- Title
- Metabolomic and proteomic responses of Staphylococcus aureus to changes in the environmental conditions
- Creator
- Alreshidi, Mousa
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Staphylococcus aureus is the causative agent of a high number of acute and chronic diseases. The ability of this bacterium to cause disease can be attributed to a massive range of virulence factors to facilitate penetration and invasion of host tissues. It is also likely that its success as a pathogen can be partly attributed to the remarkable ability to rapidly adapt to multiple and continuous changes in the environment including temperature, pH and osmotic pressure. The acclimation of this bacterium was thought to occur through a wide range of processes including alterations in metabolic and proteomic profiles. These alterations in metabolic profiles and proteomic composition were proposed to lead to the generation of new phenotypes. These phenotypes, e.g. small colony variants, were found to be more resilient and represent a survival strategy used by some bacteria, including staphylococci species to withstand alterations in environmental conditions. The primary aim of this thesis was to study the adjustments that occur in cytoplasmic metabolites and proteins in S. aureus in response to environmental stresses. Bacterial cells from the same stock culture were exposed a range of environmental conditions for comparison of the cytoplasmic metabolite and protein compositions to determine whether measurable and differential adaptive mechanisms could be determined. It was hypothesised that S. aureus would adjust its metabolic profiles and protein composition to facilitate survival under the growth conditions tested. The first study harvested cells at the mid exponential phase of growth under ideal conditions at 37ºC for comparison with equivalent sets of cells which were exposed to prolonged cold stress for 2 weeks at 4 °C. Principle component analysis (PCA) of the metabolomic and proteomic data indicated that the prolonged exposures to cold stress conditions generated cells with different metabolite and protein profiles compared with corresponding cells harvested at the mid-exponential phase of growth. All replicate samples from the prolonged cold treatment were tightly clustered and well resolved from the control reference samples. The ribosomal proteins S1, S7, S8, L3, L5, L10, L17, L24, L25, and L30 and citric acid were substantially elevated in the cytoplasmic fractions from the cells adapted to cold-stress but most amino acids showed a reduction in their concentration in cold-stressed samples. This study provided strong evidence supporting the hypothesis that specific changes in metabolic homeostasis and protein composition were essential for acclimatized processes necessarily for empowering survival in response to prolonged cold stress. The response of S. aureus to multiple combination of environmental conditions to mimic those on the human skin or within a wound site: pH6-8, temperature 35-37 °C, and 0-5% NaCl added, was also investigated. Cultures grown under optimal conditions at 37°C and pH7 with no additional NaCl were designated as the reference control samples. It was hypothesised that S. aureus cells grown under different sets would have adapted their metabolic homeostasis in a manner unique to each of the specific sets of conditions. This study was conducted to assess the bacterial responses to subtle changes in the environment by measuring levels of cytoplasmic amino acids and ribosomal proteins. It was found that each set of environmental conditions elicited substantial adjustments in cytoplasmic levels of glutamic acid, aspartic acid, proline, alanine and glycine (P< 0.05) which generated characteristic amino acid profiles. Substantial alterations in cytoplasmic amino acid and protein composition occurred during growth under conditions of higher osmotic pressure implemented via additional levels of NaCl in the growth medium. The cells responded to additional NaCl at pH 6 by reducing levels of ribosomal proteins, whereas at pH 8 there was an upregulation of most of the ribosomal proteins compared with ribosomal protein L10, did not increase in the two treatments that resulted in a general increase in the other ribosomal proteins. L9 was the only ribosomal protein that was reduced in cytoplasmic concentration in both treatments where there was no general ribosomal response. L32 was the only ribosomal protein that did not change in cytoplasmic concentrations across all experiments growth at ideal control conditions. The data supported the hypothesis that the bacterium was continually responding to the dynamic environment by modifying the proteome and optimising metabolic homeostasis. Metabolomic and secreteomic comparison between a clinical isolate and ATCC 29213 strain of S. aureus was also examined in this thesis. The clinical and typed strains had different sets of metabolic homeostasis under control conditions at the mid-exponential and stationary phases of growth. In addition, clinical and typed strains altered characteristically in regard to their metabolic profiles for each of the corresponding sets of environmental conditions. Secreteomic analysis of the examined strains also revealed that each strain secreted unique secreteomic profiles when either grown under ideal conditions or changed environmental conditions. It was concluded that the changes in metabolites and proteins were essential as an adaptation process for responding to changes in environmental conditions. The main outcomes found in this thesis were that ribosomal proteins and amino acids undergo significant alterations in response to prolonged cold stress or subtle and combined alterations in environmental conditions. It was concluded that specific protein and amino acid adjustments would provide the basis for the adaptive mechanisms that have led to the evolutionary survival and optimal conditioning of S. aureus to take advantage of prevailing conditions and infective opportunities.
- Subject
- <i>S. aureus</i>; proteomic; metabolomic; phenomics
- Identifier
- http://hdl.handle.net/1959.13/1312609
- Identifier
- uon:22441
- Rights
- Copyright 2016 Mousa Alreshidi
- Language
- eng
- Full Text
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