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Biomedical subjects

J A De Bont

Publications and source records attributed to J A De Bont.

9 recordsLinked to original sources
PubMed2000

Continuous production of enantiopure 1,2-epoxyhexane by yeast epoxide hydrolase in a two-phase membrane bioreactor.

A two-phase membrane bioreactor was developed to continuously produce enantiopure epoxides using the epoxide hydrolase activity of Rhodotorula glutinis. An aqueous/organic cascade, hydrophilic, hollow-fiber membrane bioreactor was used: (1) to carry out large-scale resolution of epoxides, (2) to continuously extract residual enantiopure epoxides from the aqueous phase, and (3) to separate inhibitory formed diol from the yeast cells contained in the aqueous phase. Dodecane was employed to dissolve-feed epoxide as well as to extract residual epoxide. 1,2-Epoxyhexane was used as a model substrate. By use of this membrane bioreactor, enantiopure (S)-1,2-epoxyhexane (>98% enantiomeric excess) was obtained with a volumetric productivity of 3.8 g l(-1) h(-1). The continuous-production system was operated for 12 days and resulted in 38 g enantiopure (S)-1,2-epoxyhexane.

Alkanes↗
PubMed2000

The solvent efflux system of Pseudomonas putida S12 is not involved in antibiotic resistance.

The active efflux system contributing to the solvent tolerance of Pseudomonas putida S12 was characterized physiologically. The mutant P. putida JK1, which lacks the active efflux system, was compared with the wild-type organism. None of 20 known substrates of common multi-drug-resistant pumps had a stronger growth-inhibiting effect on the mutant than on the wild type. The amount of [14C]toluene accumulating in P. putida S12 increased in the presence of the solvent xylene and in the presence of uncouplers. The effect of uncouplers confirms the proton dependency of the efflux system in P. putida S12. Other compounds, potential substrates for the solvent pump, did not affect the accumulation of [14C]toluene. These results show that the efflux system in P. putida S12 is specific for organic solvents and does not export antibiotics or other known substrates of multi-drug-resistant pumps.

Anti-Bacterial Agents↗
PubMed1999

Resolution of 1,2-epoxyhexane by Rhodotorula glutinis using a two-phase membrane bioreactor.

Large-scale resolution of epoxides by the yeast Rhodotorula glutinis was demonstrated in an aqueous/organic two-phase cascade membrane bioreactor. Due to the chemical instability and low solubility of epoxides in aqueous phases, an organic solvent was introduced into the reaction mixture in order to enhance the resolution of epoxide. A cascade hollow-fiber membrane bioreactor was used (1) to minimize the toxicity of organic solvents towards the epoxide hydrolase of R. glutinis, and (2) to remove inhibitory amounts of formed diol from the yeast cell containing aqueous phase. Dodecane was selected as a suitable solvent and 1,2-epoxyhexane as a model substrate. By use of this membrane bioreactor, highly concentrated (0.9 M in dodecane) enantiopure (> 98% ee) (S)-1,2-epoxyhexane (6.5 g, 30% yield) was obtained from the racemic mixture.

Bioreactors↗
PubMed1992

Aerobic vinyl chloride metabolism in Mycobacterium aurum L1.

Mycobacterium aurum L1, capable of growth on vinyl chloride as a sole carbon and energy source, was previously isolated from soil contaminated with vinyl chloride (S. Hartmans et al., Biotechnol. Lett. 7:383-388, 1985). The initial step in vinyl chloride metabolism in strain L1 is catalyzed by alkene monooxygenase, transforming vinyl chloride into the reactive epoxide chlorooxirane. The enzyme responsible for chlorooxirane degradation appeared to be very unstable and thus hampered the characterization of the second step in vinyl chloride metabolism. Dichloroethenes are also oxidized by vinyl chloride-grown cells of strain L1, but they are not utilized as growth substrates. Three additional bacterial strains which utilize vinyl chloride as a sole carbon and energy source were isolated from environments with no known vinyl chloride contamination. The three new isolates were similar to strain L1 and were also identified as Mycobacterium aurum.

Biodegradation, Environmental↗
PubMed1976

Nitrogen fixation by hydrogen-utilizing bacteria.

Seventeen strains of nitrogen-fixing bacteria, isolated from different habitats on hydrogen and carbon dioxide as well as on other substrates, morphologically resembled each other. All strains, including Mycobacterium flavum 301, grew autotrophically with hydrogen. The isolate strain 6 was sensitive to oxygen when dependent on N2 as nitrogen source, a consequence of the sensitivity of its nitrogenase towards oxygen. At the same time, strain 6 was sensitive to hydrogen when growing autotrophically on N2 as nitrogen source, but hydrogen did not affect acetylene reduction by these cells.

Acetylene↗
PubMed1976

Oxidation of ethylene by soil bacteria.

The course of the biological oxidation of ethylene by soil was dependent on the type of soil used as well as on other factors. As evidenced from an increase in oxidation rate, the ethylene-consuming microorganisms in soil could grow at the expense of ethylene, even when the gas was present at concentrations of 50 ppm or less. Five strains of bacteria strongly resembling each other were isolated from different soils. These pleomorphic, gram-positive, acid-fast, obligate aerobic, ethylene-oxidizing bacteria grew also on saturated alkanes and on ordinary carbon sources. An apparent Km for ethylene of approximately 40 ppm was estimated for whole-cell suspensions of strain E20 by following the disappearance of the gas from the atmosphere.

Bacteria↗
PubMed1976

Microbial metabolism of ethylene.

The ethylene-oxidizing strain E20 was grown on different carbon sources to obtain information on the metabolism of ethylene from simultaneous adaptation studies and from measurements of specific activities of enzymes in cell-free extracts. From the simultaneous adaptation studies it was concluded that ethylene oxide is a product of ethylene catabolism. The bacterium was also able to grow on the epoxide. From a comparison of the specific activities of isocitrate lyase and malate synthetase in different extracts it was concluded that the glyoxylate cycle was involved in the metabolism of ethylene, indicating that acetyl-CoA is a metabolite of ethylene catabolism. The sequence of reactions leading from ethylene oxide to acetyl-CoA could not be established from the simultaneous adaptation experiments and the enzyme activities in extracts.

Acetate-CoA Ligase↗
PubMed1976

Invalidity of the acetylene reduction assay in alkane-utilizing, nitrogen-fixing bacteria.

The cause of the failure of the C2H2-C2H4 assay for nitrogen-fixing bacteria growing on lower alkanes was studied. Acetylene was a strong competitive inhibitor of methane oxidation for methane-utilizing bacteria, as well as for the oxidation of lower alkanes by other bacteria, so that energy and reducing power were no longer available for the reduction of acetylene by nitrogenase. Nitrogen-fixing bacteria grown on alkanes may reduce acetylene when intermediates of alkane-breakdown or other substrates oxidizable in the presence of acetylene are supplied. Ethylene co-oxidation is not responsible for the failure of the test, because acetylene also inhibits this co-oxidation along with methane oxidation.

Acetylene↗