Oligopeptides are the main source of nitrogen for Lactococcus lactis during growth in milk

Abstract

The consumption of amino acids and peptides was monitored during growth in milk of proteinase-positive (Prt ؉) and-negative (Prt ؊) strains of Lactococcus lactis. The Prt ؊ strains showed monophasic exponential growth, while the Prt ؉ strains grew in two phases. The first growth phases of the Prt ؉ and Prt ؊ strains were the same, and no hydrolysis of casein was observed. Also, the levels of consumption of amino acids and peptides in the Prt ؉ and Prt ؊ strains were similar. At the end of this growth phase, not all free amino acids and peptides were used, indicating that the remaining free amino acids and peptides were unable to sustain growth. The consumption of free amino acids was very low (about 5 mg/liter), suggesting that these nitrogen sources play only a minor role in growth. Oligopeptide transport-deficient strains (Opp ؊) of L. lactis were unable to utilize oligopeptides and grew poorly in milk. However, a di-and tripeptide transport-deficient strain (DtpT ؊) grew exactly like the wild type (Opp ؉ DtpT ؉) did. These observations indicate that oligopeptides represent the main nitrogen source for growth in milk during the first growth phase. In the second phase of growth of Prt ؉ strains, milk proteins are hydrolyzed to peptides by the proteinase. Several of the oligopeptides formed are taken up and hydrolyzed internally by peptidases to amino acids, several of which are subsequently released into the medium (see also E.

Utilization of amino acids and dipeptides by Lactobacillus plantarum from orange in nutritionally stressed conditions

“…However, none of the amino acids were completely utilized, when bacterial growth stopped, indicating that some other compound(s) were lacking in the medium. Similar results were reported by Juillard et al (1995) for L. lactis growing in milk. As the greatest amount of amino acid utilization was observed in the presence of both dipeptides (Fig.…”

From meadows to milk to mucosa – adaptation ofStreptococcusandLactococcusspecies to their nutritional environments

“…While many anaerobic bacteria utilize sugars in the ways described above, lactococci and streptococci are unique in their avoidance of de novo synthesis of many macromolecular building blocks, especially amino acids (Juillard et al, 1995;Poolman & Konings, 1988). These bacteria therefore make great nutritional demands on the growth medium, which are accommodated by a wide variety of substrate transporters (Poolman, 1993).…”

“…This genetic element is normally not present in the dairy-derived strains and is spontaneously lost upon prolonged growth of L. lactis KF147 in milk (Bachmann, 2009). Milk contains very low amounts of free amino acids and peptides, and L. lactis ssp., having low amino acid biosynthetic capabilities, may depend on a proteolytic system that allows the degradation and utilization of the predominant protein in bovine milkcasein (Mills & Thomas, 1981;Juillard et al, 1995). Casein contains all the amino acids necessary for the growth of L. lactis.…”

Osmotic‐Convective Dehydrofreezing Process for Drying Kiwifruit

“…As growth media ingredients, YE have been shown to stimulate growth of lactic acid bacteria . Amino acids (Benthin and Villadsen, 1996;Juillard et al, 1995), nucleotides and inorganic constituents have been shown to be growth stimulators for lactococci . Autolysates and yeasts extracts are used in culture media at Ͻ10 g/L, but yeast extract solutions obtained at the end of the autolytic process have Ͼ70 g/L soluble solids.…”