Papers in the Biological Sciences


Date of this Version



Microbiology (2013), 159, 1198–1208


Copyright 2013 SGM


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.

Included in

Biology Commons