Functional assessment of microbial superoxide dismutase isozymes suggests a differential role for each isozyme

Microbes can have multiple enzymes that are able to catalyse the same enzymatic reactions but may differ in structure. These are known as isozymes. It is assumed that isozymes have the same functional role for cells. Contrary to this assumption, we hypothesised that isozymes can confer different functions for microbial cells despite catalysing the same reactions. To test this hypothesis, we studied the role of superoxide dismutases (SOD) in Klebsiella pneumoniae, the causative agent of several nosocomial and community-acquired infections, in infection relevant assays. SODs are responsible for detoxification of toxic superoxide radicals. K. pneumoniae genome contains three superoxide dismutase genes, sodA, sodB, and sodC coding for Mn-, Fe- and CuZn- co-factored SODs, respectively. By creating and testing single, double, and triple SOD mutants, we investigated the regulatory interactions among SOD and determined the role of each isozyme in oxidative stress resistance, biofilm formation, cell morphology, metabolism, and in vivo colonization and persistence. Our results demonstrate that SOD isozymes in K. pneumoniae have unique roles beyond oxidative stress resistance, and there is a regulatory interplay among SODs.