Affiliation:
1. Department of Bacteriology, Microbiology and Tumorbiology Center, Karolinska Institutet, S-17177 Stockholm, Sweden,1 and
2. Max-Planck-Institut für Experimentelle Endokrinologie, D-30603 Hannover, Germany2
Abstract
ABSTRACT
Mouse-virulent
Salmonella typhimurium
strains SR-11 and ATCC 14028-1s express curli fibers, thin aggregative fibers, at ambient temperature on plates as judged by Western blot analysis and electron microscopy. Concomitantly with curli expression, cells develop a rough and dry colony morphology and bind the dye Congo red (called the rdar morphotype). Cloning and characterization of the two divergently transcribed operons required for curli biogenesis,
csgBA(C)
and
csgDEFG
, from
S. typhimurium
SR-11 revealed the same gene order and flanking genes as in
Escherichia coli
. The divergence of the curli region between
S. typhimurium
and
E. coli
at the nucleotide level is above average (22.4%). However, a high level of conservation at the protein level, which ranged from 86% amino acid homology for the fiber subunit CsgA to 99% homology for the lipoprotein CsgG, implies functional constraints on the gene products. Consequently,
S. typhimurium
genes on low-copy-number plasmids were able to complement respective
E. coli
mutants, although not always to wild-type levels.
rpoS
and
ompR
are required for transcriptional activation of (at least) the
csgD
promoter. The high degree of conservation at the protein level and the identical regulation patterns in
E. coli
and
S. typhimurium
suggest similar roles of curli fibers in the same ecological niche in the two species.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
373 articles.
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