Biomedical subjects

R Moletta

Publications and source records attributed to R Moletta.

46 records · Page 3Linked to original sources

PubMed1998

Influence of biomass accumulation on bed expansion characteristics of a down-flow anaerobic fluidized-bed reactor.

This article describes the bed expansion characteristics of a down-flow anaerobic fluidized bed reactor treating a synthetic wastewater. Experiments were carried out in a 0.08 m diameter and 1 m length PVC column. The carrier used was ground perlite (an expanded volcanic rock). Particles characteristics were 0.968 mm in diameter, specific density of 213 kg x m-3 and Umf (minimal fluidization velocity): 2.3 m x h-1. Experimental data of terminal velocities and bed expansion parameters at several biofilm thicknesses were compared to different models predicting the bed expansion of up-flow and down-flow fluidized beds. Measured bed porosities at different liquid superficial velocities for the different biofilm thicknesses were in agreement with the Richardson-Zaki model, when Ut (particle terminal velocity) and n (expansion coefficient) were calculated by linear regression of the experimental data. Terminal velocities of particles at different biofilm thicknesses calculated from experimental bed expansion data, were found to be much smaller than those obtained when Cd (drag coefficient) is determined from the standard drag curve (Lapple and Sheperd, 1940) or with others' correlations (Karamanev and Nikolov, 1992a,b). This difference could be explained by the fact that free-rising particles do not obey Newton's law for free-settling, as proposed by Karamanev and Nikolov (1992a,b) and Karamanev et al. (1996). In the present study, the same free-rising behavior was observed for all particles (densities between 213 and 490 kg x m-3).

Anaerobiosis↗

PubMed1998

16S rDNA sequence diversity of a culture-accessible part of an anaerobic digestor bacterial community.

A bacterial culture-based inventory with 16S rDNA identification of the isolates was carried out on an anaerobic digestor microbial ecosystem to compare to the 16S rDNA sequences directly retrieved from the ecosystem by a molecular inventory previously made in our laboratory. Twenty OTUs (Operational Taxonomic Units) belonging to five of the major bacterial groups were identified from 338 isolated colonies. The sequences of 13 of the 20 OTUs were not closely related to any hitherto published sequences (less than 96% sequence identity). Six OTUs out of 20 were found to have sequences similar to sequences of the molecular inventory. Despite the biases expected to be associated with the molecular and culture-based methods, the distribution of the isolated OTUs into the different bacterial phyla was similar to that of the molecular OTUs.

Journal Article↗

PubMed1998

Microvirgula aerodenitrificans gen. nov., sp. nov., a new gram-negative bacterium exhibiting co-respiration of oxygen and nitrogen oxides up to oxygen-saturated conditions.

A denitrifier micro-organism was isolated from an upflow denitrifying filter inoculated with an activated sludge. The cells were Gram-negative, catalase- and oxidase-positive curved rods and very motile. They were aerobic as well as anoxic heterotrophs that had an atypical respiratory type of metabolism in which oxygen and nitrogen oxides were used simultaneously as terminal electron acceptors. The G&C content was 65 mol%. Our isolate was phenotypically similar to Comamonas testosteroni, according to classical systematic classification systems. However, a phylogenetic analysis based on the 165 rRNA sequence showed that the aerobic denitrifier could not be assigned to any currently recognized genus. For these reasons a new genus and species, Microvirgula aerodenitrificans gen. nov., sp. nov., is proposed, for which SGLY2T is the type strain.

Base Sequence↗

PubMed1997

Relationship between effect of ethanol on proton flux across plasma membrane and ethanol tolerance, in Pichia stipitis.

Pichia stipitis efficiently converts glucose or xylose into ethanol but is inhibited by ethanol concentrations exceeding 30 g/L. In Saccharomyces cerevisiae, ethanol has been shown to alter the movement of protons into and out of the cell. In P. stipitis the passive entry of protons into either glucose- or xylose-grown cells is unaffected at physiological ethanol concentrations. In contrast, active proton extrusion is affected differentially by ethanol, depending on the carbon source catabolized. In fact, in glucose-grown cells, the H(+)-extrusion rate is reduced by low ethanol concentrations, whereas, in xylose-grown cells, the H(+)-extrusion rate is reduced only at non-physiological ethanol concentrations. Thus, the ethanol inhibitory effect on growth and ethanol production, in glucose-grown cells, is probably caused by a reduction in H(+)-extrusion. Comparison of the rates of H(+)-flux with the related in vitro H(+)-ATPase activity suggests a new mechanism for the regulation of the proton pumping plasma membrane ATPase (EC 3.6.1.3) of P. stipitis, by both glucose and ethanol. Glucose activates both the ATP hydrolysis and the proton-pumping activities of the H(+)-ATPase, whereas ethanol causes an uncoupling between the ATP hydrolysis and the proton-pumping activities. This uncoupling may well be the cause of ethanol induced growth inhibition of glucose grown P. stipitis cells.

Journal Article↗

PubMed1997

Phosphate Release and Uptake by Pure Cultures of Acinetobacter sp.: Effect of the Volatile Fatty Acids Concentration

Phosphorus release and uptake by pure cultures of Acinetobacter strains were investigated under anaerobic and aerobic conditions respectively. Tests were performed to study the relationship between phosphorus release-storage reaction and behavior of extracellular organic substrates: acetic, propionic, and butyric acids have been used at four concentrations (50, 100, 500, and 1000 mg · L-1) in the anaerobic step of biological phosphorus removal. The results obtained depend on the strain and the volatile fatty acid (VFA) used. Phosphorus released under anaerobic condition was not always related to the amount of VFA or phosphorus consumed. Phosphorus uptake (P-uptake) in the aerobic step was found to be independent of phosphorus release rates. The best phosphorus uptake rates were obtained by Acinetobacter lwoffi ATCC21130 and Acinetobacter calcoaceticus Genoespecie SUCT-5 with butyric acid as carbon source.

Journal Article↗

PubMed1997

Molecular microbial diversity of an anaerobic digestor as determined by small-subunit rDNA sequence analysis.

The bacterial community structure of a fluidized-bed reactor fed by vinasses (wine distillation waste) was analyzed. After PCR amplification, four small-subunit (SSU) rDNA clone libraries of Bacteria, Archaea, Procarya, and Eucarya populations were established. The community structure was determined by operational taxonomic unit (OTU) phylogenetic analyses of 579 partial rDNA sequences (about 500 bp long). A total of 146 OTUs were found, comprising 133, 6, and 7 from the Bacteria, Archaea, and Eucarya domains, respectively. A total of 117 bacterial OTU were affiliated with major phyla: low-G+C gram-positive bacteria, Cytophaga-Flexibacter-Bacteroides, Proteobacteria, high-G+C gram-positive bacteria, and Spirochaetes, where the clone distribution was 34, 26, 17, 6, and 4%, respectively. The other 16 bacterial OTUs represent 13% of the clones. They were either affiliated with narrow phyla such as Planctomyces-Chlamydia, green nonsulfur bacteria, or Synergistes, or deeply branched on the phylogenetic tree. A large number of bacterial OTUs are not closely related to any other hitherto determined sequences. The most frequent bacterial OTUs represents less than 5% of the total bacterial SSU rDNA sequences. However, the 20 more frequent bacterial OTUs describe at least 50% of these sequences. Three of the six Archaea OTUs correspond to 95% of the Archaea population and are very similar to already known methanogenic species: Methanosarcina barkeri, Methanosarcina frisius, and Methanobacterium formicicum. In contrast, the three other Archaea OTUs are unusual and are related to thermophilic microorganisms such as Crenarchaea or Thermoplasma spp. Five percent of the sequences analyzed were chimeras and were removed from the analysis.

Bacteria, Anaerobic↗

PubMed1992

Alcoholic glucose and xylose fermentations by the coculture process: compatibility and typing of associated strains.

As part of the simultaneous fermentation of both glucose and xylose to ethanol by a coculture process, compatibilities between xylose-fermenting yeasts and glucose-fermenting species were investigated. Among the Saccharomyces species tested, none inhibited growth of the xylose-fermenting yeasts. By contrast, many xylose-fermenting yeasts, among the 11 tested, exerted an inhibitory effect on growth of the selected Saccharomyces species. Killer character was demonstrated in three strains of Pichia stipitis. Such strains, despite their high fermentative performances, cannot be used to ferment D-xylose in association with the selected Saccharomyces species. From compatibility tests between xylose-fermenting yeasts and Saccharomyces species, pairs of microorganisms suitable for simultaneous xylose and glucose fermentations by coculture are proposed. Strains associated in the coculture process are distinguished by their resistance to mitochondrial inhibitors. The xylose-fermenting yeasts are able to grow on media containing erythromycin (1 g/L) or diuron (50 mg/L), whereas the Saccharomyces species are inhibited by these mitochondrial inhibitors.

Candida↗

PubMed1990

Kinetic studies of acetate fermentation by Methanosarcina sp. MSTA-1.

The effect of three parameters (initial acetate concentration, temperature and pH) on the acetoclastic reaction was studied with the thermophilic methanogenic bacterium Methanosarcina sp. MSTA-1. The optimum temperature for growth ranged around 55 degrees C, and optimum pH was 6.5-7.5, giving a minimum generation time of 12.6-13.9 h (mu max = 0.050-0.055 h-1) and a maximum value of the specific acetate consumption rate (qmaxs) of 14-20 mmol/g cells per hour. Contrary to the methane yield, the growth yield was found to be dependent on culture conditions, especially on incubation temperature. Methanosarcina sp. MSTA-1 showed a low affinity for acetate substrate. Growth at 55 degrees C and at constant pH 7 resulted in a Km value and a threshold acetate concentration of 10.7 mM and 0.7 mM, respectively.

Acetates↗

PubMed1988

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.

Journal Article↗

PubMedDate not supplied

[Kinetics of the mycelial growth of Conidiobolus obscurus].

The growth of C. obscurus was studied in solid and liquid media. In agar media, the hyphal growth was linear, but the number of apices increased exponentially; total growth was consequently exponential but characterized by a low growth rate. In batch cultures in a fermenter, mycelial growth was continuously linear following a short exponential phase. The absence of branching induced a linear development of the fungus in liquid culture. Fermentation balances showed that the linear growth could not result from the presence of a specific inhibitor, nor from the existence of a limiting concentration of a nutrient in the medium. Hypotheses concerning the non-branching of the fungus in liquid culture are discussed.

Entomophthora↗