aureus clpX, clpC, clpB, clpL, ATP-dependent chaperones, which affected virulence in animal models, biofilm formation, endocytosis,

cell wall autolysis, and resistance to stress exposure [16–18]. These genetic studies demonstrated the complex molecular interactions of stress response mechanisms, occurring at both transcriptional and post-translational levels [15–18]. While clpC, clpB, PLX-4720 and clpP are controlled by the CtsR repressor, the HrCA regulon (dnaK and groESL operons) of S. aureus was found embedded within the CtsR regulon, in contrast to B. subtilis, which might provide a tighter control of major heat shock regulons in S. aureus [13, 19]. Initially considered as a major stress response system that would help to face diverse stressful stimuli (including some antibiotics) [20, 21], the SigB regulon is now believed to have a more general physiological impact on S. aureus compared to B. subtilis or E. coli, influencing ca. 200 genes involved in several cellular processes such as cell envelope composition, membrane transport processes, and intermediary metabolism [22, 23]. The SigB operon of S. aureus is composed of four ORFs (rsbU, rsbV, rsbW, sigB), coding for the regulatory network components

of transcriptional factor sigma B activity (SigB) [20, 21, 24, 25]. Evaluation of intracellular levels and functional activity of free SigB is achieved by assaying transcription of the SigB-dependent target gene asp23 [26]. Previous studies have shown that S. aureus strain NCTC8325 and its in vitro-generated derivatives are defective in RsbU expression thus impairing Lumacaftor supplier post-transcriptional, upregulation of free SigB

by external or internal stimuli [27–29]. In the past decades, S. aureus responses to heat shock exposure were evaluated by a variety of molecular and physiological assays, which yielded a still fragmentary view of the mechanisms determining bacterial survival or death at supra-physiological temperatures [14, 30–33]. This report aims to analyze diverse facets Vitamin B12 of S. aureus stress responses to heat exposure, by evaluating in parallel the combined action of specific stress response mechanisms with more general, energy-regulating metabolic pathways. The short term physiological adjustment of S. aureus from 37°C to higher temperatures was evaluated by recording the global transcriptomic responses of bacterial cultures briefly exposed (10 min) to one sub-lethal (43°C) and one eventually lethal (48°C) temperature, in parallel with determination of some major intracellular and extracellular markers of metabolic pathways regulating energy sources and microbial cell viability. Results and discussion Global analysis of transcriptomic responses To evaluate the impact of temperature up-shifts on the transcriptomic profile of S. aureus ISP794, we sorted all genes whose transcript levels were ≥ 2-fold upregulated or down-regulated by 10-min up-shifts from 37°C to 43°C or 48°C.