Influence of environment in host cells on heterogeneity of virulence factors expression in Salmonella

Bacteria of the genus Salmonella are one of the most important human pathogens. Salmonella expresses several virulence factors, including the type three secretion system encoded on the Salmonella pathogenicity island 2 (SPI-2 T3SS) and its effector proteins. SPI- 2 T3SS effector proteins allow the bacteria to colonize host cells, persist there and use them as a Trojan horse for migration throughout the host organism. Although the function of the SPI- 2 T3SS is essential for the bacterial population during systemic infection, some bacteria do not express this virulence factor and benefit from its expression by other members of the population. Similar heterogeneity in expression of other virulence factors has been shown to be crucial for their function. This work focuses on the heterogeneity of expression of selected SPI-2 T3SS effector proteins under the influence of host factors (pH, ROS, RNS) affecting bacteria during intracellular infection of macrophages. Using a fluorescent reporter system suitable for flow cytometry the expression of selected effector proteins was detected at the level of individual bacteria. The obtained data show, that individual bacteria respond differently to the decrease in pH in their vicinity. Part of the bacterial population starts to express the studied effector..