Pre-cold stress increases acid stress resistance and induces amino acid homeostasis in Lactococcus lactis NZ9000
Purpose: To investigate the effects of pre-cold stress treatments on subsequent acid stress resistance and the viability of Lactococcus lactis during acid fermentation.
Methods: Bacterial strains were grown at 4 °C for 2 h pre-adaptation, and then subjected to various stresses including exposure to 4 °C, 1 mM hydrogen peroxide, 5 % sodium chloride, 7 % ethanol, and lactic acid (pH 5.5) to determine if any of these stress treatments could increase acid stress resistance and induce amino acid homeostasis during acid fermentation.
Results: Among the different abiotic stresses investigated, pre-adaptation of lag-phase cultures to cold shock significantly enhanced cell survival during subsequent acid stress. The stress profile of L. lactis pre-adapted to cold stress revealed induction of amino acid homeostasis and energy balance; however, pre-adaptation responses are induced upon exposure to acid stress alone. Compared to exposure to acid stress only, pre-adaptation to cold stress decreased the redox balance ratio and the formation of hydroxyl radicals, indicating a change in aerobic respiration and oxidative state of the bacteria.
Conclusion: Pre-adaptation to cold stress rescued L. lactis from the deleterious effects of subsequent acid exposure by modifying the amino acid metabolic pathway, leading to an improvement in redox mobility of acid stress response.
Keywords: Pre-cold stress, Acis stress resistance, Lactococcus lactis, Redox balance, Amino acid homeostasis