Catalase-peroxidases of Legionella pneumophila: Cloning of the katA gene and studies of KatA function

Legionella pneumophila, the causative organism of Legionnaires' pneumonia, contains two enzymes with catalatic and peroxidatic activity, KatA and KatB . To address the issue of redundant, overlapping, or discrete in vivo funct ions of highly homologous catalase-peroxidases, the gene for katA was clone d and its function was studied in L. pneumophila and Escherichia coli and c ompared with prior studies of katB in this laboratory. katA is induced duri ng exponential growth and is the predominant peroxidase in stationary phase . When katA is inactivated, L. pneumophila is more sensitive to exogenous h ydrogen peroxide and less virulent in the THP-1 macrophage cell line, simil ar to katB. Catalatic-peroxidatic activity with different peroxidatic cosub strates is comparable for KatA and KatB, hut KatA is Ave times more active towards dianisidine. In contrast with these examples of redundant or overla pping function, stationary-phase survival is decreased by 100- to 10,000-fo ld when katA is inactivated, while no change from wild type is seen for the katB null. The principal clue for understanding this discrete in vivo func tion was the demonstration that KatA is periplasmic and KatB is cytosolic. This stationary-phase phenotype suggests that targets sensitive to hydrogen peroxide are present outside the cytosol in stationary phase or that the p eroxidatic activity of KatA is critical for stationary-phase redox reaction s in the periplasm, perhaps disulfide bond formation. Since starvation-indu ced stationary phase is a prerequisite to acquisition of virulence by L. pn eumophila, further studies on the function and regulation of katA in statio nary phase may give insights on the mechanisms of infectivity of this patho gen.