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51.
52.
Nitrification and denitrification by Thiosphaera pantotropha in aerobic chemostat cultures 总被引:4,自引:0,他引:4
Abstract: Thiosphaera pantotropha has been reported to denitrify aerobically and nitrify heterotrophically. However, recent evidence has indicated that these properties (particularly aerobic denitrification) have been lost. The occurrence and levels of aerobic denitrification and heterotrophic nitrification by T. pantotropha in chemostat cultures have therefore been re-evaluated. Only low nitrate reduction rates were observed: the apparent nitrogen loss was of the same order of magnitude as the combined error in the calculated nitrogen consumption. However, 15 N mass spectrometry revealed low aerobic denitrification rates (about 10% of the rates originally published by this group). Heterotrophic nitrification rates were about a third of previous observations. N2 and N2 O were both produced from NH4 + , NO3 − and NO2 − . Periplasmic nitrate reductase was present in aerobically grown cells. 相似文献
53.
Summary Qualitative and quantitative aspects of heterotrophic carbon assimilation by mycorrhizal plants of birch (Betula pendula) were examined. Plants were grown aseptically from seed in the mycorrhizal condition with the fungus Hebeloma crustuliniforme and in the non-mycorrhizal condition, with protein as their sole exogenous nitrogen source. Yields and nitrogen contents were determined in some of the plants, while the roots of others were supplied with 14C-labelled protein and their shoots exposed for up to 72 h to different irradiance regimes. Only mycorrhizal plants utilised the organic nitrogen. Uptake of carbon associated with this utilisation and its translocation to the leaves was demonstrated directly by means of autoradiography. Amounts of activity transferred to shoots were greatest in low irradiance regimes. Calculation of net carbon gain from the heterotrophic source, based upon the assumption that breakdown products of protein are assimilated as amino-acids, indicates that over a 55-day growth period up to 9% of plant C may be derived from protein. The physiological and ecological significance of these findings are discussed. 相似文献
54.
Christine M. Happey-Wood 《Journal of phycology》1980,16(1):116-128
The occurrence, periodicity and growth of twenty species of unicellular Volvocales on sediments in an acidic pool are described. Minimum populations were recorded in winter, but during the rest of the year standing crops fluctuated rapidly. The greatest species diversity and primary productivity occurred in late spring-early summer and in autumn, when maximum numbers of Chlamydomonas spp. and Chloromonas spp. increased exponentially on the sediments. The chlamydomonads were more numerous in the epipelon than other major algal components such as diatoms, euglenoids, bluegreen algae and desmids. Growth of the chlamydomonad population occurred after the period of maximum diatom standing crop. Evidence shows that rates of primary production were greater in late spring and late summer when species diversity and standing crop or apparent growth rates of unicellular Volvocales were high. Thus these algae which are normally neglected may be more important in primary productivity than previously believed since they grow during periods when larger algae are scarce. Analysis of the data using the multivariate technique of Reciprocal Averaging confirmed seasonal periodicity in this community of epipelic flagellates. It also identified species with distinctive ecological requirements. A relationship between the bicarbonate-alkalinity of the overlying water and the chlamydomonad population was demonstrated by ordination analysis. 相似文献
55.
Summary Recent evidence has shown that algal cells acquire different flagella and a heterogeneous basal apparatus through the prolonged development of these structures over more than one cell cycle. A system for numbering algal flagella and basal bodies, which is based on developmental studies, is discussed along with the various means by which the flagellar/basal body developmental cycle can be determined. We review the information now available on development of the separate components of the flagellar apparatus-this comes particulary from the Chlorophyta and the Chromophyta-and attempt to elucidate any information which may help in phylogenetic comparisons. New data is provided on developmental changes in the cartwheel part of the basal body and basal body-associated connecting fibrils in green algae.Abbreviations Bb
basal body
- d
right (dexter) root
- df
right fibrils connecting Bb triplets to microtubular and/or fibrous roots
- EM
electron microscopy
- F
flagellum
- IMF
immunofluorescence microscopy
- LM
light microscopy
- NBBC
nucleus-basal body connector
- s
left (sinister) root
- sf
3left fibrils connecting Bb triplets to microtubular and/or fibrous roots. See Nomenclature section of Introduction for the numbering of basal bodies and their flagella; the same numbers apply to Bb-associated d and s roots, and df and sf fibrils 相似文献
56.
57.
Annette Petersen 《Hydrobiologia》1990,191(1):255
Summary The seasonal variation in densities of heterotrophic flagellates and ciliates was examined for one year in the shallow hypertrophic Lake Søbygård, Denmark.Several peaks in numbers of bacteria, heterotrophic flagellates and ciliates were seen in spring and late autumn. The peak of heterotrophic flagellates occurred 3–9 days after the peak in bacteria. Ciliates peaked 3–6 days later than the heterotrophic flagellates. This pattern was not found in summer and autumn, probably due to predation and grazing influences by the macro-zooplankton.For enumeration of the heterotrophic flagellates a modification of the proflavine staining technique of Haas (1982) was used.Ciliates were counted on the < 20 µ and < 10 µm Lugol-fixed samples after live filtration on monofile nylon nets. During the investigation, however, it was shown that some ciliates were damaged by filtration.To investigate whether the filtration had any significant effect on total numbers, a series of filtration experiments was performed (Fig. 1).In this experiment, the live filtration showed a 30-fold underestimation. Several tests during the season confirmed this error tendency.In my opinion it is, therefore, only possible to enumerate ciliates in unfiltered samples. 相似文献
58.
59.
KEITH VICKERMAN 《The Journal of eukaryotic microbiology》1973,20(3):394-404
SYNOPSIS. The ultrastructure of attached Trypanosoma vivax epimastigote clusters in the proboscis of the tsetse fly Glossina fuscipes is described from electron micrographs of thin sections. Some flagellates are attached directly to the lining of the insect's labrum by their flagella, most of which are aligned along the long axis of the proboscis. Other trypanosomes are attached indirectly, their flagella adhering to those of flagellates which are directly attached. Junctional complexes similar to those described from metazoan epithelia are found on the flagellar membrane. A long zonular hemidesmosome attaches the flagellum to the proboscis wall and a series of closely set macular desmosomes link the flagellar membranes of adjacent flagellates. Unlike the trypomastigote stages of T. vivax, more than one row of macular desmosomes may be present along the flagellum-body junction of the trypanosome. It is suggested that all these Junctional complexes serve to buttress the flagellate's attachment to its insect host and so maintain anchorage of the parasite during the fly's blood meals. The ability of the flagellum of trypanosomatids to form Junctional complexes may be a factor contributing to their success as parasites, this adaptation enabling them to multiply while attached to host surfaces. 相似文献
60.
Grim JN 《The Journal of eukaryotic microbiology》2006,53(4):269-274
During the past 16 years, the ciliate Balantidium jocularum has been collected from the intestines of many specimens of its fish host, Naso tonganus, all collected from the Great Barrier Reef near Lizard Island, Australia. Ciliates for this study of food consumption were isolated in 1988, 1989, 2003, and 2005. Nineteen specimens of B. jocularum were examined in the transmission electron microscope to determine the contents of both food vacuoles and a putative discharging cytoproct vacuole. Food vacuoles contained rod-shaped bacteria, tightly coiled spirilliform bacteria, and one or more euglenid flagellates. In several balantidia of somewhat different form than the type species of B. jocularum, the large bacterium, Epulopiscium fishelsoni, was observed in light microscope protargol preparations. Some putative phagolysosomes retained spirilliform bacteria that were apparently intact, and others contained partially digested flagellates. Food in a single discharging cytoproct vacuole consisted of normal appearing spirilliform bacteria, some other bacteria, and no flagellates. The results argue for non-selective ingestion of food and selective digestion; hence, somewhat inefficient food processing. 相似文献