Structure-activity relationships of epoxides: induction of sister-chromatid exchanges in Chinese hamster V79 cells

Analysis of SCE frequencies in Chinese hamster V79 cells was used to investigate structure-activity relationships of epoxides in mammalian cells. For this purpose the SCE-inducing potency of 58 epoxides was determined. Of these, 16 failed to induce SCE in V79 cells. According to the substitution of the oxirane ring the results show general agreement with results obtained in the Ames test. Mono-substituted epoxides had the highest genotoxic potency compared to di- and tri-substituted epoxides. In detail, there are differences in genotoxic potency between bacteria and mammalian cells which can be explained by differences in the cellular uptake of the compounds and by detoxification reactions.     

Ecosystem thresholds with hypoxia

Hypoxia is one of the common effects of eutrophication in coastal marine ecosystems and is becoming an increasingly prevalent problem worldwide. The causes of hypoxia are associated with excess nutrient inputs from both point and non-point sources, although the response of coastal marine ecosystems is strongly modulated by physical processes such as stratification and mixing. Changes in climate, particularly temperature, may also affect the susceptibility of coastal marine ecosystems to hypoxia. Hypoxia is a particularly severe disturbance because it causes death of biota and catastrophic changes in the ecosystem. Bottom water oxygen deficiency not only influences the habitat of living resources but also the biogeochemical processes that control nutrient concentrations in the water column. Increased phosphorus fluxes from sediments into overlying waters occur with hypoxia. In addition, reductions in the ability of ecosystems to remove nitrogen through denitrification and anaerobic ammonium oxidation may be related to hypoxia and could lead to acceleration in the rate of eutrophication. Three large coastal marine ecosystems (Chesapeake Bay, Northern Gulf of Mexico, and Danish Straits) all demonstrate thresholds whereby repeated hypoxic events have led to an increase in susceptibility of further hypoxia and accelerated eutrophication. Once hypoxia occurs, reoccurrence is likely and may be difficult to reverse. Therefore, elucidating ecosystem thresholds of hypoxia and linking them to nutrient inputs are necessary for the management of coastal marine ecosystems. Finally, projected increases in warming show an increase in the susceptibility of coastal marine ecosystems to hypoxia such that hypoxia will expand. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Visual clone identification of Penicillium commune isolates

A method for visual clone identification of Penicillium commune isolates was developed. The method is based on images of fungal colonies acquired after growth on a standard medium and involves a high degree of objectivity, which in future studies will make it possible for non-experts to perform a qualified identification of different species as well as clones within a species. A total of 77 P. commune isolates from a cheese dairy were 3-point inoculated on Yeast Extract Sucrose (YES) agar and incubated for 7 days at 25 degrees C. After incubation, the isolates were classified into groups containing the same genotype determined by DNA fingerprinting (AFLP). Each genotype also has a specific phenotype such as different colony colours. By careful image acquisition, colours were measured in a reproducible way. Prior to image analysis, each image was corrected with respect to colour, geometry and self-illumination, thereby gaining a set of directly comparable images. A method for automatic extraction of a given number of concentric regions was used. Using the positions of the regions, a number of relevant features--capturing colour and colour-texture from the surface of the fungal colonies--was extracted for further analysis. We introduced the Jeffreys-Matusitas (JM) distance between the feature distributions to express the similarity between regions in two colonies, and to evaluate the overall (weighted) similarity. The nearest neighbour (NN) classification rule was used. On a dataset from 137 isolates, we obtained a "leave-one-out" cross-validation identification rate of approximately 93-98% compared with the result of DNA fingerprinting.     

Structure-activity relationships of epoxides: induction of sister-chromatid exchanges in V79 cells by enantiomeric epoxides.

Analysis of SCE frequencies in Chinese hamster V79 cells was used to investigate the influence of the stereoisomeric forms of epoxides in mammalian genotoxicity tests. The SCE-inducing potency of 12 pairs of (R)- and (S)-enantiomeric epoxides which differed in the degree of substitution of the oxirane ring was determined. Of these, 2 pairs of epoxides failed to induce SCE. Different SCE-inducing potencies between the (R)- and (S)-enantiomers were shown for 5 epoxides. This study demonstrates that stereoselectivity might play an important role in genotoxicity testing of chemicals with asymmetric C atoms.     

Direct identification of pure Penicillium species using image analysis

This paper presents a method for direct identification of fungal species solely by means of digital image analysis of colonies as seen after growth on a standard medium. The method described is completely automated and hence objective once digital images of the reference fungi have been established. Using a digital image it is possible to extract precise information from the surface of the fungal colony. This includes color distribution, colony dimensions and texture measurements. For fungal identification, this is normally done by visual observation that often results in a very subjective data recording. Isolates of nine different species of the genus Penicillium have been selected for the purpose. After incubation for 7 days, the fungal colonies are digitized using a very accurate digital camera. Prior to the image analysis each image is corrected for self-illumination, thereby gaining a set of directly corresponding images with respect to illumination. A Windows application has been developed to locate the position and size of up to three colonies in the digitized image. Using the estimated positions and sizes of the colonies, a number of relevant features can be extracted for further analysis. The method used to determine the position of the colonies will be covered as well as the feature selection. The texture measurements of colonies of the nine species were analyzed and a clustering of the data into the correct species was confirmed. This indicates that it is indeed possible to identify a given colony merely by macromorphological features. A classifier (in the normal distribution) based on measurements of 151 colonies incubated on yeast extract sucrose agar (YES) was used to discriminate between the species. This resulted in a correct classification rate of 100% when used on the training set and 96% using cross-validation. The same methods applied to 194 colonies incubated on Czapek yeast extract agar (CYA) resulted in a correct classification rate of 98% on the training set and 71% using cross-validation.     

Diagnostic insonation of extra utero human placentas: No effect of lymphocytic sister chromatid exchange

Summary Freshly delivered human placentas were exposed to ultrasound for 30 min using a diagnostic linear array unit. Blood was then drawn and cultured in the presence of bromodeoxyuridine, and the frequencies of sister chromatid exchanges (SCE) in the lymphocytes determined. There was no statistically significant difference in SCE frequencies between control and exposed cells; the frequencies of SCEs per cell ranged from 4.50 to 6.02 for control and from 4.66 to 6.10 for exposed cells in five separate experiments. Positive control mitomycin C treated cells were significantly affected, with more than 50 SCEs per cell.     

Beta Diversity of Plant-Pollinator Networks and the Spatial Turnover of Pairwise Interactions

Interactions between species form complex networks that vary across space and time. Even without spatial or temporal constraints mutualistic pairwise interactions may vary, or rewire, across space but this variability is not well understood. Here, we quantify the beta diversity of species and interactions and test factors influencing the probability of turnover of pairwise interactions across space. We ask: 1) whether beta diversity of plants, pollinators, and interactions follow a similar trend across space, and 2) which interaction properties and site characteristics are related to the probability of turnover of pairwise interactions. Geographical distance was positively correlated with plant and interaction beta diversity. We find that locally frequent interactions are more consistent across space and that local flower abundance is important for the realization of pairwise interactions. While the identity of pairwise interactions is highly variable across space, some species-pairs form interactions that are locally frequent and spatially consistent. Such interactions represent cornerstones of interacting communities and deserve special attention from ecologists and conservation planners alike.     

In situ cell retention of a CHO culture by a reverse‐flow diafiltration membrane bioreactor

Heterogeneities occur in various bioreactor designs including cell retention devices. Whereas in external devices changing environmental conditions cannot be prevented, cells are retained in their optimal environment in internal devices. Conventional reverse‐flow diafiltration utilizes an internal membrane device, but pulsed feeding causes temporal heterogeneities. In this study, the influence of conventional reverse‐flow diafiltration on the yeast Hansenula polymorpha is investigated. Alternating 180 s of feeding with 360 s of non‐feeding at a dilution rate of 0.2 h^?1 results in an oscillating DOT signal with an amplitude of 60%. Thereby, induced short‐term oxygen limitations result in the formation of ethanol and a reduced product concentration of 25%. This effect is enforced at increased dilution rate. To overcome this cyclic problem, sequential operation of three membranes is introduced. Thus, quasi‐continuous feeding is achieved reducing the oscillation of the DOT signal to an amplitude of 20% and 40% for a dilution rate of 0.2 h^?1 and 0.5 h^?1, respectively. Fermentation conditions characterized by complete absence of oxygen limitation and without formation of overflow metabolites could be obtained for dilution rates from 0.1 h^?1 – 0.5 h^?1. Thus, sequential operation of three membranes minimizes oscillations in the DOT signal providing a nearly homogenous culture over time. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1348–1355, 2014