Journal of Dental Research, Vol 64, 1191-1194, Copyright © 1985 by International & American Associations for Dental Research Online Journals
Lactate dehydrogenase-deficient mutants of serotype g Streptococcus mutans
H. H. Salem, H. J. Sandham and K. H. Chan
Three LDH-deficient mutants of a serotype g strain of Streptococcus mutans
were produced essentially as described by Hillman (1978): They were
produced using ethylmethane sulfonate, and isolated using
triphenyltetrazolium-glucose agar. Similar attempts to obtain mutants from
a serotype c strain were unsuccessful. The g mutant did not revert during
12 weeks of daily transfer in broth, and, when grown in glucose-containing
broth, they reached pH values of 4.9 to 5.0, compared with 4.4 for the
parent strain. The efficiency of conversion of glucose to cell mass (Yg)
was at least as great with the mutants as with the parent strain. The LDH
activities of the mutants were less than 1% of that of the parent strain.
Like Hillman's (1978) mutants, ethanol, acetic acid, and acetoin were the
major products resulting from the metabolism of glucose. Although at pH 7.0
the mutants grew more slowly than did the parent, at pH 5 and pH 6 one of
the mutants grew as rapidly as did the parent. The stability, serotype, and
ability of these mutants to grow at low pH suggest their potential
usefulness for replacement therapy.
