On 18 September at 14:15 Kadi Tilk will defend her doctoral thesis in genetics “Signals and responses of ColRS two-component system in Pseudomonas putida“
Supervisor: Senior research fellow Rita Hõrak, the Institute of Molecular and Cell Biology.
Opponent: professor Thorsten Mascher, Chair of General Microbiology, lnstitute of Microbiology, Technische Universität Dresden (Germany).
Bacteria can be found almost everywhere. Some of them are adapted to life in soil, while others feel themselves at home in water, on plants, inside the gut or on the skin. In nature, the conditions around bacteria are constantly changing. For example, the temperature can change within hours, the nutrients can be sufficient in one day and deprived in other and the pH in the environment can be shifted due to the byproducts of the bacteria themselves.
To determine the conditions around them, bacteria use signaling systems consisting of two proteins. The first protein, histidine kinase, is usually located at the surface of the bacterium and detects the presence of a certain signal or condition. In response to detecting the signal, the histidine kinase activates another protein, the response regulator. Response regulator is inside the bacterium and in an active state changes the physiology of the bacterium by altering, for example, gene expression.
The focus of this thesis was one two-component system that can be found in soil and plant bacteria – the ColRS system, named after being necessary for colonizing plant roots. We found that for soil bacterium Pseudomonas putida this system detects the presence of excess amount of zinc, iron, manganese and cadmium in the extracellular environment. Although, zinc, iron and manganese are necessary for bacteria, their excess is harmful. Metal ions can damage the membrane of the bacterium, its proteins and also its DNA. If the ColRS system is absent in P. putida, it is sensitive to zinc and iron and has a slightly decreased tolerance for manganese. Therefore, we propose that the main role of the ColRS system is to sense the excess of zinc and iron.
Previous studies with the ColRS system have indicated that the system is required for maintaining membrane integrity. The results of this thesis also suggest that the importance of ColRS system in zinc excess lies in preventing membrane damage. The activation of the ColRS system induces a response that helps to maintain membrane integrity and thereby prevents the metal ions from entering the cell.