Significance of the chromosomal positions of the genes encoding DNA gyrase in Salmonella enterica Serovar Typhimurium

Changing positions of genes on a chromosome is an informative way of learning about why an existing chromosome structure and gene order was selected by evolution in bacteria. In Salmonella gyrA and gyrB – genes encoding DNA gyrase – enzyme that introduces negative supercoils in DNA, are located almost at opposite poles of a chromosome. However, in many other bacteria they are arranged in a gyrBA operon. In order to investigate the significance of this fact, gyrBA operon was made in Salmonella by bringing gyrA open reading frame and its ribosome binding site directly downstream of gyrB and under a control of its regulatory regions, the original copy of gyrA was deleted. The gyrBA strain obtained as a result exhibits no differences from the wild type in growth and morphology, however, the ability to supercoil DNA is altered between gyrBA and the WT. This is specifically important at conditions mimicking environment inside a macrophage in terms of Mg2+ concentration, as it may suggest alteration of gyrBA survival inside a macrophage. An attempt to make strain with gyrAB operon was not successful, as it was not possible to delete the original gyrB, suggesting particular importance of its position.