Microcalorimetric study of the effect of manganese on the growth and metabolism in a heterogeneously expressing manganese-dependent superoxide dismutase (Mn-SOD) strain

Abstract

In bacteria, manganese (Mn) is best understood for its roles in protection against oxidative stress as a cofactor of manganese-dependent superoxide dismutase (Mn-SOD). There are four SOD enzymes, including two distinct Mn-SOD proteins (SodA1 and SodA2), with an approximately 53% amino sequence identity to each other, one Cu/Zn-SOD and one Fe-SOD in Bacillus thuringiensis. The specific activity of heterogeneously expressed SodA1 enzyme in Escherichia coli was 10,860 U mg−1, which was enhanced with the addition of elevated exogenous Mn(II) levels and reached the highest specific activity (14,519 U mg−1) at 80 μM Mn(II). However, neither the purified SodA1 enzyme nor the E. coli recombinant strain BL21-SOD could oxidize Mn(II) in vitro or in vivo. The growth of BL21-SOD strain was also increased by 2 mM Mn(II), and its intracellular accumulated Mn(II) level reached 41.5 μM. The obtained power–time curves from microcalorimetric assay demonstrated that Q peak of BL21-SOD cultivated with 2 mM Mn(II) was significantly increased, which was 3.55-fold and 3.85-fold higher than the parent strain BL21(DE3) and control strain BL21-pET, respectively, indicating that the exposure of Mn(II) and accompanying oxidative stress might induce and activate the overproduction of SodA1 to eliminate toxic O 2 − .