Survival of Escherichia coli has been examined under the effect of various environmental factors, nutrient and stress conditions in natural lake water or sterile microcosms. E.coli could survive for at least 200 days at temperatures below 25 °C under starvation stress in sterile lake water. Whilst E.coli survived for the longest period of time at 4°C, the shortest survival time was always at 37°C in both natural and sterile lake water microcosms. Predation by protozoa was not found to be a significant factor affecting the survival of E.coli in natural lake water microcosms. The addition of sources of nutrients to lake water enhanced the survival of E.coli in both natural and sterile lake water. E.coli could grow in the lake water with the addition of a single carbon source or single amino acid addition but ultimately there was an accelerated decline in numbers. On the other hand the addition of ammonium sulphate and casein enhanced survival and allowed growth. The measurement of metabolic enzyme activities such as succinate and NADH dehydrogenase activity showed that E.coli reduced its metabolic activity very quickly upon starvation especially at 37°C. The reduction in activity was again temperature dependent. E.coli cells also reduced in size under starvation stress in lake water and the rate at the size reduced was temperature dependent. Measurements of the respiratory activity of the cells showed that although the viable count declined below detection limits under starvation stress, at least 50% of the cells could still respire. This indicates that the cells enter a viable but non-culturable phase in lake water. Alkaline phosphatase activity increased in cells which were incubated under starvation conditions. Pretreatment of the cells with alcohol, hydrogen peroxide or salt to induce stress proteins also lead to an increase in alkaline phosphatase activity. The addition of nutrient sources, particularly amino acids, to sterile lake water microcosms increased the activity of alkaline phosphatase and fi-galactosidase enzymes Two-dimensional gel electrophoresis was used to show changes in the protein patterns of E.coli affected by starvation and other stress conditions. Some proteins were induced under starvation conditions, others were repressed. The changes in the relative concentration of the outer membrane proteins, OmpC, OmpF and OmpA were quantified. All were affected by starvation stress with OmpA disappearing from the outer membrane. A 45 kDa protein was induced under all stress conditions. Other stresses resulted in the induction of a 70 kDa protein (oxidation stress by hydrogen peroxide) or the complete disappearance of the major outer membrane proteins (sodium dodecyl sulphate treatment). The survival of E.coli under starvation and other stress conditions was correlated with the induction of specific proteins.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:238770 |
| Date | January 1993 |
| Creators | Ozkanca, Resit |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/103888/ |
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