Date of Award

Fall 12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Committee Chair

Mohamed O. Elasri

Committee Chair Department

Biological Sciences

Committee Member 2

Shahid Karim

Committee Member 2 Department

Biological Sciences

Committee Member 3

Glenmore Shearer

Committee Member 3 Department

Biological Sciences

Committee Member 4

Yanglin Guo

Committee Member 4 Department

Biological Sciences

Committee Member 5

Fengwei Bai

Committee Member 5 Department

Biological Sciences

Abstract

Community-acquired, methicillin-resistant Staphylococcus aureus strains often cause localized infections in immune-compromised hosts, but some strains show enhanced virulence leading to severe infections even among healthy individuals with no predisposing risk factors. The genetic basis for this enhanced virulence has yet to be determined. S. aureus possesses a wide variety of virulence factors, the expression of which is carefully coordinated by a variety of regulators. Several virulence regulators have been well characterized, but others have yet to be thoroughly investigated. Previously, the msa gene as a regulator of several virulence genes, biofilm development, and antibiotic resistance was identified. The evidence of the involvement of upstream genes in msa function was also observed. To investigate the mechanism of regulation of the msa gene (renamed msaC), the upstream genes whose expression was affected by its deletion was studied. Further study showed that msaC is part of a newly defined four- gene operon (msaABCR), in which msaC is a non-protein-coding RNA that is essential for the function of the operon. Furthermore, the study also found an antisense RNA (msaR) is complementary to the 5’ end of the msaB gene and is expressed in a growth phase-dependent manner suggesting that it is involved in regulation of the operon.

One of the most important aspects of staphylococcal infections is biofilm development within the host, which renders them resistant to the immune response and antimicrobial agents. Biofilm development is very complex and involves several regulators that ensure cell survival on surfaces within the extrapolymeric matrix. In this study, the regulatory pathway that msaABCR uses to control biofilm formation was identified. This study showed that the msaABCR operon is a negative regulator of proteases. Control of protease production mediates processing of the major autolysin Atl and therefore regulates rates of autolysis. In the absence of the msaABCR operon, Atl is processed by proteases at a high rate, which leads to increased cell death and a defect in biofilm maturation. This study also found that the msaABCR operon plays a key role in maintaining the balance between autolysis and growth within staphylococcal biofilm.

These findings will allow defining a new operon that regulates fundamental phenotypes in S. aureus such as biofilm development and virulence. Characterization of the msaABCR operon will allow the investigation of the mechanism of function of this operon and the role of the individual genes in regulation and interaction with its targets. This study identifies a new element in the complex regulatory circuits in S. aureus, and the findings may be therapeutically relevant.

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