Joanna V. Abraham-Peskir

Conditions for biological precipitation of iron by Gallionella ferruginea in a slightly polluted ground water

Abstract A sand filter has been built as a pilot plant with the purpose of biological precipitation of Fe from ground water polluted with mainly chlorinated aliphatics. The ground water is pumped directly from a well in a polluted ground water aquifer in Esbjerg, Denmark. The pollution includes trichlorethylene and tetrachlorethylene together with smaller amounts of pesticides. Furthermore the best conditions for Fe precipitating bacteria were not expected to be present because of a relatively high O 2 content, up to 6.7 mg/l, a low Fe content, 0.2 mg/l and a pH of ∼5 in the ground water. Added FeSO 4 increased the Fe content of the ground water to about 4 mg/l. These rather extreme conditions for precipitating Fe were observed over a period of 3 months. The goal of the research was to observe the mechanism of Fe precipitation in a sand filter in the above-mentioned conditions comparative to normal conditions for biotic as well as abiotic Fe mineralization in sand filters of fresh water treatment plants. The Fe precipitating bacterium Gallionella ferrugenia was found to dominate the biotic Fe oxidation/precipitation process despite the extreme conditions. A huge amount of exopolymer from Gallionella was present. The precipitated Fe oxide was determined to be ferrihydrate. The rate of the Fe oxidation/precipitation was found to be about 1000 times faster than formerly found for abiotic physico-chemical oxidation/precipitation processes. The hydrophobic pesticides and some of their degradation products were not adsorbed in the filter. An added hydrophilic pesticide was adsorbed up to 40%. Trichlorethylene was not adsorbed in the filter. The reason for the poor adsorption of the hydrophobic compounds and trichlorethylene is due to the pronounced hydrophilic property of the exopolymers of Gallionella and the precipitated ferrihydrite.

Conditions and Rates of Biotic and Abiotic Iron Precipitation in Selected Danish Freshwater Plants and Microscopic Analysis of Precipitate Morphology

Abstract This study compares the biotic precipitation of iron in the sand filters of a new freshwater plant, Astrup, with the abiotic precipitation of iron in the sand filters of a traditional freshwater plant, Forum, in the same area of Denmark. We have observed that a third freshwater plant, Grindsted, which was planned to precipitate iron in the traditional abiotic way is in fact precipitating iron biotically because of poor aeration and very low oxygen content of the raw water. The dominant iron-precipitating bacteria was Gallionella ferruginea in both Astrup and Grindsted. The morphology of the iron precipitates were investigated using light, X-ray, scanning electron and transmission electron microscopy. The physicochemical conditions governing precipitation and the precipitated iron sludge were also investigated. The biotically precipitated iron was shown to be oxidised and precipitated with a rate about 60 times faster than the traditional abiotic process in spite of the much poorer physicochemical conditions for the process. The faster kinetics indicate a catalytic activity due to the presence of exopolymers from Gallionella ferruginea . A model is proposed for the relationship between the differences in characteristics of the iron precipitate and the kinetics of the precipitation.

Structural changes in fully hydrated Chilomonas Paramecium exposed to copper

Summary The aim of this study was to determine structural changes induced by the free copper ion in fully hydrated cells of the flagellate protozoon Chilomonas paramecium , a common inhabitant of polluted waters, and often exposed to fluctuating levels of external metals. Light microscopy showed that C. Paramecium was sensitive to copper; the cells rounded up within minutes of exposure to 2.5 mg/1 copper, and were almost spherical within 20 minutes. However, they were able to tolerate the increased copper level, and remained in this altered state for weeks. Soft X-ray microscopy showed that compartments formed and ejectosomes were released in response to initial copper exposure. All cells exposed for 28 hours had a posteriorly positioned indentation that could not be correlated to the vestibulum. Some cells had regenerated their flagella. Quantified data pertaining to changes in the pellicle width after copper exposure of live, fully hydrated cells with natural specimen contrast are given.

Significance of plasmalemma disruption in bovine and equine spermatozoa.

We have investigated fresh and cryopreserved bovine and equine spermatozoa using light and transmission soft X-ray microscopy. Spermatozoa were examined, in the presence or absence of semen, after using Percoll gradient centrifugation and re-suspending in medium. X-ray microscopy provided high resolution (30 nm) transmission images of whole cells in solution with high contrast, while retaining the simple preparation techniques used in light microscopy. We demonstrated translucent, membrane-bound vesicles in the acrosomal and midpiece regions that were similar in size and we noted their incidence in both fresh and frozen-thawed material from both animals. The vesicles were formed by the separation and expansion of the plasmalemma away from the underlying structure but were not caused by the freeze-thaw process. We suggest that these structures form part of the normal ultrastructure of spermatozoa and are damaged during preparation of the samples for transmission electron microscopy, resulting in a structure previously and incorrectly identified as damaged by the freezing and thawing process.

Al3+AND Zn2+-INDUCED STRUCTURAL CHANGES AND LOCALIZATION IN A FULLY-HYDRATED LIVE EUKARYOTIC CELLULAR MODEL

This study combined techniques that did not require preparation protocols that were potentially harmful to the cell, making it possible to investigate cells at, or close to, their natural physiological state. We used the freshwater protozoon Chilomonas paramecium as a eukaryotic cellular model to locate sites of Al3+or Zn2+accumulation and quantify the associated structural changes. Cells were fully hydrated throughout the study, which used a combination of differential interference contrast light microscopy, confocal laser scanning microscopy and transmission X‐ray microscopy. The latter technique allowed high resolution (50nm) and high contrast imaging of live cells in solution. For confocal laser scanning microscopy the relatively new fluorochrome Newport Green was used. This made fluorescent complexes with intracellular Al3+and Zn2+, allowing localisation of metal‐containing granules and vesicles. After long term exposure a previously unreported annular‐shaped site of metal accumulation was found, signifying a vesicle with metal accumulated in the periphery only. After exposure to Al3+and Zn2+, the cell pellicle was thinner and the majority of rounded‐up cells had a concentric layering of organelles. By combining a variety of techniques it was possible to gain high resolution structural and chemical information on cells minimally exposed to potentially artefact‐inducing procedures.

A new technique of examining pollen‐connecting threads

A new technique of obtaining high resolution structural information on pollen‐connecting threads is outlined. The method employs a transmission X‐ray microscope which has a resolution down to 30 nm, which is greater than a light microscope (∼ 200 nm), but retains the simplicity of sample preparation for light microscopy. The advantage of the method is that there is no requirement for extensive sample preparation. Unlike electron microscopy preparation techniques, in X‐ray microscopy there is no need for dehydration, fixation, staining or coating, and the sample is imaged at ambient pressure. Viscin threads from 9 plant species were investigated, 7 from the family Onagraceae, and two Ericaceae. It was found that in some species, structural detail complemented previously presented scanning electron microscopy images of specimens. However, in a number of species we found contrasting structures, to previous scanning electron microscopy work. It was concluded that by using X‐ray microscopy we were able to both...

X-Ray Microscopy in Aarhus

The Aarhus imaging soft X-ray microscope is now a busy multi-user facility. The optical set-up will be described and project highlights discussed. a) Metal-induced structural changes in whole cells in solution. The effects of aluminum, copper, nickel and zinc on protozoa investigated by using a combination of light microscopy, confocal scanning laser microscopy and X-ray microscopy. b) Botanical studies by X-ray microscopy used to compliment electron microscopy studies. c) Sludge morphology and iron precipitation in Danish freshwater plants by combining X-ray, scanning electron and transmission electron microscopy.

Morphological studies of human sperm using the Aarhus X-ray microscope

Using the Aarhus transmission X-ray microscope we have shown that the mitochondria of human spermatozoa can exist in two morphologically distinct states. We have also discovered new structures on the human spermatozoon surface. These structures manifest as clear vesicular bodies associated with specific membrane domains. They can occur around the acrosomal segment, the mid-piece region or at the basal region. Prior to our findings they were not described in the literature, even though they were clearly visible by light microscopy and ubiquitous among populations of sperm from fertile donors. We report on our findings and subsequent endeavours to elucidate the function of these fascinating structures.