Environmental regulation of the pneumolysin gene of Streptococcus pneumoniae

Streptococcus pneumoniae (the pneumococcus), a major cause of morbidity and mortality throughout the world, is responsible for the life threatening diseases pneumonia and meningitis. Numerous virulence factors are believed to be involved in the disease process, including the cytolytic toxin pneumolysin. This toxin has been studied in detail in terms of its structure and function. Little is known about the expression and regulation of this toxin. It is also unknown whether any of the other virulence factors are regulated.;Environmental regulation of the pneumolysin gene was studied. The effect of temperature, adding serum to the growth medium, pH, and iron, on the expression of the pneumolysin gene was studied. Initial experiments, whereby toxin levels were measured directly by ELISA, indicated that pneumolysin expression is increased in a low iron environment, compared with an iron replete medium.;A luciferase and a cat reporter fusion, with DNA from immediately upstream of the pneumolysin gene, confirmed the observation that pneumolysin expression is increased in a low iron environment.;Regulation of the pneumolysin gene was also studied at the transcriptional level. Northern blot analysis revealed that the pneumolysin gene is transcribed as part of a polycistronic message along with two open reading frames located upstream and possibly a third located downstream. Primer extension analysis identified a putative transcriptional start site 90bp upstream of ORF1 and another 300bp upstream of the pneumolysin gene. A model of the proposed mechanism of regulation of pneumolysin expression is presented.