Regulation of Staphylococcus aureus type 5 and type 8 capsular polysaccharides by CO2

Staphylococcus aureus expression of capsular polysaccharide type 5 (CP5) ha s been shown to be downregulated by CO2. Here we show that CO2 reduces CP5 expression at the transcriptional level and that CO2 regulates CP8 expressi on dpending on the genetic background of the strains. Growth in the presenc e of air supplemented with 5% CO2 caused a significant decrease in CP8 expr ession in four S. aureus strains, a marginal effect in four strains, and hi gher CP8 expression in strain Becker. Absolute CPS expression in the nine S . aureus strains differed largely from strain to strain. Four groups of str ains were established due to sequence variations in the promoter region of cap5 and cap8. To test whether these sequence variations are responsible fo r the different responses to CO2, promoter regions from selected strains we re fused to the reporter gene xylE in pLC4, and the plasmids were electrotr ansformed into strains Becker and Newman. XylE activity was negatively regu lated by CO2 in all derivatives of strain Newman and was always positively regulated by CO2 in all derivatives of strain Becker. Differences in promot er sequences did not influence the pattern of CP8 expression. Therefore, th e genetic background of the strains rather than differences in the promoter sequence determines the CO2 response. trans-acting regulatory molecules ma y be differentially expressed in strain Becker versus strain Newman. The st rain dependency of the CP8 expression established in vitro was also seen in lung tissue sections of patients with cystic fibrosis infected with CPS-po sitive S. aureus strains.