Biomedical subjects

K B Zwart

Publications and source records attributed to K B Zwart.

4 recordsLinked to original sources

PubMed1997

Stable-Isotope Analysis of a Combined Nitrification-Denitrification Sustained by Thermophilic Methanotrophs under Low-Oxygen Conditions.

To simulate growth conditions experienced by microbiota at O(inf2)-limited interfaces of organic matter in compost, an experimental system capable of maintaining dual limitations of oxygen and carbon for extended periods, i.e., a pO(inf2)-auxostat, has been used. (sup15)N tracer studies on thermophilic (53(deg)C) decomposition processes occurring in manure-straw aggregates showed the emission of dinitrogen gas from the reactor as a result of simultaneous nitrification and denitrification at low pO(inf2) values (0.1 to 2.0%, vol/vol). The N loss was confirmed by nitrogen budget studies of the system. Depending on the imposed pO(inf2), 0.6 to 1.4 mmol of N/day (i.e., 20 to 40% of input N) was emitted as N(inf2). When the pO(inf2) was raised, the rates of both nitrification and denitrification increased instantaneously, indicating that ammonia oxidation was limited by oxygen. In auxostats permanently running at pO(inf2) >= 2% (vol/vol), the free ammonium pool was almost completely oxidized and was converted to nitrite plus nitrate and N(inf2) gas. Labelling of the auxostat with [(sup13)C]carbonate was conducted to reveal whether nitrification was of autotrophic or heterotrophic origin. Incorporation of (sup13)CO(inf2) into population-specific cellular compounds was evaluated by profiling the saponifiable phospholipid fatty acids (FAs) by using capillary gas chromatography and subsequently analyzing the (sup13)C/(sup12)C ratios of the individual FAs, after their combustion to CO(inf2), by isotope ratio mass spectrometry. Apart from the observed label incorporation into FAs originating from a microflora belonging to the genus Methylococcus (type X group), supporting nitrification of a methylotrophic nature, this analysis also corroborated the absence of truly autotrophic nitrifying populations. Nevertheless, the extent to which ammonia oxidation continued to exist in this thermophilic community suggested that a major energy gain could be associated with it.

Journal Article↗

PubMed1986

Symbiosis of protozoa with hydrogen-utilizing methanogens.

The symbiotic interaction between bacteria and protozoa is a well-known phenomenon. Endosymbiosis of bacteria in the amoeba Pelomyxa was reported as early as 1902 by Pénard and since then endosymbiosis has been described for a variety of protozoa by many authors. Also episymbiosis of bacteria and protozoa has been observed frequently. However, surprisingly little is known about the physiological interaction of both partners in such a close association. This is mostly because of problems that arise in characterizing the bacteria, and the unknown nature of excretion products of one partner utilized by the other. The discovery of some unique fluorescent cofactors involved in methane biochemistry which are specific for methanogenic bacteria enabled recognition of these microorganisms by fluorescence microscopy. Using this technique, several symbiotic associations between anaerobic protozoa and methanogenic bacteria have been found. The aim of this paper is to review the field and to discuss the possible functions of symbiosis for both bacteria and protozoa.

Animals↗

PubMed1984

Methanogenesis: surprising molecules, microorganisms and ecosystems.

Methanogenesis involves a novel set of coenzymes as one-carbon and electron carriers. Consequently, metabolic processes of methanogens deviate from those present in non-methanogenic bacteria. Methanogenic bacteria can be classified on the basis of substrate utilization. Group I (24 species) grows at the expense of hydrogen plus CO2 and/or formate and group II (7 species) uses methanol and/or acetate. Hydrogen-consuming methanogens are found as epi- or endosymbionts of anaerobic ciliates.

Acetates↗

PubMed1983

Significance of yeast peroxisomes in the metabolism of choline and ethanolamine.

The yeasts Candida utilis and Hansenula polymorpha were able to grow in media containing choline or ethanolamine as the sole nitrogen source. During growth in the presence of these substrates, large peroxisomes developed in the cells, and extracts of choline-grown C. utilis cells contained increased levels of amine oxidase and catalase. Incubation of whole cells with choline in the presence of the amine oxidase inhibitor aminoacetonitrile led to excretion of dimethylamine and methylamine. Cytochemical experiments in which spheroplasts prepared from choline-grown cells were incubated with CeCl3 and choline, trimethylamine, dimethylamine or methylamine revealed positively stained peroxisomes, whereas in the presence of 1 mM aminoacetonitrile staining was not observed. This indicated that choline was degraded via methylated amines and that peroxisomes played a role in its metabolism. A similar involvement of peroxisomes in choline degradation was observed in H. polymorpha. Cell-free extracts of ethanolamine-grown C. utilis and H. polymorpha also contained increased levels of amine oxidase and catalase. Ethanolamine was oxidized by cell-free extracts of both organisms after growth in the presence of ethanolamine or choline. Incubation of spheroplasts of ethanolamine- or choline-grown C. utilis with CeCl3 and ethanolamine resulted in positively stained peroxisomes. In this organism peroxisomes were therefore also involved in ethanolamine degradation.

Ascomycota↗