Hierarchical gene regulators adapt Salmonella enterica to its host milieus

The facultative intracellular pathogen Salmonella enterica serovar Typhimurium possesses an elaborate set of virulence genes that enables the bacterium successfully to move between and adapt to the environment, different host organisms and various micro-niches within a given host. Expression of virulence attributes is by no means constitutive. Rather, the regulation of virulence determinants is highly coordinated and integrated into normal bacterial physiological responses. By integrating discriminating virulence gene regulators with conserved housekeeping regulatory processes, the bacteria can sense alterations in the repertoire of environmental cues, and translate the sensing events into a pragmatic and coordinated expression of virulence genes. While the description of transmissible genetic elements that import global gene regulatory factors into a cell brings conceptual problems into the established regulatory network, the existence of mobile gene regulators may actually enable the bacteria to further modulate virulence expression.