Functional significance of a periplasmic Mn-superoxide dismutase from Aeromonas hydrophila.

AIMS

A better understanding of the role of superoxide dismutases (SODs) from Aeromonas hydrophila and particularly the Mn-SOD which shares a peculiar localization within the bacterial periplasm and is only detected during the stationary phase of growth.

METHODS AND RESULTS

A. hydrophila ATCC 7966 can express two distinct SODs: an Fe-SOD and an Mn-SOD. Using insertional mutagenesis, an Mn-SOD-deficient mutant was isolated. After growth of this mutant under conditions leading to the expression of an Mn-SOD, only the Fe-SOD could be detected in nondenaturing PAGE. Study of its response to the oxidative stress showed that the Mn-SOD was not implicated in the protection against intracellular superoxide but defended the bacterial cells against environmental superoxide.

CONCLUSIONS

By protecting the bacteria against external superoxide, the role of the Mn-SOD from A. hydrophila is equivalent to that of the Cu/Zn-SOD from the well-studied Escherichia coli.

SIGNIFICANCE AND IMPACT OF THE STUDY

The function of this Mn-SOD is in agreement with its periplasmic localization and may confer an advantage on the bacteria such as a virulence factor in cases of pathogenicity.