Improvement of the respiration efficiency of <Emphasis Type="Italic">Lactococcus lactis</Emphasis> by decreasing the culture pH

Objective

The growth characteristics and intracellular hemin concentrations of Lactococcus lactis grown under different culture pH and aeration conditions were examined to investigate the effect of culture pH on the respiration efficiency of L. lactis NZ9000 (pZN8148).

Results

Cell biomass and biomass yield of L. lactis grown with 4 μg hemin/ml and O₂ were higher than those without aeration when the culture pH was controlled at 5–6.5. The culture pH affected the respiratory efficiency in the following order of pH: 5 > 5.5 > 6 > 6.5; the lag phase increased as the culture pH decreased. Hemin accumulation was sensitive to culture pH. Among the four pH conditions, pH 5.5 was optimal for hemin accumulation in the cells. The highest intracellular hemin level in L. lactis resting cells incubated at different pH saline levels (5–6.5) was at pH 5.5.

Conclusion

The respiration efficiency of L. lactis under respiration-permissive conditions increases markedly as the culture pH decreases. These results may help develop high cell-density L. lactis cultures. Thus, this microorganism may be used for industrial applications.