Year: 2015
Type: dissertation
Abstract: Proteins and enzymes require metal ions as enzymatic cofactors for optimal biological activities. Copper metal ion is utilized by various bacterial systems in trace amounts; however, it can be extremely toxic at higher concentrations. The copYABZ operon, involved in copper homeostasis, has been extensively studied and characterized in several Gram positive bacteria. CopA and CopB encode for P-type ATPases, involved in copper translocation, whereas, CopY and CopZ regulate the expression of the cop operon. In Streptococcus mutans, the primary etiological agent of dental caries, copYAZ has been partially investigated for its role in copper transport and resistance. In this study, we demonstrated the probable mechanisms by which copper induces toxicity in S. mutans; and elucidated the role of copYAZ operon in modulating copper transport and resistance, as well as other physiological processes of this oral pathogen. Copper induces toxicity by generating oxidative stress and dissipating membrane potential in S. mutans. During biofilm growth, copper impaired S. mutans ability to adhere to a surface and produce biofilm biomass; while significantly repressing the expression of genes involved in maintaining the functional and structural integrity of biofilm matrix. Results from copper transport studies validated the role of copYAZ in copper efflux in S. mutans. The knock-out strain in copYAZ (∆copYAZ) was more sensitive to copper, oxidative and acid stress relative to its wild type. Loss of copYAZ resulted in prolonged membrane depolarization in S. mutans. The presence of copper and/or the absence of copYAZ significantly impaired S. mutans ability to acquire foreign DNA from the surrounding environments; while repressing the transcription of genes involved in competence development. The copYAZ-associated phenotypes were further validated via genetic complementation studies. Taken collectively, we illustrated the implications of copper-induced toxicity in S. mutans; and have provided evidence describing the importance of copYAZ operon in copper resistance and transport, biofilm formation, acid and oxidative stress tolerance, maintenance of membrane potential, and genetic transformation in S. mutans.
Source: TSpace (University of Toronto)
Author: Kamna Singh
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2562784191