Effects of metal ions on growth, β-oxidation system, and thioesterase activity of Lactococcus lactis

The effects of divalent metal ions (Ca2+, Mg2+, Fe2+, and Cu2+) on the growth, β-oxidation system, and thioesterase activity of Lactococcus lactis were investigated. Different metal ions significantly influenced the growth of L. lactis: Ca2+ and Fe2+ accelerated growth, whereas Cu2+ inhibited growth. Furthermore, Mg2+ inhibited growth of L. lactis at a low concentration but stimulated growth of L. lactis at a high concentration. The divalent metal ions had significant effects on activity of the 4 key enzymes of the β-oxidation system (acyl-CoA dehydrogenase, enoyl-CoA hydratase, L-3-hydroxyacyl-CoA dehydrogenase, and thiolase) and thioesterase of L. lactis. The activity of acyl-CoA dehydrogenases increased markedly in the presence of Ca2+ and Mg2+, whereas it decreased with 1 mmol/L Fe2+ or 12 mmol/L Mg2+. All the metal ions could induce activity of enoyl-CoA hydratase. In addition, 12 mmol/L Mg2+ significantly stimulated activity of L-3-hydroxyacyl-CoA dehydrogenase, and all metal ions could induce activity of thiolase, although thiolase activity decreased significantly when 0.05 mmol/L Cu2+ was added into M17 broth. Inhibition of thioesterase activity by all 4 metal ions could be reversed by 2 mmol/L Ca2+. These results help us understand the effect of metal ions on the β-oxidation system and thioesterase activity of Lactococcus lactis.