PERIPLASMIC COPPER-ZINC SUPEROXIDE-DISMUTASE OF LEGIONELLA-PNEUMOPHILA - ROLE IN STATIONARY-PHASE SURVIVAL

Copper-zinc superoxide dismutases (CuZnSODs) are infrequently found in bacteria although widespread in eukaryotes, Legionella pneumophila, t he causative organism of Legionnaires' disease, is one of a small numb er of bacterial species that contain a CuZnSOD, residing in the peripl asm, in addition to an iron SOD (FeSOD) in their cytoplasm, To investi gate CuZnSOD function, we purified the enzyme from wild-type L. pneumo phila, obtained amino acid sequence data from isolated peptides, clone d and sequenced the gene from a L. pneumophila library, and then const ructed and characterized a CuZnSOD null mutant, In contrast to the cyt oplasmic FeSOD, the CuZnSOD of L. pneumophila is not essential for via bility. However, CuZnSOD is critical for survival during the stationar y phase of growth, The CuZnSOD null mutant survived 10(4) to 10(6)-fol d less than wild-type L. pneumophila. In wild-type L. pneumophila, the specific activity of CuZnSOD increased during the transition from exp onential to stationary-phase growth while the FeSOD activity was const ant, These data support a role of periplasmic CuZnSOD in survival of L . pneumophila during stationary phase. Since L. pneumophila survives e xtensive periods of dormancy between growth within hosts, CuZnSOD may contribute to the ability of this bacterium to be a pathogen, In expon ential phase, wild-type and CuZnSOD null strains grew with comparable doubling times. In cultured HL-60 and THP-1 macrophage-like cell lines and in primary cultures of human monocytes, multiplication of the CuZ nSOD null mutant was comparable to that of wild type, This indicated t hat CuZnSOD is not essential for intracellular growth within macrophag es or for killing of macrophages in those systems.