Affiliation:
1. AG Ökophysiologie, Max-Planck-Institut für Terrestrische Mikrobiologie, 35043 Marburg, Germany
Abstract
ABSTRACT
In the plant pathogen
Pseudomonas syringae
pv. glycinea PG4180 and other bacterial species, synthesis of the exopolysaccharide levan is catalyzed by the extracellular enzyme levansucrase. The results of Southern blotting and PCR analysis indicated the presence of three levansucrase-encoding genes in strain PG4180:
lscA
,
lscB
, and
lscC
. In this study,
lscB
and
lscC
were cloned from a genomic library of strain PG4180. Sequence analysis of the two
lsc
genes showed that they were virtually identical to each other and highly similar to the previously characterized
lscA
gene.
lscA
and
lscC
had a chromosomal location, whereas
lscB
resided on an indigenous plasmid of PG4180. Mutants with impaired expression of individual
lsc
genes and double mutants were generated by marker exchange mutagenesis. Determination of levansucrase activities in these mutants revealed that the
lscB
gene product was secreted but not that of
lscA
or
lscC
. Our results indicated that
lscB
and
lscC
but not
lscA
contributed to periplasmic levan synthesis of PG4180. The
lscB lscC
double mutant was completely defective in levan formation and could be complemented by either
lscB
or
lscC.
Our data suggested a compartment-specific localization of two
lsc
gene products, with LscB being the secreted, extracellular enzyme and LscC being the predominantly periplasmic levansucrase. Results of Western blot analyses indicated that
lscA
was not expressed and that
lscA
was not associated with levansucrase activities in any particular protein fraction. LscA could be detected in PG4180 only when transcribed from the vector-borne P
lac
promoter. PCR screening in various
P. syringae
strains with primers derived from the three characterized
lsc
genes demonstrated the presence of multiple Lsc isoenzymes in other
P. syringae
pathovars.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
47 articles.
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