ISOLATION AND PROPERTIES OF LACTOCOCCUS-LACTIS SUBSP LACTIS BIOVAR DIACETYLACTIS CNRZ-453 MUTANTS PRODUCING DIACETYL AND ACETOIN FROM GLUCOSE

Following treatment with the mutagen N-methyl-N'-nitro-N-nitrosoguanid ine, three mutants of Lactococcus lactis subsp. lactis biovar diacetyl actis CNRZ 483 that produced diacetyl and acetoin from glucose were is olated. The lactate dehydrogenase activity of these mutants was strong ly attenuated, and the mutants produced less lactate than the parental strain. The kinetic properties of lactate dehydrogenase of strain CNR Z 483 and the mutants revealed differences in the affinity of the enzy me for pyruvate, NADH, and fructose-1,6-diphosphate. When cultured aer obically, strain CNRZ 483 transformed 2.3% of glucose to acetoin and p roduced no diacetyl or 2,3-butanediol. Under the same conditions, muta nts 483L1, 483L2, and 483L3 transformed 42.0, 78.9, and 75,8%, respect ively, of glucose to C-4 compounds (diacetyl, acetoin, and 2,3-butaned iol). Anaerobically, strain CNRZ 483 produced no C-4 compounds, while mutants 483L1, 483L2, and 483L3 transformed 2.0, 37.0, and 25.8% of gl ucose to acetoin and 2,3-butanediol. In contrast to the parental strai n, the NADH balance showed that the mutants regenerated most of the NA D via NADH oxidase under aerobic conditions and by ethanol production under anaerobic conditions.