Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Nanduri, Bindu

Committee Member

Thornton, Justin

Committee Member

Swiatlo, Edwin

Committee Member

Perkins, Andy

Date of Degree

8-6-2021

Original embargo terms

Visible to MSU only for 2 years

Document Type

Dissertation - Open Access

Major

Veterinary Sciences (Infectious diseases)

Degree Name

Doctor of Philosophy

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Veterinary Medicine

College

College of Veterinary Medicine

Department

Department of Comparative Biomedical Sciences

Department

Department of Comparative Biomedical Sciences

Abstract

This dissertation is a compilation of published work and a manuscript that seeks to understand the role of polyamine metabolism in the regulation of pneumococcal physiology. Streptococcus pneumoniae (pneumococcus) is the major cause of community-acquired pneumonia, and otitis media worldwide. Genetic diversity and serotype replacement, and antibiotics resistance to confound existing therapeutic strategies and limit the effectiveness of the available capsule polysaccharide (CPS) based vaccines. Polyamines such as putrescine, spermidine and cadaverine are ubiquitous polycationic hydrocarbons that interact with negatively charged molecules and modulate important cellular processes. Intracellular polyamine concentrations are regulated by biosynthesis, degradation, and transport. This work investigated the impact of the deletion of polyamine biosynthesis gene, SP_0916 (cadA, lysine/arginine decarboxylase covered in the second, third and fourth chapters), on growth, Gram staining characteristics, capsule production, proteome and stress responses of virulent pneumococcal serotype 4 (TIGR4). We identified loss of capsular polysaccharide (CPS) in DELTA SP_0916 strain. Our proteome results showed a shift in metabolism towards the pentose phosphate pathway (PPP) that could reduce the availability of precursors for CPS and could explain the un-encapsulated phenotype of DELTA SP_0916. Since a shift towards the PPP is usually in response to stress, we compared the stress responses of DELTA SP_0916 to that of TIGR4. Our results show that the mutant was more susceptible to oxidative, nitrosative, and acid stress compared to the wild type. In the fifth chapter we compared the transcriptome, metabolome, stress responses and stress susceptibility of the polyamine transport deficient strain (DELTA potABCD) and S. pneumoniae TIGR4. Results in this chapter show that polyamine transport is essential for pneumococcal stress responses, and capsule biosynthesis. The impact of impaired polyamine synthesis (DELTA SP_0916), and transport (DELTA potABCD) on pneumococcal capsule is due to altered expression of Leloir pathway, reduced glycolysis, and increased PPP, possibly in response to impaired stress responses. These results demonstrate that alteration of polyamine pathways affects pneumococcal stress responses which in turn could limit the availability of precursors for capsule synthesis, and thus have an impact on virulence. Thus, polyamine metabolism is an attractive avenue for developing novel interventions for limiting the spread of S. pneumoniae, a versatile human pathogen.

Sponsorship

The Center for Biomedical Research Excellence in Pathogen Host Interactions, National Institute for General Medical Sciences (grant no. P20GM103646).

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