MICROBIOLOGY: What's in a Name? -- Chin 309 (5734): 536d -- Science:
The human pathogen Staphylococcus aureus exhibits a golden hue, which comes from a carotenoid that is made by joining two molecules of farnesyl pyrophosphate, a reaction that is catalyzed by dehydrosqualene synthase (encoded by the gene crtM). Liu et al.have looked closely at this bacterium and find that its pigment is in fact a defensive weapon. Deleting crtM changed S. aureus color from gold to pale yellow and increased its sensitivity to being killed by reactive oxygen species (ROS). Conversely, adding this gene to another human pathogen, Streptococcus pyogenes, enhanced its color as well as its resistance to singlet oxygen. Survival of crtM-deleted S. aureus when challenged by human neutrophils or by whole blood from mice and humans was much lower than for wild-type bacteria. Protection could be conferred by an inhibitor of NADPH oxidase, which generates ROS; this was consistent with no difference in the survival of mutant and wild-type bacteria when cocultured with blood from a patient with chronic granulomatous disease (CGD; caused by NADPH oxidase deficiency) or from a mouse model of human CGD. Taken together, these results suggest that inhibition of carotenoid synthesis may render S. aureus more susceptible to host immune defenses.
The evolution of infectious agents has obvious importance.