MroQ is a Novel Abi-domain Protein That Influences Virulence Gene Expression in Staphylococcus aureus via Modulation of Agr Activity

Numerous factors have to date been identified as playing a role in the regulation of Agr activity in S. aureus, including transcription factors, antisense RNAs, and host elements. Herein we investigate the product of SAUSA300_1984 (termed MroQ), a transmembrane Abi-domain/M79 protease-family protein, as a novel effector of this system. Using a USA300 mroQ mutant we observed a drastic reduction in proteolysis, hemolysis and pigmentation that was fully complementable. This appears to result from diminished agr activity, as transcriptional analysis revealed significant decreases in expression of both RNAII and RNAIII in the mroQ mutant. Such effects appear to be direct, rather than indirect, as known agr effectors demonstrated limited alterations in their activity upon mroQ disruption. A comparison of RNA-sequencing datasets for both mroQ and agr mutants reveal a profound overlap in their regulomes, with the majority of factors affected being known virulence determinants. Importantly, the preponderance of alterations in expression were more striking in the agr mutant, indicating that MroQ is necessary, but not sufficient, for Agr function. Mechanism profiling revealed that putative residues for metalloprotease activity within MroQ are required for its Agr controlling effect, however this is not wielded at the level of AgrD processing. Virulence assessment demonstrated that mroQ and agr mutants both exhibited increased formation of renal abscesses, but decreased skin abscess formation, alongside diminished dermonecrosis. Collectively, we present the characterization of a novel agr effector in S. aureus, which would appear to be a direct regulator, potentially functioning via interaction with the AgrC histidine kinase.