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J Courtois

Publications and source records attributed to J Courtois.

At least 37 records · Page 2Linked to original sources
PubMed1997

Mechanism of gluconate synthesis in Rhizobium meliloti by using in vivo NMR.

The dehydrogenation of [1-(13)C]- and [2-(13)C]glucose into gluconate was monitored by NMR spectroscopy in living cell suspensions of two Rhizobium meliloti strains. The synthesis of gluconate was accompanied, in the cellular environment, by the formation of two gluconolactones, a gamma-lactone being detected in addition to the expected delta-lactone. These lactones--as well as the gluconate--could be further metabolized by the cells. The delta-lactone was utilized faster than the gamma-lactone. The presence--in significant amounts--and the relative stability of the lactones raise the question of their possible physiological significance.

Alkalies↗
PubMed1997

Identification of glucuronan lyase from a mutant strain of Rhizobium meliloti.

The Rhizobium meliloti M5N1CS (NCIMB 40472) mutant strain wich induces nodule formation on alfalfa roots, produces a (1 --> 4)-beta-D-glucuronan partially acetylated. During fermentation under specific conditions, the molecular weight of the polymer decrease, the presence of polysaccharide degrading enzyme was suspected. A glucuronan lyase was identified, this new bacterial lyase produces d.p. 4 oligoglucuronans, substituents (acetates) present on the substrate reduced the enzyme activity.

Acetylation↗
PubMed1997

Exopolysaccharide and Poly-(beta)-Hydroxybutyrate Coproduction in Two Rhizobium meliloti Strains.

The effects of different nitrogen and carbon sources on cell growth, pH, and exopolysaccharide (EPS) and poly-(beta)-hydroxybutyrate (PHB) production by two strains of Rhizobium meliloti (M5N1 and Su47) are reported. Differences in the behavior of glucose- and fructose-grown cells were shown, in particular with the M5N1 strain. Growth in a glucose-containing medium was accompanied by acidification of the culture medium, which leads to cell death. On fructose, acidification was detected only in the medium with a mineral nitrogen supply. A lag phase in EPS production was observed with cells grown with glucose, probably related to an initial extracellular conversion of the carbohydrate into an acid. No lag phase was observed in EPS production from fructose or in PHB synthesis whatever the carbon source. A decrease in PHB content was noticed for both strains under conditions where acidification of media occurred. The extent of production, emphasized by the use of a coproduction index, indicates that the M5N1 strain is a more promising organism than is the Su47 strain for polymer production. Such a strain, put in rich medium (containing yeast extract) supplemented with fructose, accumulated PHB up to 85% of dry cell weight and excreted about 1.5 g of EPS per liter in the medium. Regulation of the coproduction of EPS and PHB by these cells is suggested.

Journal Article↗
PubMed1997

[Temporomandibular joint problems in assessment].

Manifestations of function disorders of the temporomandibular joint may have the same expression whether their origin is a natural cause or trauma. It is not always possible to make a scientifically valid distinction between a consequence of external trauma and internal cause(s). Often, the only reasonable attitude is to state that a transitive aggravation of the former status has occurred after trauma.

Expert Testimony↗
PubMed1995

Study of parameters affecting poly(3-hydroxybutyrate) quantification by gas chromatography.

Poly(3-hydroxybutyrate) (PHB) quantification has been developed mostly using acidic methanolysis followed by GC analysis of the 3-hydroxybutyrate methyl ester. However, under our experimental conditions, only 62% of the ester was detected by GC analysis. Following the study of the different steps involved in this method (i.e., hydrolysis, esterification, and recovery of the ester), the recovery was shown to be limiting. Addition of water to the organic phase, required for its purification before injection, led to the partition of the ester between the organic and the aqueous phase. The influence of the length of acidic methanolysis time on the amount of ester detected was also investigated. NMR analysis was used to show that secondary products were absent in both phases, regardless of heating time. Moreover, increasing acid concentration and the use of lyophilized cells were shown to lead to the decrease of the treatment time. Concerning internal standard choice, methyl benzoate was found to meet all the requirements to correct injection volume errors or to follow organic phase volume changes as a function of acid and water concentrations. The validity of the method was checked on Rhizobium meliloti M5N1 cells, which are shown to produce about 60% PHB (w/w) when cultivated with fructose as the carbon source.

Chromatography, Gas↗
PubMed1995

Effects of salts on production and on O-acetylation of glucuronan excreted by the Rhizobium meliloti M5N1 CS strain.

Acetylation determined by 1H-nuclear magnetic resonance spectroscopy and production of the glucuronan excreted by the Rhizobium meliloti M5N1CS strain during cultivation in RCS medium with and without added magnesium salts have been studied. These salts induce an increase in the degree of substitution and the molar ratio of 2,3-di-O-acetyl residues. A decrease in production is observed after 75 h of fermentation as the magnesium salt concentration increases. The presence of manganese and sodium salts in the culture induces inhibition of exopolysaccharide (EPS) production. However, the structure of the EPS is similar to that of the EPS produced by standard fermentation, without modification in the degree of substitution.

Acetylation↗
PubMed1995

Cyclic (1-->2)-beta-D-glucans excreted by the glucuronan-producing strain Rhizobium meliloti M5N1CS (NCIMB 40472) and by the succinoglycan-producing strain Rhizobium meliloti M5N1.

During fermentation, the mutant strain Rhizobium meliloti M5N1CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1-->4)-beta-D-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1-->2)-beta-D-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases.

Acetylation↗
PubMed1994

Physicochemical properties of extracellular (1-->4)-beta-D-glucuronan produced by the Rhizobium meliloti M5N1CS strain during fermentation: evidence of degradation by an exoenzyme activated by Mg2+.

The mutant Rhizobium meliloti M5N1CS (NCIMB 40472) produced a partially acetylated (1-->4)-beta-D-glucuronan during fermentation. The polysaccharide (EPS) extracted from broth during fermentation by microfiltration and ultrafiltration (using a 100 kDa cut-off membrane) was characterized by size exclusion chromatography. The weight-average molecular weight (Mw) of the EPS decreased from 7.5 x 10(5) to 5 x 10(5) between 27 and 75 h of fermentation. When MgSO4.7H2O (0.8 gl-1 per day) was present in the medium during the same period, the Mw of the EPS decreased to 1.5 x 10(5). Since EPS degradation was detected after microfiltration of the fermentation medium supplemented with magnesium, the Mw decrease of the EPS extracted during fermentation may be explained by enzymic degradation of the polymer activated by Mg2+ ions.

Bacterial Proteins↗