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 mut ans NG8 which produces a thermolabile L-(+)-lactate dehydrogenase (LDH ) activity, It does not grow at 42 degrees C under a variety of cultiv ation conditions, In this study, we show that a batch culture of CH4ts shifted from 30 to 42 degrees C underwent rapid cessation of growth a nd accelerated cell death, The mutant grew at 42 degrees C in continuo us culture under glucose-limiting conditions, Under these conditions, lactate production was replaced by production of ethanol and, to a sma ller extent, acetoin, The cloned Zymomonas mobilis gene for alcohol de hydrogenase II, placed under the control of the S. mutans spaP regulat ory signals, complemented LDH deficiency, The alcohol dehydrogenase-co mplemented mutant grew as well or better than NG8 on a variety of carb on sources at 42 degrees C and produced significant amounts of ethanol in place of lactic acid, These results are in accord with other appro aches indicating that S. mutans has other enzymatic activities, includ ing pyruvate formate-lyase and pyruvate dehydrogenase, for pyruvate me tabolism, However, at high glucose concentrations, the levels of activ ity of these enzymes are apparently insufficient to compensate for the absence of LDH.