Microbial mats and physicochemistry in a saltern in the Bretagne (France) and in a laboratory scale saltern model

Abstract A saltern near La Baule (Bretagne, France) was remodeled in a programmable temperature and humidity controlled walk-in environmental chamber resembling the characteristics of the original saltern. The saltern showed different types of microbial mats predominantly composed of algae, oxy- and anoxyphotobacteria, and associated chemoorganotrophic bacteria, fungi and animals. Well-developed microbial mats were found up to a salinity of 10% during the three or four months in summer when salinity gradients and NaCl precipitation were established. The main phototrophic organisms were diatoms, the cyanobacteria Aphanothece, Microcoleus, Spirulina , and Oscillatoria , and Chromatiaceae. At higher salinity, Halobacterium sp., diatoms, and Dunaliella were dominant. Typical microbial mats and saltern-typical invertebrate, algal and bacterial species also developed in the saltern model, building up a stable community. The ionic composition of the brines and physicochemical parameters were similar to those determined for the original saltern. Different photosynthetic organisms, e.g. a filamentous purple bacterium and a hypersaline Chloroflexus -like organism, could be enriched within the microbial mats by changing the light regime.     

A microdeletion of less than 250 kb, including the proximal part of the FMR-1 gene and the fragile-X site, in a male with the clinical phenotype of fragile-X syndrome

A gene designated "FMR-1" has been isolated at the fragile-X locus. One exon of this gene is carried on a 5.1-kb EcoRI fragment that exhibits length variation in fragile-X patients because of amplification of or insertion into a CGG-repeat sequence. This repeat probably represents the fragile site. The EcoRI fragment also includes an HTF island that is hypermethylated in fragile-X patients showing absence of FMR-1 mRNA. In this paper, we present further evidence that the FMR-1 gene is involved in the clinical manifestation of the fragile-X syndrome and also in the expression of the cellular phenotype. A deletion including the HTF island and exons of the FMR-1 gene was detected in a fragile X-negative mentally retarded male who presented the clinical phenotype of the fragile-X syndrome. The deletion involves less than 250 kb of genomic DNA, including DXS548 and at least five exons of the FMR-1 gene. These data support the hypothesis that loss of function of the FMR-1 gene leads to the clinical phenotype of the fragile-X syndrome. In the fragile-X syndrome, there are pathogenetic mechanisms other than amplification of the CGG repeat that do have the same phenotypic consequences.     

Prey selection of the shallow water fishPomatoschistus minutus (Gobiidae,Teleostei) in the SW Baltic

The aim of this investigation is to demonstrate the reasons of an opportunist feeder to select some components of the available food supply and to avoid others. Object of this test is the eurytopic and euryhaline sand goby,Pomatoschistus minutus (Pallas), from the Luebeck Bight. It inhabits both sand habitats as well as bottoms mixed with pebbles or continuous hard substrates. Therefore, it is often in close contact withMytilus-belts which present a very rich food supply of small crustaceans. The selectivity behaviour of sand gobies from a sand/clay ecotone was compared with that of populations from a stony pier and a sand bottom during the reproduction period. Regarding the numbers of prey organisms, crustaceans of the periphyton were generally preferred at the pier but avoided in the ecotone. The same is valid for prey organisms of the psammal which were preferred by gobies of the sand bottom but mostly avoided by populations of mixed bottoms. Analyses of size selections revealed that the preferred gammarids orJaera isopods were between 2 and 5 mm length. A balanced relation of goby biomass and utilizable food supply (predatory impact index) seems to effect positive selectivity of gammarids in theMytilus-belts or of harpacticoids in the sand bottom.     

Regulation of Ca2+-activated K+ Channel from Rabbit Distal Colon Epithelium by Phosphorylation and Dephosphorylation

The Ca²⁺-activated maxi K⁺ channel is predominant in the basolateral membrane of the surface cells in the distal colon. It may play a role in the regulation of the aldosterone-stimulated Na⁺ reabsorption from the intestinal lumen. Previous measurements of these basolateral K⁺ channels in planar lipid bilayers and in plasma membrane vesicles have shown a very high sensitivity to Ca²⁺ with a K _0.5 ranging from 20 nm to 300 nm, whereas other studies have a much lower sensitivity to Ca²⁺. To investigate whether this difference could be due to modulation by second messenger systems, the effect of phosphorylation and dephosphorylation was examined. After addition of phosphatase, the K⁺ channels lost their high sensitivity to Ca²⁺, yet they could still be activated by high concentrations of Ca²⁺ (10 μm). Furthermore, the high sensitivity to Ca²⁺ could be restored after phosphorylation catalyzed by a cAMP dependent protein kinase. There was no effect of addition of protein kinase C. In agreement with the involvement of enzymatic processes, lag periods of 30–120 sec for dephosphorylation and of 10–280 sec for phosphorylation were observed. The phosphorylation state of the channel did not influence the single channel conductance. The results demonstrate that the high sensitivity to Ca²⁺ of the maxi K⁺ channel from rabbit distal colon is a property of the phosphorylated form of the channel protein, and that the difference in Ca²⁺ sensitivity between the dephosphorylated and phosphorylated forms of the channel protein is more than one order of magnitude. The variety in Ca²⁺ sensitivities for maxi K⁺ channels from tissue to tissue and from different studies on the same tissue could be due to modification by second messenger systems. Received: 28 February 1995/Revised: 22 December 1995     

Approximate digestibility of fibre for a graminivorous caterpillar

Final instar Persectania ewingii (Westwood) (Lepidoptera: Noctuidae) were fed seedling Triticum aestivum L. for 2 days to determine the approximate digestibility of the cell wall and cell content fractions. Cell wall content was estimated using a micro-analytical neutral detergent fibre technique. Approximate digestibilites of neutral detergent fibre, neutral detergent solubles and dry matter were calculated for individuals and pooled samples. P. ewingii larvae digested a small but significant proportion of the fibre ingested (13–21%), higher than that previously reported for herbivorous insects. The micro-analytical and previously used macro-analytical techniques produced similar estimates of digestibility although both techniques have inherent shortcomings, the latter requiring the pooling of samplex and the former limiting the number of replicates during chemical analysis. Differences in the amount of larval frass collected during the feeding trial (corrected for consumption) explained much of the variation in digestibility values, while there were no effects of larval mass, overall consumption and total frass produced on digestibility estimates. These results confirm that plant cell contents are the major source of nutrients to larval Lepidoptera although there is some chemical disruption of the plant cell wall.     

Taxonomic identification of Streptomyces exfoliatus K10 and characterization of its poly(3-hydroxybutyrate) depolymerase gene

Abstract Using fungi grown on synthetic agar medium, we evaluated and compared the concentration of various H₂O₂-producing enzymes. Our results showed that oxidase production in solid medium was better than that found in liquid medium and as high as that detected in wood samples. High yields of oxidases made it possible to compare different oxidases in the same culture extracts and under different conditions. Our results also indicated that H₂O₂ production is ubiquitous in the white rot fungi tested and that enzyme levels are influenced by the substrate composition.     

CAM variations in the leaf-succulent Delosperma tradescantioides (Mesembryanthemaceae), native to southern Africa

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (∼ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C₃ gas exchanges when well-watered to water-conserving CAM-idling during drought.