The Q225P Mutation in SigB Promotes Membrane Vesicle Formation in Staphylococcus aureus

Both Gram-positive and Gram-negative bacteria release nano-sized lipid bilayered particles, known as membrane vesicles (MVs), into external environments. Although MVs play a variety of roles in bacterial physiology and pathogenesis, the mechanisms underlying MV formation in Gram-positive microorganisms such as Staphylococcus aureus remain obscure. Bacterial MV production can be induced in response to stress conditions, and the alternative sigma factor B (SigB) functions as a central regulator of the stress response in Gram-positive bacteria. In a previous study, we demonstrated that the SigB(Q225P) substitution mutation in S. aureus promotes biofilm formation. Here, we report that the SigB(Q225P) mutation also increases MV production in this important pathogen. LacZ reporter assays and electrophoretic mobility shift assays showed that the Q225P substitution reduces SigB binding to the promoter region of the thermonuclease gene (nuc), resulting in a significant reduction in Nuc expression. Deletion of nuc markedly enhances S. aureus MV generation, possibly due to the accumulation of nucleic acids. These results are not only important for understanding MV biogenesis in S. aureus, but also useful for the development of a S. aureus MV-based platform for MV application.