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Bacteria are able to colonize a large quantity of different environments. These habitats underlie extensive variations of biotic and abiotic factors to which the bacterial cell has to respond timely to ensure growth and survival. The habitat of the gram-positive bacterium Bacillus subtilis is the upper layers of the soil and the rizosphere. Here two of the most important abiotic factors are directly influencing the bacterial cell. B. subtilis is due to alteration of day and night, weather conditions and changing seasons, exposed to constant variations in osmolarity and temperature. DNA-array analysis of B. subtilis have shown, that there are a lot of genes involved in cell wall metabolism which are induced by hyperosmotic conditions and adaptive growth at 15°C (Steil et al., 2003, Budde et al., 2006). This is a hint, that the proteins coded by these genes play important roles in the adaptation of cell wall structure and composition of B. subtilis under stress conditions. In regard to that, it could be shown before for several bacterial species that the cell envelope and especially the cell wall is changing upon increase in osmolarity and a drop in temperature (Vijaranakul et al., 1995, Lopez et al., 1998, Lopez et al., 2000, Piuri et al., 2005, Palomino et al., 2008).
One of the genes which could be identified as induced by osmotic- and cold stress in B. subtilis is the yocH gene.
In the present dissertation the genetic regulation of the yocH gene and the function of the YocH protein could be characterised in detail. Due to biochemical analysis of the purified YocH protein and an analysis of a YocH-GFP fusion it could be shown, that YocH is a peptidoglycan associated cell wall hydrolase. YocH has an important role in the dynamic reconstruction of the peptidoglycan during growth under stress condtions, as a yocH deletion mutant is sensitive to high osmolarity. The expression of the yocH gene is controlled be the single essential two-component regulatory system (YycFG) of B. subtilis (Howell et al., 2003; Dubrac et al., 2008).
The presented data gain a first insight into the architecture of the regulatory region of yocH and the transcriptional regulation of this gene responding to hyperosmotic conditions and a drop in growth temperature. The importance of the YycFG system and the transition-state regulator AbrB onto the induction of the yocH promoter under hyperosmotic condtions and at low temperature (15°C) could be shown in detail.