The complex regulation of competence in Staphylococcus aureus under microaerobic conditions

To perform natural transformation, one of the three main Horizontal Gene Transfer mechanisms, bacteria need to enter a physiological differentiated state called genetic competence. Interestingly, new bacteria displaying such aptitude are often discovered, and one of the latest is the human pathogen Staphylococcus aureus. Here, we show an optimized protocol, based on planktonic cells cultures, leading to a large percentage of the population activating the development of competence and a significant improvement of S. aureus natural transformation efficiencies. Taking advantage of these conditions, we perform transcriptomics analyses to characterize the regulon of each central competence regulator. SigH and ComK1 are both found essential for activating natural transformation genes but also important for activation or repression of peripheral functions. Even though ComK2 is not found important for the control of transformation genes, its regulon shows an important overlap with that of SigH and ComK1. Finally, we propose that microaerobic conditions, sensed by the SrrAB two-component system, are key to activate competence in S. aureus.