NUTRITIONAL-REQUIREMENTS OF LACTIC-ACID B ACTERIA - INTERACTIONS BETWEEN CARBON AND NITROGEN FLUX

Nutritional requirements have been determined for two strains of Lacto coccus lactis subsp lactis. The IL 1403 dairy strain, was shown to be auxotroph for nine amino acids and five vitamins, while the NCDO 2118 strain isolated from vegetable matter was prototroph for all amino aci ds when using the single omission technique, but nevertheless required six amino acids and five vitamins for growth in minimal medium. In su ch a medium, the suppression of glutamate led to a lag phase of about 2 days and a decrease of the growth rate. The problem of glutamate syn thesis is linked to the part of Krebs cycle between oxaloacetate and a lpha-ketoglutarate, and to the glutamate dehydrogenase. Concerning the branched-chain amino acids, not only has the regulation of acetolacta te decarboxylase been confirmed, but the regulation of acetohydroxy ac id synthase(s) by threonine and thiamine has also been observed Both t he consumption and the synthesis of serine are regulated by other amin o acids or vitamins. Serine consumption is about 12 times higher in th e minimal medium than in a medium containing 18 aminoacids. The study of C-14-serine distribution showed that it is deaminated and transform ed to lactate.