Peptide utilization by Lactococcus lactis and Leuconostoc mesenteroides.

To explain the competition for nitrogenous nutrients observed in mixed strain cultures of Lactococcus lactis and Leuconostoc mesenteroides, the utilization of peptides as a source of essential amino acids for growth in a chemically defined medium was compared in 12 strains of dairy origin. Both species were multiple amino acid auxotrophs and harboured a large set of intracellular peptidases. Lactococcus lactis can use a wide variety of peptides up to 13 amino acid residues whereas Leuc. mesenteroides assimilated only shorter peptides containing up to seven amino acids. Growth was limited by the transport of peptides and not by their hydrolysis. The nutritional value of peptides varied with the strains and the composition of the peptides, L. lactis being advantaged over Leuc. mesenteroides.

Accumulation of casein-derived peptides during growth of proteinase-positive strains of Lactococcus lactis in milk: their contribution to subsequent bacterial growth is impaired by their internal transport.

To explain the limited nutritional value of milk cultured with proteinase-positive (Prt+) strains of Lactococcus lactis for the subsequent growth of dairy lactococci, we investigated further the time courses of modifications in the free amino acid and peptide contents of cultured milk. When growing in milk for up to 24 h, Prt+ strains of Lc. lactis progressively accumulated amino acids and casein-derived peptides. The growth of proteinase-negative (Prt-) wild-type strains and peptide transport mutants of Lc. lactis in cultured milk showed that casein-derived peptides could sustain growth up to 5 x 10(8) cfu/ml, depending on the extent of casein degradation during the preliminary growth of Prt+ strains and the Prt- strains. Of the casein-derived oligopeptides, < 25% were transported into the cell and used for Lc. lactis growth. However, they played a prominent role, contributing 90% to growth. In contrast, di- and tripeptides did not contribute to growth, suggesting that either few were released from caseins or they did not supply essential amino acids.

[Inhibitory activity of sera from infected goats on syncitia formation due to caprine arthritis and encephalitis virus (CAEV)]. / Activité inhibitrice des sérums de chèvres infectées sur la formation de syncitia dus au virus de l'arthrite et de l'encéphalite (CAEV).

A very small number of goat positive for caprine arthritis encephalitis virus are also capable of in vitro inhibition of specific tissue culture lesions. This neutralizing activity for apparition of multinucleated cells is present in sera at low dilutions. We found this seric activity under natural conditions in young goats and in culled animals. Under experimental conditions the inhibitory activity was shown in the serum in a goat infected during gestation and in two animals infected when treated with repeated cortisone injection. The presence of syncitia formation inhibitory activity in sera seems to be related with virus reactivation.