Diel vertical migration ofEudiaptomus gracilis during a short summer period

Several aspects of a diel vertical migration (DVM) of adultEudiaptomus gracilis in Lake Maarsseveen (The Netherlands) are described. The period of DVM lasted from the end of May until the middle of August. On May 21, 1989, the population was found divided into a deep dwelling part and a part in the upper five meter. Large shoals of juvenile perch were observed in the open water for the first time. On June 7, the whole population was down below 10 m and concentrated in a zone of high chlorphyll-a concentrations. One week later, a regular DVM was performed. The amplitude of this migration gradually decreased towards the end of the migration period. The ascent in the evening and the descent in the morning took place after sunset and before sunrise, respectively. The movements coincided with high relative changes in light intensity. Population size increased rapidly during the period of DVM but decreased again before the end of this period.     

Mineralization of Trichloroethylene by Heterotrophic Enrichment Cultures

Microbial consortia capable of aerobically degrading more than 99% of exogenous trichloroethylene (TCE) (50 mg/liter) were collected from TCE-contaminated subsurface sediments and grown in enrichment cultures. TCE at concentrations greater than 300 mg/liter was not degraded, nor was TCE used by the consortia as a sole energy source. Energy sources which permitted growth included tryptone-yeast extract, methanol, methane, and propane. The optimum temperature range for growth and subsequent TCE consumption was 22 to 37°C, and the pH optimum was 7.0 to 8.1. Utilization of TCE occurred only after apparent microbial growth had ceased. The major end products recovered were hydrochloric acid and carbon dioxide. Minor products included dichloroethylene, vinylidine chloride, and, possibly, chloroform.     

Further investigations on the distribution of hibernating Culex pipiens pipiens L. (Diptera, Culicidae) in artificial marl-caves in south limburg (Netherlands)

In three artificial marl-caves in Dutch Limburg with a similar simple construction and belonging to the horizontal static type, the factors influencing the choice of the hibernation sites of Culex pipiens pipiens L. were studied.From counts made in January of the years 1958–1960 it appeared that despite differences of the caves the picture obtained for the distribution of the mosquitoes agreed markedly and, in addition, many aspects were found the same over these years.By means of a series of field experiments it was established that the factor light determines the broad outlines of the distribution of the hibernating mosquitoes in the cave corridors investigated. Measurements of light intensities showed fluctuations in intensity in the corridors of the caves investigated. Broadly speaking the mosquitoes were observed in the twilight zone. In this zone maxima in the distribution of the mosquitoes appeared to coincide with the spatial change of decrease into increase of light intensity.In a small niche in one of the caves most mosquitoes were found on the side opposite to the entrance of the cave. This phenomenon was already recognized in an earlier study on the distribution of Culex in the marl-caves of Southern Limburg (Kuchlein & Ringelberg 1956).

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Zusammenfassung In drei künstlichen Mergel-Höhlen holländisch Limburgs mit ähnlich einfachem Bau und vom gleichen horizontal statischen Typ wurden die Faktoren untersucht, welche die Wahl der Überwinterungsplätze von Culex pipiens pipiens L. beeinflussen.Zählungen, die jeweils im Januar der Jahre 1958–1960 durchgeführt wurden, erweckten den Ànschein, daß trotz der Unterschiede in den Höhlen das erhaltene Bild über die Verteilung der Stechmücken auffällig übereinstimmte und außerdem viele Aspekte während dieser Jahre gleich blieben.Mit Hilfe einer Reihe von Feldversuchen wurde festgestellt, daß der Faktor Licht die groben Züge der Verteilung der überwinternden Mücken in den untersuchten Höhlengängen bestimmt. Messungen der Lichtintensitäten ergaben Schwankungen der Stärke in den geprüften Höhlenkorridoren. Grob gesagt wurden die Stechmücken in der Zwielicht-Zone gefunden. In dieser Zone scheinen die Maxima der Stechmückenverteilung mit dem räumlichen Umschlag von Abnahme zu Zunahme der Lichtintensität zusammenzufallen.In einer kleinen Nische in einer der Höhlen wurden die meisten Mücken auf der dem Eingang gegenüberliegenden Seite der Höhle gefunden. Dieses Phänomen wurde bereits in einer früheren Untersuchung über die Verteilung von Culex in den Mergel-Höhlen Süd-Limburgs (Kuchlein & Ringelberg 1956) behandelt.

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Validation of signature polarlipid fatty acid biomarkers for alkane-utilizing bacteria in soils and subsurface aquifer materials

Abstract Extractable cell membrane-derived polarlipid ester-linked fatty acids (PLFA) obtained from aerated soils gassed with methane or propane and from methane- and propane-oxidizing bacteria isolated from the soils were analyzed by capillary gas chromatography/mass spectrometry. Exposure of aerated soils to methane resulted in the formation of a high proportion of an unusual 18-carbon mono-unsaturated PLFA, 18:lw8c. High proportions of this fatty acid biomarker are found in monocultures from this soil grown in minimal media with methane. This PLFA has been previously established as associated with authentic type II methane-oxidizing bacteria. The microbiota in aerated soils exposed to hydrocarbons containing propane, formed a suite of PLFA characterized by high proportions of a 16-carbon mono-unsaturated acid, 16:lw6c, and an 18-carbon saturated fatty acid with an additional methyl branch at the 10 position, 10 Me 18:0. This PLFA pattern has been detected in several monocultures enriched from the soil with propane-amended minimal media. The correspondence of high proportions of these unusual mono-unsaturated PLFA in the isolated monocultures and in situ in the soils after stimulation with the appropriate hydrocarbon is a strong validation of the utility of these biomarkers in defining the community structure of the surface soil microbial community.     

Daphnids respond to algae-associated odours

Using a Y-tube olfactometer, it was found that Daphnia galeatax hyalina moves to the arm with odour from either of two ediblealgal species (Scenedesmus acuminatus and Oscillatoria limnetica)rather than to the alternative arm with clean water. However,no differential response was observed when odours of the toxiccyanobacterium (Oscillatoria agardhu) were tested. We suggestthat odours associated with edible algae attract Daphnia whereasnon-edible algae do not elicit attraction of Daphnia.     

Comparison of phylogenetic relationships based on phospholipid fatty acid profiles and ribosomal RNA sequence similarities among dissimilatory sulfate-reducing bacteria

Abstract Twenty-five isolates of dissimilatory sulfate-reducing bacteria were clustered based on similarity analysis of their phospholipid ester-linked fatty acids (PLFA). Of these, 22 showed that phylogenetic relationships based on the sequence similarity of their 16S rRNA directly paralleled the PLFA relationships. Desulfobacter latus and Desulfobacter curvatus grouped with the other Desulfobacter spp. by 16S rRNA comparison but not with the PLFA analysis as they contained significantly more monoenoic PLFA than the others. Similarly, Desulfovibrio africanus clustered with the Desulfovibrio spp. by 16S rRNA but not with them when analyzed by PLFA patterns because of higher monoenoic PLFA content. Otherwise, clustering obtained with either analysis was essentially congruent. The relationships defined by PLFA patterns appeared robust to shifts in nutrients and terminal electron acceptors. Additional analyses utilizing the lipopolysaccharide-lipid A hydroxy fatty acid patterns appeared not to shift the relationships based on PLFA significantly except when completely absent, as in Gram-positive bacteria. Phylogenetic relationships between isolates defined by 16S rRNA sequence divergence represent a selection clearly different from the multi-enzyme activities responsible for the PLFA patterns. Determination of bacterial relationships based on different selective pressures for various cellular components provides more clues to evolutionary history leading to a more rational nomenclature.     

Differential life history responses of several pelagic Daphnia clones differing in migratory behaviour

Females of the hybrid Daphnia galeata × hyalina were isolated from a natural population in Lake Maarsseveen and from these individuals clones were cultured in the laboratory. Some clones were assumed to be migrating and some non-migrating. Life history experiments were performed with these clones in the presence and absence of fish kairomones. Results show that clones differed in life history strategy in concert with their presumed migration strategies which suggests a link between life history and behaviour. However, no sharp border exists between migrating and non-migrating clones since a gradual response pattern was found for the traits investigated. In the absence of fish kairomones, the relation between length at maturity and number of eggs was found to differ between the clones of the non-migrating and the migrating group. The latter had a lower number of eggs at similar length values. In the presence of fish kairomones, the length–clutch size relation was the same. However, non-migrating clones were smaller at the age at maturity and had fewer eggs. Although clones of both groups were thus found to differ significantly, overlap existed. Age at maturity was found to be the same.