ABSTRACT

Compared to cells of multicellular organisms, microorganisms face a significant additional challenge: they encounter a wide array of sudden, intense and sometimes even life-threatening environmental changes, and must therefore rapidly modify their structure and metabolism accordingly. Although other mechanisms exist, these changes in bacterial physiology mainly occur by regulating the production of the appropriate structural proteins and enzymes. Adaptation of gene expression in response to such situations appears to be essential for bacterial survival, and thus the regulators involved in these processes should be treated as being as important as the effectors themselves. In bacterial pathogens like those of the Yersinia genus, most outside-to-inside stress-induced

responses lead to changes in the expression of virulence factors. In fact, most of the known Yersinia virulence genes are regulated, and elements controlling their expression are thus also virulence factors.