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Appl. Environ. Microbiol., May 1995, 1959-1967, Vol 61, No. 5
A Chatterjee, Y Cui, Y Liu, CK Dumenyo and AK Chatterjee
The soft-rotting bacterium, Erwinia carotovora subsp. carotovora 71,
produces extracellular enzymes such as pectate lyase isozymes (Pels),
cellulase (Cel), polygalacturonase (Peh), and protease (Prt). While the
extracellular levels of these enzymes are extremely low when the bacterium
is grown in salts-yeast extract-glycerol (SYG) medium, the enzymatic
activities are highly induced in SYG medium supplemented with celery
extract. By transposon (mini-Tn5) mutagenesis, we isolated a RsmA- mutant,
AC5070, which overproduces extracellular enzymes; the basal levels of Pel,
Peh, and Cel in AC5070 are higher than the induced levels in the RsmA+
parent, AC5047. While Peh production is mostly constitutive in AC5070, Pel,
Cel, and Prt production is still inducible with celery extract. The high
basal levels of pel-1, pel-3, and peh-1 mRNAs in AC5070 demonstrate that
overproduction of the pectolytic enzymes is due to the stimulation of
transcription. Using chromosomal DNA flanking mini-Tn5 as a probe, we
cloned the wild-type rsmA+ allele, which suppresses Pel, Peh, Cel, and Prt
production in both RsmA+ and RsmA- strains. The RsmA- mutant, like its
parent, produces N-(3- oxohexanoyl)-L-homoserine lactone (HSL), a
starvation/cell density- sensing signal required for extracellular enzyme
production. To examine the role of HSL, we constructed HSL-deficient
strains by replacing hslI, a locus required for HSL production, with
hslI::Tn3HoHo1-Spc. While the basal levels of Pel, Peh, Cel, and Prt are
comparable in the RsmA- mutant and its HSL- derivative, these enzymes are
barely detectable in the Hsl- derivative of the RsmA+ parent
strain.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Inactivation of rsmA leads to overproduction of extracellular pectinases, cellulases, and proteases in Erwinia carotovora subsp. carotovora in the absence of the starvation/cell density-sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone
Department of Plant Pathology, University of Missouri, Columbia 65211, USA.
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