Role of Alarmones in The Protection of Escherichia coli Against Stress

Escherichia coli has evolved in environments which may commonly be acidic and thus developed adaptive mechanisms to minimise acid-induced damage. It has previously been observed that adapted bacteria to moderately acidic conditions can grow in media considerably below their optimum growth pH. To explain this phenomenon, a hypothesis which suggested that diffusible molecules (alarmones) may serve as early warning systems of acidic conditions was proposed. Alarmones are thought to be produced upon exposure to mildly-acidic conditions. They then diffuse in the environment and elicit a protective response against acid in recipient cells. The protective activity of those putative alarmones against lethal acid was investigated. The main aim of this project is to determine the mode of action of those alarmones at the molecular level. Preliminary experiments confirmed acid resistance conferred by alarmones to populations of E. coli C600. The stability of those alarmones at different temperatures and following proteinase K treatment was investigated. Moreover, investigations into whether alarmones are autoinducer-2 (AI-2) molecules and whether alarmones increase the percentage of persisters in an E. coli population were undertaken. Subsequently, microarray analyses of both alarmone-induced and non-induced cultures were performed to reveal E. coli genes induced by alarmones. Moreover, proteomic studies using two-dimensional gel electrophoresis were conducted to reveal proteins induced by alarmones. Supernatants from alarmone-induced cultures conferred statistically significant protection (p