CztR, a LysR-Type Transcriptional Regulator Involved in Zinc Homeostasis and Oxidative Stress Defense in Caulobacter crescentus

Abstract

Caulobacter crescentus is a free-living alphaproteobacterium that has 11 predicted LysR-type transcriptional regulators (LTTRs). Previously, a C. crescentus mutant strain with a mini-Tn5lacZ transposon inserted into a gene encoding an LTTR was isolated; this mutant was sensitive to cadmium. In this work, a mutant strain with a deletion was obtained, and the role of this LTTR (called CztR here) was evaluated. The transcriptional start site of this gene was determined by primer extension analysis, and its promoter was cloned in front of a lacZ reporter gene. ␤-Galactosidase activity assays, performed with the wild-type and mutant strains, indicated that this gene is 2-fold induced when cells enter stationary phase and that it is negatively autoregulated. Moreover, this regulator is essential for the expression of the divergent cztA gene at stationary phase, in minimal medium, and in response to zinc depletion. This gene encodes a hypothetical protein containing 10 predicted transmembrane segments, and its expression pattern suggests that it encodes a putative zinc transporter. The cztR strain was also shown to be sensitive to superoxide (generated by paraquat) and to hydrogen peroxide but not to tert-butyl hydroperoxide. The expression of katG and ahpC, but not that of the superoxide dismutase genes, was increased in the cztR mutant. A model is proposed to explain how CztR binding to the divergent regulatory regions could activate cztA expression and repress its own transcription.

Transposon Mutagenesis Paired with Deep Sequencing of Caulobacter crescentus under Uranium Stress Reveals Genes Essential for Detoxification and Stress Tolerance

“…Braz et al found that CztR autoregulates its own expression and positively regulates expression of CztA, demonstrating a link between these two proteins (51). They propose that the CztRA system is involved in zinc transport under zinc-limited conditions and that CztR may be involved in regulation of other oxidative stress genes (51). We found that a cztR mutant, but not a cztA mutant, is more susceptible to U in terms of both growth and survival, suggesting that CztR does not confer U resistance by activating expression of cztA.…”

“…Although the CztRA system may not be specifically induced by U, it clearly plays a role in U fitness under both survival and growth conditions. Given its previously reported function in Cd resistance (35,51), the CztRA system may be involved in a general heavy metal stress response.…”

“…The cztR and cztA genes were also significant hits in our Tn-seq screen. The cztR gene encodes a LysR family transcriptional regulator that, along with the putative CztA transporter, has been implicated in response to Zn limitation and Cd exposure (51). To characterize the contribution of CztRA to U tolerance, we performed growth and survival assays in strains lacking cztR or cztA.…”

Contribution of GO System Glycosylases to Mutation Prevention in Caulobacter crescentus

“…Escherichia coli shows a slightly higher (1.5-fold) basal level of 8-oxodGuo in DNA than C. crescentus, but this difference is not statistically significant. Caulobacter crescentus has a myriad of regulons that promote resistance to oxidative stress (Alvarez-Martinez et al 2007;Da Silva Neto et al 2009;Lourenço and Gomes 2009;Braz et al 2010;Foreman et al 2012), and perhaps is more protected from endogenous sources of ROS, leading to lower levels of oxidative damage. Caulobacter crescentus has a myriad of regulons that promote resistance to oxidative stress (Alvarez-Martinez et al 2007;Da Silva Neto et al 2009;Lourenço and Gomes 2009;Braz et al 2010;Foreman et al 2012), and perhaps is more protected from endogenous sources of ROS, leading to lower levels of oxidative damage.…”

A Non-Classical LysR-Type Transcriptional Regulator PA2206 Is Required for an Effective Oxidative Stress Response in Pseudomonas aeruginosa

“…In Escherichia coli , OxyR works in concert with the small RNA oxyS to coordinate expression of catalase and peroxidase genes [3]. More recently, several other LTTRs have been shown to play a role in the oxidative stress response, including Hrg in Salmonella enterica [4], HypR in Enterococcus faecalis [5], CztR in Caulobacter crescentus [6] and HcaR in E. coli [7]. However, with the exception of OxyR, the role of LTTRs during oxidative stress remains largely uncharacterised in many bacteria.…”