SigmaB regulates ccrAB expression and SCCmec excision in methicillin-resistant Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a global health threat due to its resistance to beta-lactam antibiotics.
• This resistance is conferred by the mecA gene, located on the staphylococcal cassette chromosome mec (SCCmec) mobile element.
• The excision and integration of SCCmec are regulated by Ccr recombinases (ccrAB or ccrC), but the control mechanisms for ccrAB gene expression remain unclear.

Purpose of the Study:

• To investigate the molecular mechanisms controlling ccrAB gene expression and SCCmec mobility in MRSA.
• To elucidate the role of alternative sigma factors, specifically SigB, in regulating SCCmec dynamics.

Main Methods:

• Overexpression of SigB in MRSA strain N315.
• Analysis of ccrA transcription and SCCmec excision.
• Primer extension-blot analysis and 5'RACE (Rapid Amplification of cDNA Ends) to identify promoter regions.

Main Results:

• Overexpression of SigB significantly enhanced ccrA transcription and SCCmec excision in MRSA.
• Identification of a novel SigB-dependent promoter within SCCmec types II and IV.
• ccrAB genes are transcribed via a two-promoter system, with the SigB-dependent promoter showing low activity under normal conditions.

Conclusions:

• SigB plays a crucial role in regulating SCCmec excision and transfer in MRSA.
• The newly identified SigB-dependent promoter is responsible for enhanced ccrA transcription and SCCmec mobility.
• Understanding SigB's role provides insights into the horizontal gene transfer of antibiotic resistance genes.