Exploiting the arsenic resistance of the thermophilic bacterium Thermus thermophilus

Introduction Microorganisms living in arsenic-rich geothermal environments act on arsenic using different biochemical strategies. So far, only limited insights have been obtained on the molecular mechanisms responsible for the arsenic resistance [1]. Investigation on the thermophilic bacterium Thermus thermophilus HB27 highlighted its tolerance to millimolar concentrations of As(V) and As(III). In fact, its genome encodes for an arsenate reductase, which is an important contributor in the arsenic resistance system [2]. In this study we focused on the role of the putative transcriptional regulator TtSmtB (TTC0353), belonging to ArsR/SmtB family, by in vivo and in vitro analysis. Methods A RT-PCR analysis was performed to identify TtSmtB transcriptional unit where putative internal promoters were found. TtSmtB was cloned in pET28b, expressed and the recombinant protein purified and characterized by EMSA assays for its ability to bind putative target promoters. A T. thermophilus TtsmtB- knocked strain was generated and characterized by qRT-PCR on putative TtSmtB target genes. Results TtSmtB gene is part of an operon of five genes not metabolically related with three arsenic responsive promoters upstream of TTC0351, TTC0353 and TTC0354. The recombinant protein is a dimer interacting with the target promoters. qRT-PCR on TtSmtB, TTC0351 and TTC0354 in the wild type showed an increased expression in the presence of arsenic. Furthermore, their expression in the knocked strain was always greater than in the wild type. Conclusions Our result show that TtSmtB is able to sense arsenic and acts as a transcriptional repressor of the entire operon in which it is encoded. 1) D. Páez-Espino, et al. 2009 Biometals, 22:117–130 2) Del Giudice I et al. 2013 Biochim Biophys Acta, 1834:2071-9