The particle size characteristics of fluvial suspended sediment: an overview

The particle size characteristics of suspended sediment are of fundamental importance in understanding its role in a variety of environmental processes. Existing knowledge concerning the spatial and temporal variability of the grain size composition of suspended sediment is, however, relatively limited. At the global scale, major contrasts may exist between individual rivers in the calibre of their suspended load and this may be related to a number of controls including climate, catchment geology and basin scale. Any attempt to understand the precise relationship between the grain size characteristics of suspended sediment and those of its source material must also take account of the selectivity of erosion and delivery processes. A local case study undertaken by the authors in the 1500 km² basin of the River Exe in Devon, UK is used to illustrate the considerable spatial variability that may occur within a relatively small area and the complexity of the associated controls.Available evidence concerning the temporal variability of the grain size characteristics of suspended sediment emphasises the diverse patterns of behaviour that may exist and the complexity of the controls involved. In some rivers the sediment may become coarser as flow increases, in others it may become finer, whilst in others it may exhibit a relatively constant grain size composition. Data from the local case study in the Exe basin are again used to highlight the considerable diversity in response to changing discharge that may occur within a relatively small area.Any attempt to understand the dynamics of sediment movement through a river system must also take account of the potential contrast between the ultimate and effective particle size distribution of suspended sediment in response to aggregation. Results from the Exe basin study indicate that even in rivers with relatively low solute concentrations, almost an order of magnitude difference may exist between the median particle size associated with the ultimate and effective grain size distributions.     

Use of the polymerase chain reaction to identify mosquito species of the Anopheles gambiae complex

A nonradiometric method has been developed for distinguishing between the sibling species Anopheles gambiae Giles and An. arabiensis Patton, two important Afrotropical vectors of malaria. DNA fragments of species diagnostic length are amplified by polymerase chain reaction (PCR) from a small amount of unknown DNA and three different PCR primers. All three PCR primers are based on ribosomal DNA (rDNA) sequences. A universal plus-strand primer (A0) is derived from a conserved region at the 3' end of the 28S rDNA coding region. Two species-specific minus-strand primers (Aa0.5 and Ag1.3) are derived from sequences in the intergenic spacers. The Ag1.3 sequence is approximately 1.3 kb downstream of A0; the Aa0.5 sequence is about 0.5 kb downstream of A0. When mosquito DNA is amplified in the presence of all three primers, a 1.3 kb fragment is produced if An. gambiae DNA is used as template, and a 0.5 kb fragment is produced if An. arabiensis DNA is used. Amplification of DNA from An.gambiae/An. arabiensis hybrids produces both the 1.3 kb and the 0.5 kb fragments. Neither diagnostic fragment is produced when DNA from other species in the An. gambiae complex is used as template.     

Experimental pulmonary candidiasis

The initial interaction of Candida albicans with pulmonary tissue of B6D2/F₁ mice was investigated. The LD₅₀ for mice challenged intravenously (IV) was approximately 3 × 10⁵ yeasts, whereas the LD₅₀ by the intratracheal (IT) route was in excess of 10⁸ yeasts. Mice challenged IV died of progressive yeast growth in the kidneys. In contrast, mice challenged IT rapidly eliminated the entire inoculum by the first day after challenge. Resident pulmonary alveolar macrophages (PAM) killed upwards of 70% of C. albicans in an in vitro killing assay. At effector: target ratios favoring the effector cell population resident PAM were able to restrict the formation of yeast germ tubes to only 30% of the yeasts, whereas at equivalent ratios virtually all of the intracellular yeasts produced germ tubes. Evaluation of the ability of PAM, harvested from genetically different strains of inbred mice, to kill C. albicans in vitro showed that killing ability was a property of resident PAM from mice with the black 6 background. It was discovered that during the initial stages of infection in vivo, the expression of the F4/80 surface molecule was down regulated, and the expression of the Mac 1 surface molecule upregulated. There were no quantitative changes in expression of either Mac 2, Mac 3, Ly 5 or the 5C6 surface epitopes. Taken together, the data show that pulmonary tissue is quantitatively very resistant to C. albicans infection, because of the ability of resident PAM to rapidly phagocytize and kill yeasts. Killing of C. albicans by resident PAM may be a property of a subset of this mononuclear phagocyte population and was accompanied by alterations in the expression of surface molecules.Presented as part of the Everett S. Beneke Symposium in Mycology, May 27, 1988.     

Molecular cloning and expression of a proteinase gene from Lactococcus lactis subsp. cremoris H2 and construction of a new lactococcal vector pFX1

The 6.5 kb HindIII DNA fragment of the Lactococcus lactis subsp. cremoris H2 plasmid pDI21 was cloned into Escherichia coli POP13 with NM1149, and also directly into Lactococcus lactis subsp. lactis 4125 using a newly-constructed broad host-range vector pFX1. Proteinase was experessed in both transformed organisms. The proteinase resembles a PI type since it preferentially degraded -casein. The restriction map of the 6.5 kb proteinase gene fragment has minor differences from those of published plamid proteinase genes. High-efficiency electroporation with pFX1 provides a direct approach for gene cloning in lactococci.Abbreviations cfu colony forming units - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] Dedicated to Prof. Dr. G. Drews on the occasion of his 65th birthday     

Underwater observations of piranhas in western Brazil

Synopsis The behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.     

A practical test for in vitro evaluation of photosensitization: Assessment with hematoporphyrin derivative (HPD)

A simple procedure is described for the determination of the photosensitizing potency of drugs, using three leukemic cell lines, two of lymphocytic origin, L1210 and P388 and one of erythroid type, Friend-745. The procedure allows one to investigate several aspects of the photosensitization properties of tested compounds such as cellular localization and direct (trypan blue exclusion) or delayed (clonogenicity) photomediated toxicities.The method was assessed using crude hematoporphyrin derivative (HPD) as well as dihematoporphyrin ether (DHE) or commercially available Photofrin II. Results were compared to those obtained with normal cells, e.g spleen lymphocytes and erythropoietic stem cells (CFU-e), and discussed in the light of the relative response of normal versus transformed cells.Abbreviations DHE Dihematoporphyrin Ether - FCS Fetal Calf Serum - HPD Hematoporphyrin Derivative - PDT Photodynamic Therapy     

Structural studies of nerve terminals containing melanin-concentrating hormone in the eel,Anguilla anguilla

Summary Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120×90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.     

Functional and spectral characterization of the respiratory chain of Chloroflexus aurantiacus grown in the dark under oxygen-saturated conditions

In this paper we attempt a functional and spectral characterization of the membrane-bound cytochromes involved in respiratory electron transport by membranes from cells of Chloroflexus aurantiacus grown in the dark under oxygen saturated conditions. We conclude that the NADH-dependent respiration is carried out by a branched respiratory chain leading to two oxidases which differ in sensitivity to CN^- and CO. The two routes also show a different sensitivity to the ubiquinone analogue, HQNO, the pathway through the cytochrome c oxidase being fully blocked by 5 M HQNO, whereas the alternative one is insensitive to this inhibitor. The cytochrome c oxidase containing branch is composed by at least two c-type haems with E _m 7.0 of +130 and +270 mV ( bands at 550/553 nm and 549 nm, respectively), plus a b-type cytochrome with E _m 7.0 of +50 mV ( band at 561 nm). From this, and previous work, we conclude that respiratory and photosynthetic electron transport components are assembled together and function on a single undifferentiated plasma membrane.Abbreviations HQNO heptylhydroxy-quinoline-N-oxide - UHDBT undecyl-hydroxydioxobenthiazole - Q/b-c ubiquinol/cytochrome c oxidoreductase complex - BChl bacteriochlorophyll     

Interactions of piperidine derivatives with the nicotinic cholinergic receptor complex from Torpedo electric organ

The interactions of eight piperidine derivatives with nicotinic receptor complexes fromTorpedo californica electric organ were studied using [¹²⁵I]alpha-bungarotoxin ([¹²⁵I]BGT) as a probe for the acetylcholine binding site and [³H]perhydrohistrionicotoxin ([³H]H₁₂-HTX) as a probe for a site associated with the receptor-gated ion channel.Cis- andtrans-2-methyl-6-n-undecanyl piperidines (MUP), major constituents of fire ant venom, had a high-affinity for [³H]H₁₂-HTX binding sites (K_i=0.08–0.24 M), but had no affect on receptor binding. MUP affinity for [³H]H₁₂-HTX binding sites was approximately doubled in the presence of 1 M carbamylcholine. Introduction of a 2-hydroxyl group to the undecanyl side channel had little effect on activity of the alkaloid. The analog 2,6- (but not 3,5-) dimethylpiperidine was a moderately active inhibitor of [³H]H₁₂-HTX binding (K _i-8.8 M). 2-Methylpiperidine was considerably less active (K _i=600 M), although it was more potent than either 3- or 4-methylpiperidine. The affinities of 2,6-dimethylpiperidine and 2-methylpiperidine for [³H]H₁₂-HTX binding sites were decreased in the presence of 1 M carbamylcholine. Carbamylcholine affinity for the receptor was increased by up to 7 fold in the presence of 10 and 32 M MUP, but was decreased in the presence of 2,6-dimethylpiperidine and 2-methylpiperidine. Thecis- andtrans-isomers of MUP were equipotent in producing each of its effects. In these actions, MUP resembles a variety of other compounds derived from 2,6-disubstituted piperidines, including histrionicotoxins, gephyrotoxins and pumiliotoxins. These studies establish the importance of alkyl substitutions in theortho position of the piperidine ring in conferring ion channel specificity, and the importance of substantial alkyl side chains in conferring the ability of channel blockers to stabilize the nicotinic receptor complex in high affinity, desensitized conformations.