The role of aminopeptidase PepS in the growth of Streptococcus thermophilus is not restricted to nitrogen nutrition

Aims:  To investigate the effect of an absence of aminopeptidase PepS on the growth of Streptococcus thermophilus on different media and at different temperatures.
Methods and Results:  Using gene interruption, a negative mutant of the Strep. thermophilus CNRZ385 strain was constructed for the aminopeptidase PepS (strain Δ pepS ). Checks were first of all made using biochemical assays that the Δ pepS strain lacks the peptide hydrolase activity of aminopeptidase PepS. It was demonstrated that the absence of the aminopeptidase PepS exerted a negative effect on growth whatever the culture medium (M17, chemically defined medium, milk). The role of aminopeptidase PepS in growth was enhanced at a high temperature (45°C vs 37°C). The Δ pepS strain was more resistant to lysozyme than the wild-type strain .
Conclusions:  We were able to demonstrate that aminopeptidase PepS probably plays a pleiotropic role through its involvement in growth via nitrogen nutrition, as well as via other cellular functions/metabolisms (such as peptidoglycane metabolism).
Significance and Impact of the Study:  This study constitutes the first report on the role of a member of the M29 MEROPS family of metallopeptidases ( http://merops.sanger.ac.uk/ ).