Isolation of succinate dehydrogenase from Desulfobulbus elongatus, a propionate oxidizing, sulfate reducing bacterium.

Succinate dehydrogenase was purified from the particulate fraction of Desulfobulbus. The enzyme catalyzed both fumarate reduction and succinate oxidation but the rate of fumarate reduction was 8-times less than that of succinate oxidation. Quantitative analysis showed the presence of 1 mol of covalently bound flavin and 1 mol of cytochrome b per mol of succinate dehydrogenase. The enzyme contained three subunits with molecular mass 68.5, 27.5 and 22 kDa. EPR spectroscopy indicated the presence of at least two iron sulfur clusters. 2-Heptyl-4-hydroxy-quinoline-N-oxide inhibited the electron-transfer between succinate dehydrogenase and a high redox potential cytochrome c3 from Desulfobulbus elongatus.

Fermentation of citrate by Lactobacillus plantarum in the presence of a yeast under acid conditions.

At pH 3.6, Lactobacillus plantarum is unable to grow on citrate or to ferment it in the absence of another carbon source such as glucose. In a defined medium containing glucose and citrate, with a higher concentration of the former than the latter, as in many fermented alcoholic beverages, L. plantarum will first ferment the sugar. The production of lactate from glucose degradation increases the acidity of the medium and inhibits the fermentation of citrate. In co-culture with Saccharomyces cerevisiae, part of the glucose is fermented by the yeast, partly avoiding the pH drop and the inhibition of citrate fermentation by L. plantarum. Fermentation was still possible at pH values around 3.0.

Ethylene regulation of carotenoid accumulation and carotenogenic gene expression in colour-contrasted apricot varieties (Prunus armeniaca).

In order to elucidate the regulation mechanisms of carotenoid biosynthesis in apricot fruit (Prunus armeniaca), carotenoid content and carotenogenic gene expression were analysed as a function of ethylene production in two colour-contrasted apricot varieties. Fruits from Goldrich (GO) were orange, while Moniqui (MO) fruits were white. Biochemical analysis showed that GO accumulated precursors of the uncoloured carotenoids, phytoene and phytofluene, and the coloured carotenoid, beta-carotene, while Moniqui (MO) fruits only accumulated phytoene and phytofluene but no beta-carotene. Physiological analysis showed that ethylene production was clearly weaker in GO than in MO. Carotenogenic gene expression (Psy-1, Pds, and Zds) and carotenoid accumulation were measured with respect to ethylene production which is initiated in mature green fruits at the onset of the climacteric stage or following exo-ethylene or ethylene-receptor inhibitor (1-MCP) treatments. Results showed (i) systematically stronger expression of carotenogenic genes in white than in orange fruits, even for the Zds gene involved in beta-carotene synthesis that is undetectable in MO fruits, (ii) ethylene-induction of Psy-1 and Pds gene expression and the corresponding product accumulation, (iii) Zds gene expression and beta-carotene production independent of ethylene. The different results obtained at physiological, biochemical, and molecular levels revealed the complex regulation of carotenoid biosynthesis in apricots and led to suggestions regarding some possible ways to regulate it.

Influence of calcium addition on growth of highly purified syntrophic cultures degrading long-chain Fatty acids.

Two highly purified syntrophic associations resulting in acetogenesis from stearate (SM) and oleate (OM) were obtained from the sludges of a sewage digestor. In both cases, Methanospirillum hungatei together with short, motile, gram-negative, nonfluorescent rods morphologically similar to Syntrophomonas wolfei were identified by microscopic examination. Besides growing on volatile fatty acids (butyrate through caproate), both cultures grew on oleate (C(18:1)) and numerous even-numbered, saturated long-chain fatty acids (LCFA [decanoate through stearate]). In addition, during growth on LCFA, supplementation of the culture media with calcium chloride was an absolute requirement. The sole difference between the associations was observed when SM and OM cultures were transferred from a stearate to an oleate medium. The SM culture needed 10 days before starting to degrade oleate, whereas the OM culture grew immediately, but the OM culture also grew immediately when transferred to stearate medium. Saturated LCFA degradation occurred in the presence of equinormal amounts of calcium (fatty acid/Ca ratio, 2). On the other hand, OM degradation only took place in the presence of an equimolar amount of calcium (fatty acid/Ca ratio, 1). These observations are discussed by considering the solubility constants of LCFA as calcium salts and the toxicity of the free acids against microorganisms.

[Interaction among anaerobic microbe species in the rumen]. / Interactions entre espèces microbiennes anaérobies dans le rumen.

The rumen is a strictly anaerobic ecosystem colonized by an extremely dense microflora and microfauna. These populations are composed of a grand variety of bacterial and protozoal species. Their cohabitation allows observation of most of the known stages of communal life. The different hydrolytic, fermentative and methanogenic activities of these populations ensure the efficient degradation of cell wall constituent in forages (cellulose, hemicellulose, pectin) ingested by ruminants.

Homoacetogenic Fermentation of Cellulose by a Coculture of Clostridium thermocellum and Acetogenium kivui.

Interrelationships between methanogens and fermentative or hydrolytic bacteria are well documented; however, such cocultures do not allow a complete fermentation shift to a peculiar metabolite. We describe here a new stable association between Clostridium thermocellum and Acetogenium kivui which converts 1 mol of cellulose (anhydroglucose equivalent) into 2.7 mol of acetate.

Trophic relationships between Saccharomyces cerevisiae and Lactobacillus plantarum and their metabolism of glucose and citrate.

Glucose and citrate are two major carbon sources in fruits or fruit juices such as orange juice. Their metabolism and the microorganisms involved in their degradation were studied by inoculating with an aliquot of fermented orange juice a synthetic model medium containing glucose and citrate. At pH 3.6, their degradation led, first, to the formation of ethanol due to the activity of yeasts fermenting glucose and, eventually, to the formation of acetate resulting from the activity of lactobacilli. The yeast population always outcompeted the lactobacilli even when the fermented orange juice used as inoculum was mixed with fermented beet leaves containing a wider variety of lactic acid bacteria. The evolution of the medium remained similar between pH 3.3 and 5.0. At pH 3.0 or below, the fermentation of citrate was totally inhibited. Saccharomyces cerevisiae and Lactobacillus plantarum were identified as the only dominant microorganisms. The evolution of the model medium with the complex microbial community was successfully reconstituted with a defined coculture of S. cerevisiae and L. plantarum. The study of the fermentation of the defined model medium with a reconstituted microbial community allows us to better understand the behavior not only of fermented orange juice but also of many other fruit fermentations utilized for the production of alcoholic beverages.

Reductive carboxylation of propionate to butyrate in methanogenic ecosystems.

During the batch degradation of sodium propionate by the anaerobic sludge from an industrial digestor, we observed a significant amount of butyrate formation. Varying the initial propionate concentrations did not alter the ratio of maximal butyrate accumulation to initial propionate concentration within a large range. By measuring the decrease in the radioactivity of [1-C]butyrate during propionate degradation, we estimated that about 20% of the propionate was converted to butyrate. Labeled butyrate was formed from [1-C]propionate with the same specific radioactivity, suggesting a possible direct pathway from propionate to butyrate. We confirmed this hypothesis by nuclear magnetic resonance studies with [C]propionate. The results showed that [1-C]-, [2-C]-, and [3-C]propionate were converted to [2-C]-, [3-C]-, and [4-C]butyrate, respectively, demonstrating the direct carboxylation on the carboxyl group of propionate without randomization of the other two carbons. In addition, we observed an exchange reaction between C-2 and C-3 of the propionate, indicating that acetogensis may proceed through a randomizing pathway. The physiological significance and importance of various metabolic pathways involved in propionate degradation are discussed, and an unusual pathway of butyrate synthesis is proposed.

Clostridium neopropionicum sp. nov., a strict anaerobic bacterium fermenting ethanol to propionate through acrylate pathway.

Strain X4 was isolated several years ago from an anaerobic mesophilic plant treating vegetable cannery waste waters. It was the first example of propionic fermentation from ethanol. Morphologic and physiologic characterizations of the strain are presented here. This strain is described as type strain of a new species, Clostridium neopropionicum sp. nov. Whole cells of strain X4 ferment [1-13C] ethanol and CO2 to [2-13C] propionate, [1-13C] acetate and [2-13C] propanol, suggesting the absence of a randomizing pathway during the propionate formation. Enzymes involved in this fermentation were assayed in cell-free extracts of cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase, phosphate acetyl transferase, acetate kinase, pyruvate synthase, lactate dehydrogenases, and the enzymes of the acrylate pathway were detected at activities sufficient to be involved in ethanol fermentation. The same pathway may be used for the degradation of lactate or acrylate to acetate.