Δsod Thermus thermophilus mutants, HPLC is used to observe a statistically significant drop in reduced bacillthiol pools (BSH), despite the total BSH (oxidized and reduced) concentrations remaining the same. Sod (superoxide dismutase) is a well-characterized antioxidant enzyme and its deletion, combined with the difference in reduced BSH levels, suggests Sod plays a role in BSH oxidation.

CACAO 13753


See also


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