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Dependence of growth characteristics of original strains of Lactococcus lactis subsp. lactis on the composition of agar media used for biomass growth

Trenina, M. A., Yepremyan, A. S., Stoyanova, L. G.
Moscow University biological sciences bulletin 2015 v.70 no.1 pp. 29-34
Lactococcus lactis subsp. lactis, acidity, agar, bacteria, biomass production, casein, cell division, lactic acid, meat extracts, milk, nitrogen, pH, peptones, yeast extract
Data on the dependence of growth characteristics of Lactococcus lactis subsp. lactis 729 and TB2 extracted from milk and homemade curd on the content of casein peptone (CP) as the main source of nitrogen in the agar medium is presented. The number of colony-forming units (CFUs), cell division rate (CDR), and mean hourly doubling time (HDT) were compared between two time segments of cultivation: from 1 to 2.5 h, and from 2.5 to 3.5 h. In liquid media, logarithmic growth was observed for the 729 strain in all groups for 3.5 h at minimal pH of 6.5. The maximum biomass production rate (2.5 × 10⁸cells/mL) was observed in the media containing the meat extract; the minimal HDT was in the biomass transferred from the minimal MA4 medium to the enriched M7 medium. In contrast with the TB2 strain, the 729 strain does not form colonies on agar media at CP concentrations below 0.4%. The colonies of the TB2 strain increase in size from 2.85 mm²to 5 mm²when decreasing CP concentration from 1 to 0.4%. The yeast extract has a stimulating effect in liquid media at said concentration ratios, leading to an increase in the efficiency of cell division at lower rates of lactic acid production, to pH of 5.5 when oligopeptide transport is blocked. The meat extract provides adaptation of bacteria to the conditions of excessive acidity and has positive effect on cell division in the 729 strain at later stages of bacterial colony development. The smaller size of colonies of the strain might be evidence of active acid formation.