Polar localization of the chemotaxis system in Pseudomonas putida

It is important for bacteria to be able to perceive and react to changes in their environment. This includes positive changes in the nutrient gradient, i.e. an attractant that would trigger movement towards the substance, as well as low concentrations and deterrents that trigger movement away from it. The bacterial chemotaxis system can sense these gradient changes and transmit them via a signaling cascade within the cell to the designated flagellar motors. In the lophotrichous flagellated bacterium Pseudomonas putida, the chemotaxis system, like the flagella, is localized to the cell pole. To investigate the factors contributing to the polar localization of the chemotaxis system, deletion mutants of various proteins (e.g. FlhF, FimV and PocB) were generated that have previously been shown to be involved in the recruitment and correct localization of motility structures in Pseudomonads. Using a genomic translational fusion of CheA-mCherry, the localization of the chemotaxis system in the deletion strains was detected via fluorescence microscopy. In addition, the spreading behavior of the strains was examined. Our results indicate that deletions of a CheW domain protein and a ParA-family protein lead to a strong delocalization of the chemotaxis system, whereas deletions of FlhF and PocB have only a minor effect. Remarkably, the deletion of FimV does not result in delocalization of the chemotaxis system. In addition, a deletion of FlhF significantly reduces the number of cells with a chemotaxis system. The spreading behavior of P. putida is substantially influenced by all deletions. The study shows that the mechanism underlying polar localization of the P. putida chemotaxis system differs from that of other monopolarly flagellated gammaproteobacteria and potentially also from that of other Pseudomonas species.