EFFECT OF AMINO-ACIDS ON STREPTOCOCCUS-SALIVARIUS SUBSP THERMOPHILUS GROWTH IN MODIFIED MILK DEPRIVED OF NONPROTEIN NITROGEN FRACTION

Streptococcus salivarius subsp. thermophilus has large requirements fo r nutritional factors essential for its growth. The aim of this work w as to obtain more information about the effects of amino acids on its metabolism. The influence of 18 amino acids on growth of 17 Str. saliv arius subsp. thermophilus strains was investigated using the conductim etric technique. The variation in the metabolic activity of the strain s was evaluated as a function of the addition of individual amino acid s to a culture medium containing skim milk deprived of the soluble nit rogen fraction by ultrafiltration-diafiltration. Results showed that S tr. salivarius subsp. thermophilus growth was inhibited in a substrate poor in soluble nitrogen. Amino acids with both stimulating and inhib iting effects on the metabolic activity were identified.