Genetic and physiological analysis of the lethal effect of L-(+)-lactate dehydrogenase deficiency in Streptococcus mutans: complementation by alcohol dehydrogenase from Zymomonas mobilis.
CH4ts is a previously isolated recombinant mutant of Streptococcus mutans NG8 which produces a thermolabile L-(+)-lactate dehydrogenase (LDH) activity. It does not grow at 42 degrees C under a variety of cultivation conditions. In this study, we show that a batch culture of CH4ts shifted from 30 to 42 degrees C underwent rapid cessation of growth and accelerated cell death. The mutant grew at 42 degrees C in continuous culture under glucose-limiting conditions. Under these conditions, lactate production was replaced by production of ethanol and, to a smaller extent, acetoin. The cloned Zymomonas mobilis gene for alcohol dehydrogenase II, placed under the control of the S. mutans spaP regulatory signals, complemented LDH deficiency. The alcohol dehydrogenase-complemented mutant grew as well or better than NG8 on a variety of carbon sources at 42 degrees C and produced significant amounts of ethanol in place of lactic acid. These results are in accord with other approaches indicating that S. mutans has other enzymatic activities, including pyruvate formate-lyase and pyruvate dehydrogenase, for pyruvate metabolism. However, at high glucose concentrations, the levels of activity of these enzymes are apparently insufficient to compensate for the absence of LDH.
Hillman
J D
JD
Department of Oral Biology, University of Florida College of Dentistry, Gainesville 32610, USA. jhillman@dental.ufl.edu
Chen
A
A
Snoep
J L
JL
D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000172:deficiency*; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D017355:Zymomonas / Q000201:enzymology*
D000426:Alcohol Dehydrogenase; D007770:L-Lactate Dehydrogenase; D005947:Glucose