The growth of two strains of Lactococcus lactis subsp. lactis from vegetable (NCDO 2118) and dairy origin (IL 1403) were compared on various culture media. Both strains grew more rapidly on a complex organic medium 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 determine the true nutritional requirements. Requirements for macro‐elements, oligo‐elements, bases and vitamins were identical for the two strains. As expected, the dairy strain (IL 1403) was seen to be auxotrophic for some amino acids, whereas the vegetable strain (NCDO 2118) was seen to be prototrophic for all 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, Ile, Leu, Val, Ser), indicating that the definition of prototrophy/auxotrophy is partly dependent upon the medium composition. The dairy strain showed a requirement for Arg, His and Thr in addition to the six amino acids necessary for growth of the vegetable strain. The removal of ammonium salt from the medium did not affect the growth, illustrating that the amino acids may satisfy the totality of the nitrogen requirement for biomass synthesis.

Lactococcus lactis NCDO 2118 was grown in a simple synthetic medium containing only six essential amino acids and glucose as carbon substrates to determine qualitatively and quantitatively the carbon fluxes into the metabolic network. The specific rates of substrate consumption, product formation, and biomass synthesis, calculated during the exponential growth phase, represented the carbon fluxes within the catabolic and anabolic pathways. The macromolecular composition of the biomass was measured to distribute the global anabolic flux into the specific anabolic pathways. Finally, the distribution of radiolabeled substrates, both into the excreted fermentation end products and into the different macromolecular fractions of biomass, was monitored. The classical end products of lactic acid metabolism (lactate, formate, and acetate) were labeled with glucose, which did not label other excreted products, and to a lesser extent with serine, which was deaminated to pyruvate and represented approximately 10% of the pyruvate flux. Other minor products, keto and hydroxy acids, were produced from glutamate and branched-chain amino acids via deamination and subsequent decarboxylation and/or reduction. Glucose labeled all biomass fractions and accounted for 66% of the cellular carbon, although this represented only 5% of the consumed glucose.Lactic acid bacteria (LAB) are of great importance in the food industry, mainly for lactic acid production from various substrates, but also for flavor compound or bacteriocin synthesis. The nutritional complexity of LAB is such that they are frequently cultivated in media containing complex nitrogen sources (MRS [9] or M17 [30]) or in natural media (milk or wine) for different applications. However, the complexity of these media is such that growth and metabolic behavior are difficult to characterize precisely. This is certainly the reason why it is generally considered that during LAB fermentation, sugar is only a catabolic substrate leading to metabolic end products and energy while biomass is formed from anabolic precursors, i.e., amino acids, nucleotides, etc., present in the culture broth. Whatever the medium used, more than 90% of the carbon in the sugar is normally converted into metabolic end products, generally, lactic acid. Moreover, the growth of LAB is characterized by poor growth yield, i.e., amount of biomass formed per amount sugar consumed, and hence, the quantity of the biomass formed is low compared to the quantity of lactic acid produced. However, this simplistic model is based on inaccurate carbon balances and is very controversial. A very small part of the sugar leading to anabolic reactions could represent a significant part of the biomass carbon, and this consideration has been totally neglected.The study of radiolabeled substrate distribution into end products or biomass has been used to estimate the part of sugar leading to biomass. Sivakanesan and Dawes (29) reported that 0.5% of the glucose used as the substrate labeled the biomass of Staphylococcus epidermi...

When Lactococcus lactis was grown in various complex or synthetic media, the fermentation of glucose remained homolactic whatever the medium used, with a global carbon balance of about 87%. Moreover, the nitrogen balance was not equilibrated, indicating that some amino acids led to the production of unknown nitrogen-containing carbon compounds while part of the glucose might contribute to anabolic pathways. In minimal medium containing six amino acids, a high concentration of serine was deaminated to pyruvate. This did not occur in more complete media, suggesting the presence of a regulation of this phenomenon by an amino acid. Ammonia produced during serine consumption was partly reconsumed after serine exhaustion. The values for biomass yield and biomass yield relative to ATP (Y ATP), the maximal growth rate, the specific rate of glucose consumption, and the corresponding rate of ATP synthesis all increased with the complexity of the medium, amino acid composition having the most pronounced effect. The Y ATP values were shown to range from 6.6 to 17.6 g of biomass ⅐ mol of ATP ؊1 on minimal and complex media.