ASSOCIATIVE GROWTH OF LACTOCOCCUS-LACTIS AND LEUCONOSTOC-MESENTEROIDES STRAINS IN MILK

The associative growth of a proteinase-positive strain of Lactococcus lactis ssp. lactis CNRZ 1076 and Leuconostoc mesenteroides ssp. mesent eroides UM10 in reconstituted skim milk was studied in detail. The max imum population and the growth rate of Lc. lactis CNRZ 1076 were not a ffected by the association between strains. The growth rate of Leuc. m esenteroides UM10 was lower in mixed-strain cultures than in pure cult ure (0.40 vs. 0.63/h, respectively), and the maximum population was 10 -fold lower. Acidification was essentially due to the action of Lc. la ctis CNRZ 1076, and the acidification rate in mixed-strain cultures an d in pure cultures were comparable except when the percentage of Lc. l actis cells was lower than 12%. Inhibition of Leuc. mesenteroides grow th was less when the percentage of Lc. lactis cells was lower in the i noculum. inhibition was almost suppressed when reconstituted skim milk was supplemented with amino acids, MN2+, and Mg2+. Twenty-four paired associative cultures of 3 Lc. lactis strains and 8 Leuc. mesenteroide s strains in reconstituted skim milk confirmed that competition betwee n the two species for nitrogenous nutrients is a common feature of mix ed-strain cultures, regardless of the subspecies of Leuc. mesenteroide s or Lc. lactis strains used.