Redox Regulation and Stress Responses - Studies in Bacillus subtilis

University dissertation from Cell and Organism Biology Lund University Sölvegatan 35 SE-22362 Lund

Abstract: Redox reactions are central to all organisms to sustain life. Both anabolic and catabolic metabolism depends on them. It is thus vital to sense and adjust the redox balance in the cell. One major factor affecting the redox status is the level of oxygen present. Transitions between different oxygen concentrations change the redox status and among other things, confer a stress upon the cells. This stress ultimately leads to altered expression levels of genes necessary to cope with the new conditions. In this thesis different aspects of what ultimately causes stressful situations, and what bacteria can do to counteract them are analysed. The redox-sensing protein Rex (YdiH) from Bacillus subtilis is characterised. Rex adjusts the cell in a way that enables conservation of energy by means other than aerobic respiration. This is accomplished by coordinating the regulation of three systems involved in growth at low oxygen levels. Exposure of cells to damaging nitrogen compounds exerts a stress upon the bacteria. This work shows that the cellular response involves two systems. One is an inducible system (hmp) involving a haemoglobin-like protein for direct detoxification of the nitrogen compounds, while the other system confers a constitutive protection (yjbIH). The thesis also describes a hitherto uncharacterised protein (YjbH), which has a key role in the control of the global regulator Spx, which in turn is involved in disulphide stress management.

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