High frequency electric fields for trapping of viruses

Summary Combining dielectrophoretic and hydrodynamic forces in micro electrode structures allows enrichment and stable trapping of viruses in aqueous solutions. Fluorescently labelled Influenza and Sendai viruses were collected from solutions of 2^*10⁵ – 2^*10⁸ viruses/l within a few seconds. In the central part of the trap a virus aggregate of about 2–9 m in diameter was formed. This corresponds to a local enrichment of viruses up to a factor of about 1400.     

Gymnodinium catenatum Graham (Dinophyceae)in Europe: a growing problem?

The microreticulate resting cyst of the potentially toxic, chain-forming,unarmoured neritic dinoflagellate Gymnodinium catenalum Graham1943. the planktonic stage of which is not known from NorthEuropean waters, is reported for the first time from recentGerman coastal sediments of the North Sea and Baltic Sea. Insandy mud sediments of the German Bight, a maximum of 8 5 livingcysts cm^–3 were found. In Kiel Bight sediments G.catenalumwas found in maximum concentrations of 17.0 living cysts cm^–3.In surface waters of the German Bight resuspended G catenatumcysts were observed at concentrations of up to 3.6 cysts l^–1.Successful germination experiments conducted with natural seawatershow that the occurrence of a vegetative form of G.catenatumin northern Europe is very likely. The present study highlightsthat cyst surveys provide an important tool for the evaluationof areas with potential toxicity problems, as they may indicatethe presence of hitherto overlooked species in the water column.     

Functional analysis of the iron-stress induced CP 43′ polypeptide of PS II in the cyanobacterium Synechococcus sp. PCC 7942

Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43 apoprotein (designated isiA ^–) and (ii) flavodoxin (designated isiB ^–). The function of CP 43 was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA ^– and isiB ^– strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43 and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43 is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB ^– strain grown under iron-deficient conditions, CP 43 was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (F_o) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.Abbreviations Chl chlorophyll - CP 43, CP 47 and CP 43 Chl a binding protein complexes of indicated molecular mass - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F_m and F_m fluorescence when all PS II reaction centers are dosed in dark- and light-acclimated cells, respectively - F_o fluorescence when all PS II reaction centers are open in dark acclimated cells - F_v variable fluorescence after dark acclimation (F_m–F_o)     

Feeding biology of two brachionid rotifers: Brachionus quadridentatus and Brachionus plicatilis

Brachionus quadridentatus and Brachionus plicatilis were examined in laboratory cultures to investigate their (1) food requirements and (2) ability to select particles on the basis of size. Growth experiments showed that the Chlorophyceans Nannochloris sp. and Chlorella vulgaris possess good nutritional value for these rotifers. However, B. quadridentatus declined in cultures with Microcystis firma, detritus of Enteromorpha sp. or Pseudomonas sp. (bacteria) as a sole source of food, thus indicating that these foods were inadequate. Utilization of latex microspheres by these two species indicate that they respond to particle size in different ways: B. quadridentatus had a higher selectivity index for 3 and 5 µm beads, while B. plicatilis had a higher selectivity index for 2 µm beads.     

Twintrons are not unique to the Euglena chloroplast genome: structure and evolution of a plastome cpn60 gene from a cryptomonad

Introns within introns (twintrons) are known only from the Euglena chloroplast genome. Twintrons are group II or III introns, into which another group II or III intron has been transposed. In this paper we describe a non-Euglena twintron structure within a plastid-encoded chaperone gene (cpn60) of the cryptomonad alga Pyrenomonas salina. In addition, the evolutionary relationships between members of the Cpn60 protein family are determined. Our findings permit the inclusion of cryptomonad plastomes in phylogenetic studies of intron evolution and present further evidence for the origin of modern plastids from a cyanobacterial ancestor.This paper is dedicated to Prof. Dr. Peter Sitte on the occasion of his 65th birthday     

Isolation of early genes expressed in reproductive organs of the dioecious white campion (Silene latifolia) by subtraction cloning using an asexual mutant

The dioecious white campion (Silene latifolia) has been chosen as a working model for sexual development. In this species, sexual dimorphism is achieved through two distinct developmental blocks: inhibition of carpel development in male flowers, and early arrest of anther differentiation in female flowers. The combined advantages of the dioecious system and the availability of a sexual mutant lacking both male and female reproductive organs have been exploited in a molecular subtraction approach using male and asexual flower buds. This resulted in the cloning of 22 cDNA clones expressed in stamens at distinct stages of development. Fourteen of these clones corresponded to genes whose expression was detected in pre-meiotic stamens, a stage of development for which very little information is presently available. Furthermore, the absence of similarities with database sequences for ten clones suggests that they represent novel genes. Functional analysis of each clone will enable their positioning within the reproductive organ developmental pathway(s). In parallel, these clones are being exploited as developmental markers of early differentiation within the flower.     

Domain Evolution in the α-Amylase Family

The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their domain B, a distinct domain that protrudes from the regular catalytic (β/α)₈-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase, cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable similarity with (β/α)₈-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family. Received: 4 December 1996 / Accepted: 13 March 1997