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Biomedical subjects

W Verstraete

Publications and source records attributed to W Verstraete.

At least 163 records · Page 9Linked to original sources
PubMed1990

Phosphonate utilization by bacterial cultures and enrichments from environmental samples.

A selection of axenic microbial strains and a variety of environmental samples were investigated with respect to the utilization of a series of natural and xenobiotic phosphonates as the sole phosphorus source for growth. Phosphonate degradation was observed only with bacteria and not with eucaryotic microorganisms. All representatives of the phosphonates examined supported bacterial growth, with the exception of methylphosphonate diethylester. Yet, distinctly different phosphonate utilization patterns were noted between phosphonate-positive strains. C-P bond cleavage by a photosynthetic bacterium is reported for the first time; growing photoheterotrophically, Rhodobacter capsulatus ATCC 23782 was able to utilize 2-aminoethylphosphonate and alkylphosphonates. Bacteria with the potential to utilize at least one of the phosphonate moieties from the xenobiotic phosphonates Dequest 2010, Dequest 2041, and Dequest 2060 were detected in all environments, with only two exceptions for Dequest 2010. Phosphonate P utilization to an extent of 94 and 97%, for Dequest 2010 and Dequest 2041, respectively, provided evidence that a complete breakdown of these compounds with respect to the C-P bond cleavage can be achieved by some bacteria. The results suggest that phosphonate-utilizing bacteria are ubiquitous, and that selected strains can degrade phosphonates that are more complex than those described previously.

Bacteria↗
PubMed1990

Gene escape model: transfer of heavy metal resistance genes from Escherichia coli to Alcaligenes eutrophus on agar plates and in soil samples.

Conjugal transfer from Escherichia coli to Alcaligenes eutrophus of the A. eutrophus genes coding for plasmid-borne resistance to cadmium, cobalt, and zinc (czc genes) was investigated on agar plates and in soil samples. This czc fragment is not expressed in the donor strain, E. coli, but it is expressed in the recipient strain, A. eutrophus. Hence, expression of heavy metal resistance by cells plated on a medium containing heavy metals represents escape of the czc genes. The two plasmids into which this DNA fragment has been cloned previously and which were used in these experiments are the nonconjugative, mobilizable plasmid pDN705 and the nonconjugative, nonmobilizable plasmid pMOL149. In plate matings at 28 to 30 degrees C, the direct mobilization of pDN705 occurred at a frequency of 2.4 x 10(-2) per recipient, and the mobilization of the same plasmid by means of the IncP1 conjugative plasmids RP4 or pULB113 (present either in a third cell [triparental cross] or in the recipient strain itself [retromobilization]) occurred at average frequencies of 8 x 10(-4) and 2 x 10(-5) per recipient, respectively. The czc genes cloned into the Tra- Mob- plasmid pMOL149 were transferred at a frequency of 10(-7) to 10(-8) and only by means of plasmid pULB113. The direct mobilization of pDN705 was further investigated in sandy, sandy-loam, and clay soils. In sterile soils, transfer frequencies at 20 degrees C were highest in the sandy-loam soil (10(-5) per recipient) and were enhanced in all soils by the addition of easily metabolizable nutrients.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcaligenes↗
PubMed1987

Microbial parameters and their control in anaerobic digestion.

Parameters, such as pH, loading-rate, space, substrate limitation and cell (dis) aggregation, are critical in anaerobic digestion. A better understanding of these parameters is necessary to achieve a more successful operation of anaerobic digesters.

Aerobiosis↗
PubMed1986

Sulfate reduction relative to methane production in high-rate anaerobic digestion: technical aspects.

The effect of different substrates and different levels of sulfate and sulfide on methane production relative to sulfate reduction in high-rate anaerobic digestion was evaluated. Reactors could be acclimated so that sulfate up to a concentration of 5 g of sulfate S per liter did not significantly affect methanogenesis. Higher levels gave inhibition because of salt toxicity. Sulfate reduction was optimal at a relatively low level of sulfate, i.e., 0.5 g of sulfate S per liter, but was also not significantly affected by higher levels. Both acetoclastic and hydrogenotrophic methane-producing bacteria adapted to much higher levels of free H(2)S than the values reported in the literature (50% inhibition occurred only at free H(2)S levels of more than 1,000 mg/liter). High levels of free H(2)S affected the sulfate-reducing bacteria only slightly. Formate and acetate supported the sulfate-reducing bacteria very poorly. In the high-rate reactors studied, intensive H(2)S formation occurred only when H(2) gas or an H(2) precursor such as ethanol was supplied.

Journal Article↗
PubMed1986

Sulfate reduction relative to methane production in high-rate anaerobic digestion: microbiological aspects.

In the high-rate anaerobic reactors studied (ca. 10 g of chemical oxygen demand [COD] removed per liter of reactor per day), the sulfate-reducing bacteria (SRB) were poor competitors of methane-producing bacteria (MPB), scavenging only on the order of 10 to 20% of the total electron flow. The relatively noncompetitive nature of the SRB in this type of reactor is in sharp contrast to the tendency of the SRB to dominate in natural environments and in other types of anaerobic digesters. Various factors such as the feedback inhibition of H(2)S on the SRB, iron limitation, the origin of the SRB inocula, biokinetics, and thermodynamics were investigated. The outcome of the SRB-MPB competition under the reactor conditions studied appeared to be particularly determined by two factors. The SRB, as predicted by the V(max)-K(m) kinetics, competed most effectively at low substrate levels (<0.5 g of COD per liter). The MPB, however, appeared to colonize and adhere much more effectively to the polyurethane carrier matrix present in the reactor, thus compensating for the apparent lower growth rates. Even if the reactor was initially allowed to be predominantly colonized by SRB, the MPB could regain dominance.

Journal Article↗
PubMed1984

[Spontaneous hernia of the brain into the temporal bone].

A case of spontaneous brain hernia into the middle ear cleft is described. Even without preceding infection, trauma or surgery of the mastoid, dural and cerebral tissue may protrude into the antrum or middle ear space. The pathology of this rare disease is discussed.

Aged↗
PubMed1979

Biodegradability of Tioctilate.

The biodegradability of Tioctilate (octylthiobenzoate), a new pesticide, has been examined by means of 5 tests. The compound appears to be susceptible to microbial metabolism.

Aerobiosis↗
PubMed1978

Evaluation of yield and maintenance coefficients, expressed in carbon units, for Pseudomonas fluorescens and P. aeruginosa.

The maximum cell yield (YMc - g biomass carbon per gram substrate carbon) and the rate of maintenance metabolism (mc - g substrate carbon/g biomass carbon per hour) have been determined for substrate limited continuous cultures of Pseudomonas fluorescens and P. aeruginosa. The metabolism of the organic substrates was monitored by measuring the COD-removal1) rates at different dilution rates. The advantages of expressing yield and maintenance coefficients in carbon units is discussed.

Bacteriological Techniques↗
PubMed1977

Double-blind placebo-controlled clinical evaluation of oxatimide (R 35443). A novel potent anti-allergic drug in the treatment of hay fever.

The efficacy of the new anti-allergic compound oxatimide was tested in a double-blind study against a placebo during the pollen season of 1976 in 215 patients (4 1/2--69 years) with hay fever. Adult patients were instructed to take two tablets (= 20 mg) three times a day for 2 weeks, children received one tablet/10 kg of body weight daily; in addition, they were given a supply of diphenhydramine as a potential supplement. Twelve patients, six from either group, were excluded from the analysis. A significantly higher proportion of patients from the active drug group (n = 104) experienced no or only a few days of complaints, i.e. rhinitis and conjunctivitis, as well as asthma-like complaints, as compared with those of the control group (n = 99). Also, diphenhydramine consumption became significantly lower in the active drug group from the second day onwards, whereas a gradual increase and continuous need were seen in the greater part of the control group. One week of treatment appears sufficient to judge whether the individual patient benefits from the drug or not.

Administration, Oral↗
PubMed1975

Competitive ability of amylolytic bacteria in activated sludge.

Shifts were induced into the microbial community of activated sludge by the pulse addition of soluble starch. The subsequent changes of amylolytic and proteolytic microbial populations were recorded. Four amylolytic strains were isolated and characterized with regard to carrying capacity, specific surface and growth kinetics. The competitive ability of these strains was studied by means of two-member competition experiments. These experiments were analysed according to the Lotka-Volterra model and the de Wit method. The different results obtained suggest that the dominance of the amylolytic Pseudomonas sp. (code 01) is based on a combined occurrence of high amylolytic activity, large relative cell surface, high maximum specific growth rate and reduced sensitivity towards associated proteolytic populations.

Aeromonas↗
PubMed1972

Heterotrophic nitrifiction by Arthrobacter sp.

Arthrobacter sp. isolated from sewage oxidized ammonium to hydroxylamine, a bound hydroxylamine compound, a hydroxamic acid, a substance presumed to be a primary nitro compound, nitrite, and nitrate. The concentration of free hydroxylamine-nitrogen reached 15 mug/ml. The identification of hydroxylamine was verified by mass spectrometric analysis of its benzophenone oxime derivative. The bound hydroxylamine was tentatively identified as 1-nitrosoethanol on the basis of its mass spectrum, chemical reactions, and infrared and ultraviolet spectra. Hydroxylamine formation by growing cells was relatively independent of pH, but the accumulation of nitrite was strongly favored in alkaline solutions. The formation of hydroxylamine but not nitrite was regulated by the carbon to nitrogen ratio of the medium. The hydroxamic acid was the dominant product of nitrification in iron-deficient media, but hydroxylamine, nitrite, and 1-nitrosoethanol formation was favored in iron-rich solutions. Heterotrophic nitrification by Arthrobacter sp. was not inhibited by several compounds at concentrations which totally inhibited autotrophic nitrification.

Acetates↗
PubMed1972

Mechanism of nitrification by Arthrobacter sp.

Resting cells of Arthrobacter sp. excrete as much as 60 mug of hydroxylamine-nitrogen per ml when supplied with ammonium. An organic carbon source in abundant supply is necessary for the oxidation. Resting cells oxidize hydroxylamine to nitrite and 1-nitrosoethanol, the former accumulating only when an exogenous carbon source is available. Cell-free extracts contain an enzyme catalyzing the formation of hydroxylamine from acetohydroxamic acid, a hydroxylamine-nitrite oxido-reductase, and an enzyme producing nitrite and nitrate from various primary nitro compounds. Nitrite is not produced from hydroxylamine by the extracts, but 1-nitrosoethanol is formed from hydroxylamine in the presence of acetate. 1-Nitrosoethanol is also produced from acetohydroxamic acid by these preparations. Nitrite was formed from hydroxylamine, however, by extracellular enzymes excreted by the bacterium.

Acetates↗
PubMedDate not supplied

Polycyclic aromatic hydrocarbons (PAHs) and estrogenic compounds in experimental flue gas streams.

The importance of combustion processes as a source of substances with estrogenic activity in the environment was investigated. Wood (nontreated and treated with wood preservatives), barbecue charcoal, meat, and kitchen waste were combusted in a laboratory-scale incinerator. Flue gas emissions (particulates and gaseous pollutants) were trapped in polyurethane foam cartridges. The cartridges were subjected to Soxhlet extraction and part of the extracts redissolved in dimethylsulfoxide (DMSO) for analyses of estrogenic activity by means of the yeast-based human estrogen receptor (hER) bioassay. A synthetic estrogen, 17-alpha-ethinylestradiol (EE2), was used as the reference estrogenic compound. Part of the extracts was analyzed for the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). Estrogenic compounds in the flue gas (wood) were as high as 234 +/- 25 ng m(-3) EE2 equivalent compared with 27 to 81 ng m(-3) EE2 equivalent in flue gas from combustion of barbecue charcoal. Concentrations of polycyclic aromatic hydrocarbons in both flue gas streams were in the range of 21,000 +/- 2000 and 240 +/- 110 ng m(-3), respectively. In general, the concentrations of EE2 equivalent in the flue gas samples were at least a factor of 1000 lower than total PAH concentration. The EE2 levels were not related to the concentration of PAHs in any flue gas sample.

Air Pollutants↗