A urease-deficient derivative of Streptococcus salivarius 57.I was construc
ted by allelic exchange at the ureC locus. The wild-type strain was protect
ed against acid killing through hydrolysis of physiologically relevant conc
entrations of urea, whereas the mutant was not. Also, S. salivarius could u
se urea as a source of nitrogen for growth exclusively through a urease-dep
endent pathway.