Abstract
The aim of this work was to physiologically characterize Erwinia chrysanthemi (strain 3937) cellulase (EGZ) secretion as a prelude to a more molecular analysis. First, we showed that EGZ secretion occurs in the late stage of logarithmic growth phase while no intracellular pool could be detected by immunotechniques. Second, the overproduction of EGZ led to a shift of its secretion towards the early stages of logarithmic growth phase, indicating that restriction of EGZ extracellular production to the late stage of growth is not due to some limitation in the cell secretion capacity. Third, the characterization of the outJ mutant (Ji, J., Hugouvieux-Cotte-Pattat, N. and Robert-Baudouy, J. (1989) Mol. Microbiol. 3, 285–293) showed that it is totally impaired in EGZ secretion even when EGZ is overproduced. Taken together, these observations indicated that EGZ secretion can be studied using multicopy plasmids and mid-exponential grown cells. Fourth, we showed that E. chrysanthemi EGZ cannot be secreted by E. carotovora (strain SCRI193) and that E. carotovora cellulase (CelV) cannot be secreted by E. chrysanthemi . These latter findings were unexpected in the context of the current trends of protein secretion in Gram-negative bacteria and suggest that, within each bacterial species, both the secretion machinery and the endogenous secreted enzymes co-evolved to gain a species-dependent specificity.
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