Effects of rodA and pbp2b disruption on cell morphology and oxidative stress response of Streptococcus thermophilus CNRZ368

Insertional mutagenesis was used to isolate clones from Streptococcus thermophilus CNRZ368 that were modified in their abilities to tolerate oxidative stress. During this process, two menadione-sensitive clones (6G4 and 18C3) were found to display abnormal cell morphologies and distorted chain topologies and were further studied. Molecular characterization of both 6G4 and 18C3 mutants indicated that they were disrupted in open reading frames homologous to rodA and pbp2b, respectively. Both genes encoded proteins in Escherichia coli that were described as being implicated in peptidoglycan synthesis during the process of cell elongation and to function in determining the rod shape of the cell. This work reports a possible connection between peptidoglycan biosynthesis and oxidative stress defense in S. thermophilus CNRZ368.