Listeria seeligeri Gene Encoding Heme-containing Catalase Produces No Activity in Streptococcus pneumoniae

ABSTRACT

Streptococcus pneumoniae is a facultative anaerobe lacking catalase enzyme and requires exogenous catalase supplemented to culture media for aerobic growth. We introduced a catalase gene (kat) of Listeria seeligeri into S. pneumoniae and tried to see if this listerial kat gene was expressed within the pneumococcal host. To clone the listerial kat gene in the pneumococcal chromosome, a non-replicating plasmid pAHA-LSt3, along with its original promoter region was used for integration the chromosome via homologous recombination. One of three resulting transformants was confirmed to contain the kat gene and designated as EHS2. In addition, the kat gene was subcloned in Escherichia coli in frame to the lac promoter of a shuttle vector to generate pDL-Kat, which was subsequently used for pneumococcal transformation. Four identical recombinants were identified to contain the plasmid with the kat gene. By performing RT-PCR, it was observed that the listerial kat gene was indeed transcribed within pneumococcal recombinants from its original promoter in the chromosome of EHS2 and from the lac promoter in the plasmid pDL-Kat. In contrast to the E. coli kat+ recombinants, however, the pneumococcal kat+ recombinants failed to reveal any catalase activities detectable by ferricyanide staining on non-denaturing PAGE. When the pDL-Kat plasmid DNA purified from pneumococci was allowed to transform E. coli again, many kat+ recombinants were obtained, ruling out the possibility of the defective kat E. coli transformants gene within pneumococci. The observation that the listerial kat gene in pneumococci was unable to produce the functional catalase enzyme, which requires a heme group at its active site and a cofactor NADPH, suggests pneumococcal defect in heme production.