RATIONAL DEVELOPMENT OF A SIMPLE SYNTHETIC MEDIUM FOR THE SUSTAINED GROWTH OF LACTOCOCCUS-LACTIS

The growth of two strains of Lactococcus lactis subsp. lactis from veg etable (NCDO 2118) and dairy origin (IL 1403) were compared on various culture media. Both strains grew more rapidly on a complex organic me dium than on a defined synthetic medium. The best growth was obtained under nitrogen gas phase. The single omission technique was applied to each component of a non-optimized synthetic medium in order to determ ine the true nutritional requirements. Requirements for macro-elements , oligo-elements, bases and vitamins were identical for the two strain s. As expected, the dairy strain (IL 2403) was seen to be auxotrophic for some amino acids, whereas the vegetable strain (NCDO 2118) was see n to be prototrophic for ah amino acids when using the single omission technique. Growth was then characterized on progressively simplified media and the composition of the absolute minimal media for the growth of both strains was defined. Sustained growth of the vegetable strain was only possible in minimal media supplemented with six amino acids (Glu, Met, IIe, Leu, Val, Ser), indicating that the definition of prot otrophy/auxotrophy is partly dependent upon the medium composition. Th e dairy strain showed a requirement for Arg, His and Thr in addition t o the six amino acids necessary for growth of the vegetable strain. Th e removal of ammonium salt from the medium did not affect the growth, illustrating that the amino acids may satisfy the totality of the nitr ogen requirement for biomass synthesis.