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Appl. Environ. Microbiol., Sep 1995, 3391-3399, Vol 61, No. 9
F Valence and S Lortal
The autolysins of Lactobacillus helveticus ISLC5 were detected and
partially characterized by renaturing sodium dodecyl sulfate
(SDS)-polyacrylamide gel electrophoresis with substrate-containing gels
(zymogram). By using lyophilized Micrococcus luteus cells or heated whole
cells of L. helveticus ISLC5 (0.2% [wt/vol]) as a substrate, several lytic
activities were detected in the whole-cell SDS extract of strain ISLC5 (i)
one activity at 42.4 kDa, which was named autolysin A, and (ii) six other
activities having very similar molecular weights (29.1, 29.6, 30, 30.8,
31.7, and 32.8 kDa), which were named autolysins B (B1 through B6,
respectively). As regards the temporal distribution of the enzymes,
autolysins A and B were detected in the cells harvested from the beginning
of the exponential growth phase. Autolysin A appeared to be associated only
with viable cells, whereas the autolysins B remained associated with the
cell envelope several days after the complete loss of culture viability.
When SDS-treated walls of L. helveticus ISLC5 were used as a substrate, a
supplementary lytic activity appeared at 37.5 kDa; it was considered a
peptidoglycan hydrolase, since it was not able to induce lysis of
whole-cell substrate. The autolysins of 30 other strains of L. helveticus
from various geographical origins were also analyzed by zymogram; all the
activity profiles obtained were similar to that of strain ISLC5 in terms of
the number of lytic bands and their apparent molecular weights. Only the
relative intensities of the lytic bands corresponding to autolysins A and B
were variable depending on the strains. This observation suggested that
autolysins are highly conserved enzymes. A concentrated crude lysate of the
virulent bacteriophage 832-B1 infecting L. helveticus was also analyzed by
zymogram; one lytic activity with an apparent molecular weight of 31.7 kDa,
very close to the weights of the autolysins B, was observed. Finally, the
autolysins of L. helveticus ISLC5 were successfully extracted from whole
cells by using a 1 M lithium chloride solution; they were partially
purified by precipitation, selective resolubilization, and gel filtration
chromatography, which led to a 20-fold increase in specific activity.
Copyright © 1995, American Society for Microbiology
Zymogram and Preliminary Characterization of Lactobacillus helveticus Autolysins
Laboratoire de Recherches de Technologie Laitiere, Institut National de la Recherche Agronomique, 35042 Rennes Cedex, France
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