Identification and expression studies of a catalase and a bifunctional catalase-peroxidase in Frankia strain R43

A monofunctional catalase and a bifunctional catalase-peroxidase were revealed by activity staining of non-denaturing PAGE in Frankia strain R43. Both enzymes were shown to be cytoplasmatic, growth regulated and expressed mainly during the stationary growth phase. Nevertheless, low levels of constitutive expression could also be detected during the early stages of growth. Immunoblot analyses using a polyclonal antibody raised against a catalase-peroxidase purified from Streptomyces reticuli showed a band of 83.2 kDa, with the same growth dependent pattern as obtained by the non-denaturing PAGE analyses. Induction studies revealed that both enzymes were strongly induced by raising the intracellular concentration of H2O2 with paraquat, but not with exogenous H2O2. In addition, no acquisition of tolerance to exogenous H2O2 was observed whatever the pretreatment of the inocula, i.e. despite the expression level of both hydroperoxidases.