MroQ Is a Novel Abi-Domain Protein That Influences Virulence Gene Expression in <i>Staphylococcus aureus</i> via Modulation of Agr Activity

Abstract

Numerous factors have, to date, been identified as playing a role in the regulation of Agr activity in <i>Staphylococcus aureus</i>, including transcription factors, antisense RNAs, and host elements. Herein we investigated 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 <i>mroQ</i> mutant, we observed a drastic reduction in proteolysis, hemolysis, and pigmentation that was fully complementable. This appears to result from diminished <i>agr</i> activity, as transcriptional analysis revealed significant decreases in expression of both RNAII and RNAIII in the <i>mroQ</i> mutant. Such effects appear to be direct, rather than indirect, as known <i>agr</i> effectors demonstrated limited alterations in their activity upon <i>mroQ</i> disruption. A comparison of RNA sequencing data sets for both <i>mroQ</i> and <i>agr</i> mutants revealed 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 <i>agr</i> 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 was not wielded at the level of AgrD processing. Virulence assessment demonstrated that both <i>mroQ</i> and <i>agr</i> mutants exhibited increased formation of renal abscesses but decreased skin abscess formation alongside diminished dermonecrosis. Collectively, we present the characterization of a novel <i>agr</i> effector in <i>S. aureus</i> which would appear to be a direct regulator, potentially functioning via interaction with the AgrC histidine kinase.