Document Detail

The ++Sinorhizobium meliloti lon protease is involved in regulating exopolysaccharide synthesis and is required for nodulation of alfalfa.
MedLine Citation:
PMID:  10762258     Owner:  NLM     Status:  MEDLINE    
While screening for Sinorhizobium meliloti Pho regulatory mutants, a transposon mutant was isolated that constitutively expressed higher levels of acid and alkaline phosphatase enzymes. This mutant was also found to form pseudonodules on alfalfa that were delayed in appearance relative to those formed by the wild-type strain, it contained few bacteroids, and it did not fix nitrogen. Sequence analysis of the transposon insertion site revealed the affected gene to have high homology to Lon proteases from a number of organisms. In minimal succinate medium, the mutant strain was found to grow more slowly, reach lower maximal optical density, and produce more extracellular polysaccharide (EPS) than the wild-type strain. The mutant fluoresced brightly on minimal succinate agar containing calcofluor (which binds to EPSI, a constitutively expressed succinoglycan), and gas chromotographic analysis of purified total EPS showed that the glucose-to-galactose ratio in the lon mutant total EPS was 5.0 +/- 0.2 (mean +/- standard error), whereas the glucose-to-galactose ratio in the wild-type strain was 7.1 +/- 0.5. These data suggested that in addition to EPSI, the lon mutant also constitutively synthesized EPSII, a galactoglucan which is the second major EPS known to be produced by S. meliloti, but typically is expressed only under conditions of phosphate limitation. (13)C nuclear magnetic resonance analysis showed no major differences between EPS purified from the mutant and wild-type strains. Normal growth, EPS production, and the symbiotic phenotype were restored in the mutant strain when the wild-type lon gene was present in trans. The results of this study suggest that the S. meliloti Lon protease is important for controlling turnover of a constitutively expressed protein(s) that, when unregulated, disrupts normal nodule formation and normal growth.
M L Summers; L M Botero; S C Busse; T R McDermott
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Journal of bacteriology     Volume:  182     ISSN:  0021-9193     ISO Abbreviation:  J. Bacteriol.     Publication Date:  2000 May 
Date Detail:
Created Date:  2000-06-13     Completed Date:  2000-06-13     Revised Date:  2013-04-18    
Medline Journal Info:
Nlm Unique ID:  2985120R     Medline TA:  J Bacteriol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2551-8     Citation Subset:  IM    
Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana 59717, USA.
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MeSH Terms
ATP-Dependent Proteases
Adenosine Triphosphatases / genetics,  metabolism*
Base Sequence
DNA, Bacterial
Heat-Shock Proteins / genetics,  metabolism*
Medicago sativa / growth & development
Molecular Sequence Data
Polysaccharides / biosynthesis*
Serine Endopeptidases / genetics,  metabolism*
Sinorhizobium meliloti / enzymology*,  genetics,  growth & development
Reg. No./Substance:
0/DNA, Bacterial; 0/Heat-Shock Proteins; 0/Polysaccharides; EC 3.4.21.-/ATP-Dependent Proteases; EC 3.4.21.-/Serine Endopeptidases; EC 3.6.1.-/Adenosine Triphosphatases

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