Date of Award

2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Gram-positive bacteria produce small autoinducing peptides (AIPs), which act to regulate expression of genes that promote adaptive traits including virulence. The Gram-positive pathogen Staphylococcus aureus generates a cyclic AIP that controls expression of virulence factors via the accessory gene regulatory (Agr) system. S. aureus strains belong to one of four Agr groups (I, II, III, and IV), and each group harbors allelic variants of AgrD, the precursor of AIP. In a prior screen for S. aureus virulence factors, the Alonzo lab identified MroQ, a putative peptidase. A ΔmroQ mutant closely resembled a Δagr mutant and had significant defects in AIP production in an Agr-I strain. I show that expression of AgrD-I in a ΔmroQ mutant leads to accumulation of an AIP processing intermediate at the membrane that coincides with a loss of secreted mature AIP, indicating MroQ promotes maturation of AgrD-I. MroQ is conserved in all Agr sequence variants, suggesting either identical function amongst all Agr types or activity specific to Agr-I strains. My data indicate that MroQ is required for AIP maturation and activity in Agr-I, -II, and -IV strains irrespective of background. However, MroQ is not required for Agr-III activity despite an identifiable role in peptide maturation. My work suggests that these results may be due to the ability of an AIP-III intermediate to serve as an active AIP. Isogenic Δagr and Δagr ΔmroQ strains complemented with Agr-I-IV validated the critical role for MroQ in the generation of active AIP-I, -II, and -IV, but not AIP-III. These findings were reinforced by skin infection studies in mice. Exploration of other Gram-positive bacteria identified MroQ homologues which may also contribute to respective Agr system function. Together, my data substantiate the prevailing model that MroQ is a mediator of cyclic peptide maturation and highlight a role for Type II CAAX proteases in Gram-positive bacteria.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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