Papel de las actividades superóxido dismutasa y catalasa en la ...

RESULTS AND DISCUSSION
resist 100 mM of peroxide, a lethal concentration without peroxide pretreatment. In the
case of P. damselae subsp. piscicida, it is interesting to note that a significant increase
in survival rates of the non-virulent strain was observed when cultures were pulsed with
hydrogen peroxide compared to cells cultured until stationary phase. In contrast, this
increase has not been observed for the virulent strain, which always showed higher
survival regardless of the growth phase, or the pulse with hydrogen peroxide.
On the other hand, culture under iron-restricted conditions results in a significant
decrease in survival of both virulent and avirulent strains. The fact that this bacterial
species contains a ferric catalase (article 1.2., Article section), whose activity is reduced
under iron limiting conditions, may explain this result.
Superoxide dismutase and catalase are metalloenzymes that can possess different
metals in their active centre. Microorganisms capable to produce different superoxide
dismutase and catalase isoenzymes, depending on culture conditions, have been
described. These culture conditions include oxygen levels, low iron levels or growth
until stationary phase (Storz et al., 1990; Privalle and Fridovich, 1992; Crockford et al.,
1995; Schnell and Steinman, 1995; Barnes et al., 1996; Polack et al., 1996; St. John and
Steinman, 1996; Lynch and Kuramitsu, 2000; Yesilkaya et al., 2000; Geslin et al., 2001;
Vattanaviboon and Mongkolsuk, 2001).
Results obtained in the present work show that P. damselae subsp. piscicida does
not synthetize a new form of superoxide dismutase or catalase when cultured under
assayed conditions. Thus, all strains show only one band of superoxide dismutase
activity, with similar electrophoretic mobility to ferric superoxide dismutase described
by Barnes et al. (1999a). Even oxidative stress, by hydrogen peroxide or paraquat (an
oxygenic radical generator) addition, did not induce the synthesis of a different
isoenzyme, unlike CuZnSOD and MnSOD described in Escherichia coli (Hassan and
Fridovich, 1977; Privalle and Fridovich, 1992; Benov and Fridovich, 1994; Geslin et al.,
2001), MnSOD in A. salmonicida (Barnes et al., 1996; Barnes et al., 1999b),
Pseudomonas aeruginosa (Polack et al., 1996) and Streptococcus pneumoniae
(Yesilkaya et al., 2000). Neither restrictive iron conditions induce MnSOD synthesis
(Privalle and Fridovich, 1992; Barnes et al., 1999b). Although further studies would be
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