Regulation in Response to Environmental Conditions

Abstract

This chapter discusses what is currently known regarding how and why a few of the most important human respiratory pathogens control gene expression in response to environmental conditions. Even less well characterized is the ability of Haemophilus influenzae to control gene expression in response to environmental conditions. Like Neisseria meningitidis and H. influenzae, Streptococcus pneumoniae expresses a polysaccharide capsule that plays a major role in pathogenesis. Understanding how these regulators coordinate to mediate precise control of capsule and other virulence factors in response to specific environmental conditions awaits further study. Comparative analyses between S. pneumoniae and Streptococcus pyogenes should facilitate understanding the structure and function of the Mga/MgrA regulons of these two streptococcal species. Roles for the other two, or for the C-terminal domain of the protein, remain to be determined, but there is presently no evidence that Mga protein activity is controlled in response to environmental conditions. Bordetella pertussis does not cause severe invasive or systemic disease, although serious complications, including pneumonia, seizures, encephalopathy, and even death, sometimes occur. Natural-host animal models were recently developed to allow the study of the entire infectious cycle in the laboratory. Comparison of mutants altered in signal transduction and/or in Bvg-mediated control of specific factors in these models is expected to allow one to gain a better understanding of the importance of precise control of gene expression in the establishment, maintenance, and transmission of Bordetella infection.