Biomedical subjects
Publications and source records attributed to L A Nagy.
Six media (Czapek, Martin's, Mycological, Nutrient, Sabouraud Dextrose and Sabouraud Maltose), were evaluated for their ability to recover filamentous fungi from aqueduct biofilm. Average filamentous fungal levels detected by the six media ranged from 46-250 CFU/cm2 of biofilm. Of the media tested, Nutrient, Czapek and Sabouraud Dextrose provided the highest relative recoveries.
The Elliot Lake-Blind River, Ontario, paleoplacer deposits in the basal Matineda Formation, lowermost member of the 2.25-2.45 Ga old Huronian Supergroup, contain organic matter chemically consistent with kerogen. This substance is also referred to as thucholite. Uranium ores and some gold occur here, and these minerals may be in close association with the kerogen. Two uraniferous and auriferous stratiform kerogens, obtained from the Denison Mines Limited's Denison mine and Rio Algom Limited's Stanleigh mine, have been analyzed by combined high-vacuum pyrolysis--gas chromatography--mass spectrometry and by neutron activation. The reflectances of these samples have also been determined. Related samples containing dispersed kerogen have been examined by backscattered scanning electron microscopy. The polymer-like matrix of the two stratiform kerogens consists of aromatic, alkyl aromatic hydrocarbon, and sulphur moieties and contains 20 and 32% uranium with gold abundances in the parts per billion range. The reflectances of the two kerogens are generally higher than those of the dispersed kerogens; the atomic H/C ratios of the former are approximately 0.6 and approximately 0.4. Backscattered scanning electron microscopy and petrographic observations reveal a complex diagenetic history. Stratigraphic position and supportive analytical data suggest that the stratiform kerogens were probably derived from ancient mats of cyanobacteria, subjected to various radiation-induced reactions, and, at least in part, were affected in a manner similar to the surrounding rocks. The latter experienced physical and chemical diagenetic reactions, which often caused repeated mineral fracturing and led to the local development of authigenic carbonates and feldspar. Some of the chemical nature and history of the stratiform kerogens resemble those of the Witwatersrand carbon seam kerogen.
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The densities of filamentous fungal colonies, together with physicochemical and bacteriological parameters, were assessed in a chlorinated and unchlorinated drinking water distribution system at eight separate times over a period of 1 year. Filamentous fungal colonies were enumerated by membrane filtration on Czapek-Dox agar. The mean number of filamentous fungal colony-forming units per 100 mL of drinking water was 18 in the unchlorinated and 34 in the chlorinated system. The majority of filamentous fungi isolated wee saprophytic Deuteromycotina. The four most frequently occurring genera were Penicillium, Sporocybe, Acremonium, and Paecilomyces. In the chlorinated system, only physicochemical parameters correlated with observed fungal frequencies, whereas in the unchlorinated system, none of the parameters exhibited significant correlations with fungal numbers.
Microfossils, probably representing members of Precambrian photosynthetic communities of bacteria and blue-green algae, have been found in the approximately 2800-2500 million-year-old Bulawayan stromatolites from Rhodesia. Several populations of coccoid and elongate microfossils have been observed in the dark, carbon-rich stromatolite laminae. Some of these elongate forms are morphologically similar to modern bacterial spores. These microfossils were studied in petrographic thin sections and identified by combined scanning electron microscopy-electron microprobe and by analyses of energy dispersive spectra of individual microfossils. The microfossils contain 1-20% organic carbon; some morphotypes contain traces of sulfur and one other, traces of phosphorus. The polymeric nature of the organic carbon was established by analyzing aggregates of microfossils at elevated temperatures in the solid inlet system of an organic mass spectrometer. The coccoid microfossils range in size from 1.2 to 4.3 mum, the elongate microfossils are from 2.4 to 9.8 mum. They are mineralized with dolomite, embedded in a calcite matrix, and are shown to be both indigenous and syngenous with the rock. Identical microfossils also containing organic carbon but mineralized with quartz have been observed in the stromatolites from Belingwe which are part of the Bulawayan Group from Rhodesia. Caution must be used in the interpretation of what these forms are because of their great age and relatively simple morphologies. However, based on morphology and chemical analyses, they represent fossilized bacteria, blue-green algae, or, most likely, both.
An Early Precambrian micaceous metaquartzite subjected to low to moderate metamorphism in the Isua area of Southwestern Greenland was derived from the erosion of preexisting rocks which were probably sialic in composition. This metaquartzite may have been formed before the emergence of life. It contains globular particles of graphite arranged in narrow veins or along foliation or bedding planes. This rock contains no organic compounds besides traces of methane and no biologically significant elements associated with the graphite microstructures. Reaction of primitive methane with ferric oxides appears to have oxidized the methane to the vein graphite and reduced the ferric oxides to ferrous-ferric oxide (magnetite). The graphitic microstructures are likely to be abiotic in origin, although a biological origin is not impossible. Somewhat younger microstructures found in other locations on earth have often been described as microfossils; this origin should be reexamined on the basis of the above mentioned conclusions.
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Are they entrapped solar wind particles, meteoritic or cometary contributions, remnants of a primordial atmosphere or products of the degassing of the Moon ?