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Applied and Environmental Microbiology, July 1999, p. 2833-2840, Vol. 65, No. 7
Department of Biological Sciences, University
of Calgary, Calgary, Alberta, Canada
Received 19 November 1998/Accepted 20 April 1999
A 3-kb region containing the determinant for bacteriocin activity
from Rhizobium leguminosarum 248 was isolated and
characterized by Tn5 insertional mutagenesis and DNA
sequencing. Southern hybridizations showed that this bacteriocin was
encoded on the plasmid pRL1JI and that homologous loci were not found
in other unrelated R. leguminosarum strains.
Tn5 insertional mutagenesis showed that mutations in the
C-terminal half of the bacteriocin open reading frame apparently did
not abolish bacteriocin activity. Analysis of the deduced amino acid
sequence revealed that, similarly to RTX proteins (such as hemolysin
and leukotoxin), this protein contains a characteristic nonapeptide
repeated up to 18 times within the protein. In addition, a novel 19- to
25-amino-acid motif that occurred every 130 amino acids was detected.
Bacteriocin bioactivity was correlated with the presence of a protein
of approximately 100 kDa in the culture supernatants, and the
bacteriocin bioactivity demonstrated a calcium dependence in both
R. leguminosarum and Sinorhizobium meliloti. A
mutant of strain 248 unable to produce this bacteriocin was found to
have a statistically significant reduction in competitiveness for
nodule occupancy compared to two test strains in coinoculation assays.
However, this strain was unable to compete any more successfully with a
third test strain, 3841, than was wild-type 248.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Cloning and Characterization of a Rhizobium
leguminosarum Gene Encoding a Bacteriocin with Similarities to
RTX Toxins
*
Corresponding author. Mailing address: Department of
Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada. Phone: (403) 220-8473. Fax: (403) 289-9311. E-mail:
hynes{at}acs.ucalgary.ca.
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