Role of MerH in mercury resistance in the archaeon Sulfolobus solfataricus

Abstract

Crenarchaeota include extremely thermoacidophilic organisms that thrive in geothermal environments dominated by sulfidic ores and heavy metals such as mercury. Mercuric ion, Hg(II), inactivates transcription in the crenarchaeote Sulfolobus solfataricus and simultaneously derepresses transcription of a resistance operon, merHAI, through interaction with the MerR transcription factor. While mercuric reductase (MerA) is required for metal resistance, the role of MerH, an adjacent small and predicted product of an ORF, has not been explored. Inactivation of MerH either by nonsense mutation or by in-frame deletion diminished Hg(II) resistance of mutant cells. Promoter mapping studies indicated that Hg(II) sensitivity of the merH nonsense mutant arose through transcriptional polarity, and its metal resistance was restored partially by single copy merH complementation. Since MerH was not required in vitro for MerA-catalysed Hg(II) reduction, MerH may play an alternative role in metal resistance. Inductively coupled plasma-mass spectrometry analysis of the MerH deletion strain following metal challenge indicated that there was prolonged retention of intracellular Hg(II). Finally, a reduced rate of mer operon induction in the merH deletion mutant suggested that the requirement for MerH could result from metal trafficking to the MerR transcription factor.

Identification of an archaeal mercury regulon by chromatin immunoprecipitation

“…6b). As observed previously, the merA mutant accumulated the highest levels of mercury during the metal challenge period (Schelert et al, 2013), consistent with the loss of mercuric reductase. As an additional control, the intracellular levels of molybdenum were examined in the same cell extracts during the mercury treatment time course.…”

“…Together with its location immediately adjacent to mercuric reductase (MerA), merH was implicated as playing a role in cytoplasmic trafficking of mercury (Ettema et al, 2003). This role was subsequently confirmed through experimental studies (Schelert et al, 2013). Finally, the S. solfataricus MerR transcription factor regulates merHAI transcription in a metal-dependent fashion.…”

“…Growth was monitored by measuring the OD 540 and growth curves were plotted. To determine the intracellular concentration of mercury, inductively coupled plasma (ICP)-MS analysis was carried out as described previously (Schelert et al, 2013). Mercury-treated cells corresponding to *10 8 cells ml 21 were then removed at the indicated times and cells were harvested by centrifugation at 10 000 g for 5 min followed by two successive washes using distilled water to remove free mercury.…”

Secretion and fusion of biogeochemically active archaeal membrane vesicles

“…Samples (300 μl) were removed every day to evaluate copper solubilization, filtered using 0.45 μm membranes and stored at 4°C until analyzed. Solublilized copper was determined by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), as described elsewhere (Maezato et al, 2012;Schelert, Rudrappa, Johnson, & Blum, 2013). Biological triplicates and technical triplicates were used to derive mean and standard deviation values.…”

Expanding the Limits of Thermoacidophily in the Archaeon Sulfolobus solfataricus by Adaptive Evolution

“…These are both SirA response regulators, two-component response regulators that control secondary metabolism and have a signature CPxP motif that might be important in mRNA binding (54). In addition, the MerI protein, SULA_0494, which contains a CBS domain implicated in ionic sensing (55) and energy status sensing (56), was also upregulated in SULC along with the entire mercury resistance operon (mer), which encodes MerH (mercury chaperone) and MerA (mercuric reductase) (28,29,57). Induction of the mer operon suggests that growth at lower pH is an oxidative stress, as recent studies demonstrated that the MerR transcription factor also controls the expression of MarR, an oxidative stress regulator (58).…”