Date of Award

Summer 8-2021

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological, Environmental, and Earth Sciences

Committee Chair

Dr. Mohamed O. Elasri

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Dr. Janet Donaldson

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Dr. Alex Flynt

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Committee Member 4

Dr. Fengwei Bai

Committee Member 4 School

Biological, Environmental, and Earth Sciences

Committee Member 5

Dr. Jacques Kessl

Committee Member 5 School

Mathematics and Natural Sciences


Staphylococcus aureus is an important human pathogen in both community and health care settings. Biggest challenges with S. aureus as a pathogen is its ability to acquire antibiotic resistance and produce robust biofilms. In this work, we investigated the nature of the cell wall defect in the msaABCR operon mutant in the Mu50 (VISA) and USA300 LAC methicillin-resistant Staphylococcus aureus (MRSA) strains. Results showed that msaABCR-mutant cells had decreased cell wall thickness and cell wall crosslinking in both strains. These defects are most likely due to increased murein hydrolase activity and/or nonspecific processing of murein hydrolases mediated by increased protease activity in mutant cells. The defect was enhanced by a decrease in teichoic acid content in the msaABCR mutant cell wall. Moreover, we also observed significantly downregulated transcription of early cell wall-synthesizing genes, supporting the finding that msaABCR-mutant cells have decreased peptidoglycan synthesis. Thus, we conclude that the msaABCR operon controls the balance between cell wall synthesis and cell wall hydrolysis, which is required for maintaining a robust cell wall and acquiring resistance to cell wall-targeting antibiotics, such as vancomycin and the β-lactams.

This dissertation also elucidated the mechanism of the cell death phenomenon regulated by the msaABCR operon at the molecular level in the USA300 LAC strain. This study showed that msaABCR represses weak acid-dependent cell death. Rate of glucose consumption, and acetate and acetoin production in msaABCR mutant was higher than the USA300 LAC (wild type) strain in the biofilm microenvironment, which caused increased intracellular acidification and led to increased cell death. We showed that MsaB binds directly to the LysR-type transcriptional regulator, cidR promoter and represses expression of the cidR regulon. We also showed role of MsaB in indirect repression of pyruvate catabolism via cidR to play an important role in overflow metabolism and programmed cell death during biofilm development in S. aureus. In addition, pyruvate was also shown to induce expression of the msaABCR operon. This article has thus deciphered the role of the msaABCR operon in staphylococcal metabolic adaption during biofilm development.