Changes in availability of oxygen accentuate differences in capsular polysaccharide expression by phenotypic variants and clinical isolates of Streptococcus pneumoniae

Most isolates of Streptococcus pneumoniae are mixed populations of transpar ent (T) and opaque (O) colony phenotypes. Differences in the production of capsular polysaccharide (CPS) between O and T variants were accentuated by changes in the environmental concentration of oxygen. O variants demonstrat ed a 5.2- to 10.6-fold increase in amounts of CPS under anaerobic compared to atmospheric growth conditions, while CPS production remained low under a ll conditions for T variants. Increased amounts of CPS in O compared to T p neumococci were associated with increased expression of cps-encoded protein s. The inhibitory effect of oxygen on expression of CPS in O variants corre lated with decreased tyrosine phosphorylation of CpsD, a tyrosine kinase an d regulator of CPS synthesis. Modulation of CpsD expression and its activit y by tyrosine phosphorylation may allow the pneumococcus to adapt to the re quirements of both colonization, where decreased CPS allows for adherence, and bacteremia, where increased CPS may be required to escape from opsonic clearance. In patients with invasive infection, paired isolates from the sa me patient were shown to have predominately a T colony phenotype without ph osphotyrosine on CpsD when cultured from the nasopharynx, and an O phenotyp e that phosphorylates CpsD in response to oxygen when cultured from the blo od. Differences in the availability of oxygen, therefore, may be a key fact or in allowing for the selection of distinct phenotypes in these two host e nvironments.