Biomedical subjects

M Clarens

Publications and source records attributed to M Clarens.

8 recordsLinked to original sources

PubMed2002

Monitoring of a pyrite-oxidising bacterial population using DNA single-strand conformation polymorphism and microscopic techniques.

The single-strand conformation polymorphism (SSCP) technique was used to study the evolution of a bacterial consortium during the batch oxidation of a cobaltiferous pyrite in two types of bio-reactor: a bubble column and a classical stirred tank. Sequencing 16S rDNA revealed the presence of three organisms affiliated to Leptospirillum ferrooxidans, Acidithiobacillus thiooxidans and Sulfobacillus thermosulfidooxidans, respectively. Attempts were made to determine the proportions of bacteria attached to solid particles or freely suspended in the medium using a combination of PCR-SSCP and a microscopic technique. Ac. thiooxidans-related bacteria were dominant in the liquid during the early phase of the batch, but were later supplanted by L. ferrooxidans-related bacteria. L. ferrooxidans-related organisms were always in the majority on the solids. The growth of S. thermosulfidooxidans-related bacteria seemed to be favoured by the bubble-column reactor.

Bacteria↗

PubMed2002

An arsenic(III)-oxidizing bacterial population: selection, characterization, and performance in reactors.

AIMS: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. METHODS AND RESULTS: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25 degrees C. As(III) oxidation was still observed in the presence of 1000 mg l(-1) As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l(-1) h(-1). The CASO1 consortium contains at least two organisms - strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5.9%, suggesting that b6 may be a new species. CONCLUSIONS: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. SIGNIFICANCE AND IMPACT OF THE STUDY: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.

Arsenic↗

PubMed1997

Biological treatment of gold ore cyanidation wastewater in fixed bed reactors.

The treatment of a cyanidation effluent containing thiocyanate, free cyanide, and complexed cyanide was continuously performed for a period of 6 months. Activated carbon, pozzolana, and a mixture of pumice stone and zeolite were tested as supports in fixed bed reactors. Activated carbon adsorbed the different forms of cyanide. In contrast, the other supports did not remove any pollutants from the effluent during an adsorption experiment. All supports successfully allowed fixation of bacteria. More than 90% of the thiocyanate was biologically decomposed into NH4+, CO2 and SO4(2-), even when increasing the feed flow-rate and the pollutant concentrations. Free and complexed cyanides were eliminated, probably through a combination of precipitation and biological degradation. The oxidation of ammonium into nitrate was only performed by the activated carbon-containing column and with the more diluted feeding. The nitrification process was inhibited in all reactors when the cyanide concentrations and feed flow-rates were increased.

Journal Article↗

PubMed1995

The archaeal dnaK-dnaJ gene cluster: organization and expression in the methanogen Methanosarcina mazei.

The organization and expression of the first archeael dnaK-dnaJ gene cluster cloned and sequenced have been elucidated. The work focused on the methanogen Methanosarcina mazei strain S-6, but a survey of two other strains (JC3 and LYC) and species (Methanosarcina sp. JCV and Methanosarcina acetivorans) showed that the findings are pertinent to other mesophilic methanosarcinas as well. The organization and some expression features of the archaeal genes resemble eubacterial equivalents for which comparable sequence information is available. However, the archaeal genes also display characteristics that are distinct from those of eubacterial and eucaryotic homologs. dnaK and dnaJ are transcribed into monocistronic messages. The initiation site is the same for transcription under optimal cell-growth conditions, and under stress due to a temperature upshift. The two genes are expressed constitutively at lower levels than those observed after heat shock. The constitutive and post-heat-shock expression levels are higher for dnaK than for dnaJ. Both genes withstand heat shocks of at least one and a half hours without a decline in transcript levels. While the transcription termination signals are to some extent reminiscent of those of eubacteria, the initiation signals are not. These have archaeal characteristics, which resemble those of eukaryotes. The intergenic dnaK-dnaJ region contains inverted repeats. These have the potential to build firm stem-loops in the transcript and in single-stranded DNA.

Base Sequence↗

PubMed1995

Archaeal grpE: transcription in two different morphologic stages of Methanosarcina mazei and comparison with dnaK and dnaJ.

Transcription of the heat shock gene grpE was studied in two different morphologic stages of the archaeon Methanosarcina mazei S-6 that differ in resistance to physical and chemical traumas: single cells and packets. While single cells are directly exposed to environmental changes, such as temperature elevations, cells in packets are surrounded by intercellular and peripheral material that keeps them together in a globular structure which can reach several millimeters in diameter. grpE transcript levels determined by Northern (RNA) blotting peaked after a 15-min heat shock in single cells. In contrast, the highest transcript levels in packets were observed after the longest heat shock tested, 60 min. The same response profiles were demonstrated by primer extension experiments and S1 nuclease analysis. A comparison of the grpE response to heat shock with those of dnaK and dnaJ showed that the grpE transcript level was the most increased, closely followed by that of the dnaK transcript, with that of the dnaJ gene being the least augmented. Transcription of grpE started at the same site under normal and heat shock temperatures, and the transcript was consistently approximately 700 bases long. Codon usage patterns revealed that the three archaeal genes use most codons and have the same codon preference for 61% of the amino acids.

Bacterial Proteins↗

PubMed1993

dnaJ in Archaea.

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Amino Acid Sequence↗

PubMed1992

Methanosarcina mazei JC2, a new methanogenic strain isolated from lake sediments, that does not use H2/CO2.

A new mesophilic methanogenic strain, which produced methane from acetate, methanol, and methylamines, was isolated from lake sediments obtained from the lake Banyoles, near Girona (Spain). The cells were irregular in shape, from 1 to 3 micron in diameter, aggregated in masses of a few to several hundred units. Colonies were about 1-2 mm and irregularly shaped. Their color was yellow or white. Growth occurred throughout the pH range of 5 to 9 with optimal growth around pH 7. The optimal growth temperature was 37 degrees C. The molar deoxiribonucleic acid base composition was 37.2% (G + C). Studies of DNA homologies showed that this isolated was a strain of Methanosarcina mazei, but it differs from other reported strains, in that was not able to use H2/CO2 for growth or methane production.

Acetates↗

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↗