Kinetics ofLactococcus lactis growth and metabolite formation under aerobic and anaerobic conditions in the presence or absence of hemin

Abstract

The study of batch kinetics of Lactococcus lactis cell growth and product formation reveals three distinct metabolic behaviors depending upon the availability of oxygen to the culture and the presence of hemin in the medium. These three cultivation modes, anerobic homolactic fermentation, aerobic heterolactic fermentation, and hemin-stimulated respiration have been studied at pH 6.0 and 30 degrees C with a medium containing a high concentration of glucose (60 g/L). A maximum cell density of 5.78 g/L was obtained in the batch culture under hemin-stimulated respiration conditions, about three times as much as that achieved with anerobic homolactic fermentation (1.87 g/L) and aerobic heterolactic fermentation (1.80 g/L). The maximum specific growth rate was 0.60/h in hemin-stimulated respiration, slightly higher than that achieved in homolactic fermentation (0.56/h) and substantially higher than that in heterolactic fermentation (0.40/h). Alteration of metabolism caused by the supplementation of oxygen and hemin is evidenced by changes in both cell growth kinetics and metabolite formation kinetics, which are characterized by a unique pseudo-diauxic growth of L. lactis. We hypothesise that Lactococcus lactis generates bioenergy (ATP) through simultaneous lactate formation and hemin-stimulated respiration in the primary exponential phase, when glucose is abundant, and utilizes lactate for cell growth and cell maintenance in the stationary phase, after glucose is exhausted. We also examined the applicability of a modified logistic model and the Luedeking-Piret model for cell growth kinetics and metabolite formation kinetics, respectively.

Development of Chemically Defined Media Supporting High-Cell-Density Growth of Lactococci, Enterococci, and Streptococci

“…Besides the 19 grouped nutritional variables, two environmental parameters (temperature and starting pH) were also investigated. The original ranges of these two environmental variables were determined using data from previous studies (3,8,16).…”

“…In this study, the complex medium that was used for inoculum preparation and comparison with new CDMs was modified M17, in which 5 g/liter lactose was replaced by 20 g/liter glucose to support a higher level of growth (8). This complex medium (37.25 g/liter Difco M17 broth) was autoclaved for 20 min at 121°C before it was mixed with glucose that was sterilized separately.…”

“…cremoris (16). L. lactis has been granted generally recognized as safe status by the FDA and is used extensively in the dairy industry (2), among other industries (6,8,12). Recently, determination of the genome sequences of several L. lactis strains (2) has allowed development of metabolic models and enabled novel "omics" strategies to examine cellular metabolism during fermentation (1,8,11).…”

Using highly efficient nonlinear experimental design methods for optimization of Lactococcus lactis fermentation in chemically defined media

“…15 This complex medium (37.25 g/L Difco TM M17 Broth) was autoclaved for 20 min at 121 C before mixing with glucose that was sterilized separately.…”

“…[13][14][15][16] An existing complex medium, M17, 17 is used extensively to support the high cell density growth of L. lactis but often is unsuitable for studies in which a chemically defined medium (CDM) is required. 18 This would include studies in which specific metabolic or regulatory pathways are examined or in which variability due to complex ingredients is unacceptably high.…”