Spatial patterns and feeding of meiobenthic harpacticoid copepods in relation to resident microbial flora

Distributional and feeding relationships of harpacticoid copepods and their microbial prey were examined in a tidal channel at Great Sippewissett Marsh. A horizontal zonation of photosynthetic microorganisms was composed of: 1) a diatom area; 2) a purple sulfur bacterial (Thiocapsa sp.) area; and 3) a clear area. Four species of harpacticoid copepods were associated with given areas. Leptocaris brevicornis occurred in very high densities in the diatom area but in relatively low densities in other areas. Mesochra lilljeborgi occurred in significantly higher densities in the purple and clear areas.Feeding experiments, using resident microbial flora labelled with NaH¹⁴CO₃ and ³H-thymidine, were conducted to determine which foods are 1) ingested but simply pass through the gut and 2) ingested, and retained. These experiments indicated that L. brevicornis ingested diatoms and the heterotrophs associated with the diatoms, but only retained the heterotrophic portion. Microscopic examination indicated that diatoms were passed out intact in feces. Oscillatoria sp. (cyanobacterium) was not ingested. Mesochra lilljeborgi ingested Spirulina sp. (cyanobacterium), Thiocapsa sp., and the heterotrophs associated with Thiocapsa but only retained the Thiocapsa label.These data for harpacticoids suggest that spatial distributions of meiofauna may be closely coupled with microbial food organisms which they consume. Also, that while several microbial foods may be ingested, only certain microbes are digested and assimilated as a food resource, further indicating the complexity of feeding relationships among the meiofauna.     

Semicontinuous and Continuous Production of Chloroperoxidase by Caldariomyces fumago Immobilized in k-Carrageenan

Three strains of Caldariomyces fumago were immobilized in 4% k-carrageenan and tested for semicontinuous production of chloroperoxidase (CPO). Over an 80-day period, growing in defined medium, C. fumago strains CMI 89362 and ATCC 11925 produced enzyme concentrations of 99 and 71 mg/liter, respectively, during six production periods of 12 to 14 days, while C. fumago DAOM 137632 produced only 24 mg of CPO per liter during six growth periods of 10 days. CPO production was unaffected by various regimens of washing between transfers. Mycelial growth was primarily restricted to the head surface, and bead size increased linearly with time. Attempts to restrict growth but maintain CPO production were unsuccessful. Pigment production, fructose utilization, and pH change in the immobilized cell cultures compared closely with the growth characteristics of free cell cultures. By using an airlift tower fermentor with an external loop run with continuous medium replacement of 20 ml/h (D = 0.016), strain CMI 89362 in bead form produced CPO at 40 mg/liter for 11 days.     

EFFECT OF TREE CANOPY REMOVAL BY GYPSY MOTH LARVAE ON THE MACROALGAE OF A RHODE ISLAND HEADWATER STREAM1

A spring-fed, headwater stream in central Rhode Island was examined during the period from June to October, 1979 to 1982. In the first two summers, a dense riparian canopy reduced the light penetration at the stream surface to a range of 5 to 18% of incident radiation. The lotic macroalgal community during this period was limited to 1 to 4 species covering < 1 to 35% of the stream bottom. However, in June and July, 1981, the surrounding leaf canopy was removed by a massive gypsy moth larval outbreak. Light penetration to the stream during this summer increased to 73% by early July, thereby resulting in a rise in water temperatures by 3.7°C. Even though there was a partial regrowth of leaves in late July and August of 1981, macroalgal cover values continued to rise to an early August peak of 80%. During the third summer, 88% of the macroalgal abundance could be attributed to illumination and water temperature. The filamentous diatom Funotia pectinalis ( O.F. Müll.) Rabh. was the predominant species in the midsummer of all four years, accounting for at least 60% of the total cover. In 1981. an important taxon was the desmid Hyalotheca dissiliens (S. Smith) Bréb., a species which was not seen in other years. A less severe gypsy moth defoliation occurred in 1982 but did not produce significant differences in light, temperature or macroalgal cover from 1979 and 1980. The results indicate that light and temperature can be limiting during the summer in spring-fed, headwater streams and that seed populations of some species are present in undetect-able levels during these periods of suboptimal growth conditions. In addition, it appears that stream macroalgal communities can be quite resilient, recovering rapidly following a major perturbation .     

Channels formed by colicin E1 in planar lipid bilayers are large and exhibit pH-dependent ion selectivity

Summary The E1 subgroup (E1, A, Ib, etc.) of antibacterial toxins called colicins are known to form voltage-dependent channels in planar lipid bilayers. The genes for colicins E1, A and Ib have been cloned and sequenced, making these channels interesting models for the widespread phenomenon of voltage dependence in cellular channels. In this paper we investigate ion selectivity and channel size—properties relevant to model building. Our major finding is that the colicin E1 channel is large, having a diameter ofat least 8 Å at its narrowest point. We established this from measurements of reversal potentials for gradients formed by salts of large cations or large anions. In so doing, we exploited the fact that the colicin channel is permeable to both cations and anions, and its relative selectivity to them is a functions and anions, and its relative selectivity to them is a function of pH. The channel is anion selective (Cl^– over K⁺) in neutral membranes, and the degree of selectivity is highly dependent on pH. In negatively charged membranes, it becomes cation selective at pH's higher than about 5. Experiments with pH gradients cross the membrane suggest that titratable groups both within the channel lumen and near the channel ends affect the selectivity. Individual E1 channels have more than one open conductance state, all displaying comparable ion selectivity. Colicins A and Ib also exhibit pH-dependent ion selectivity, and appear to have even larger lumens than E1.     

Induction of functional Fc receptors in P388 leukemia cells : Requirement for multiple differentiation signals

The development of functional Fc receptors (FcR) during induced differentiation with the tumor promoter, phorbol myristate acetate (PMA), was studied in the murine tumor cell line, P388. PMA induced the appearance of FcR on the membranes of P388 cells as indicated by the binding of IgG-coated sheep red blood cells (IgG-SRBC). Concentrations of PMA as low as 1 ng/ml were sufficient to induce the expression of FcR as well as to inhibit cellular division and to induce adherence in the P388 tumor cell line; however, optimal FcR induction occurred at PMA concentrations of 10-100 ng/ml. Immunofluorescent analysis with heat-aggregated myeloma proteins indicated that PMA induced FcR which were capable of binding IgG2a and IgG2b immunoglobulins, but not IgG1. Adherence to a substratum was determined to be a second required signal for expression of FcR, since PMA induction of P388 tumor cells in teflon dishes failed to fully develop FcR and adherence of P388 cells to poly-L-lysine-coated culture dishes in the absence of PMA was insufficient for FcR expression. FcR which appeared after PMA induction were non-functional in the sense that membrane-bound IgG-SRBC were not ingested to any significant extent by the tumor cells. However, if FcR induction occurred in the presence conA-induced rat spleen cell culture supernatants, phagocytosis of membrane-bound erythrocytes occurred. These findings suggest that for the expression of FcR which are capable of particle internalization, at least three identifiable membrane-transmitted signals are required during differentiation.     

Heparin binding to lipoprotein lipase and low density lipoproteins

Heparin was fractionated on an affinity column of bovine milk lipoprotein lipase (LpL) immobilized to Affi-Gel-15. The bound heparin, designated high-reactive heparin (HRH), enhanced LpL activity, presumably by stabilizing the enzyme against denaturation. The unbound heparin fraction had no observable effect on the initial rate of enzyme activity. However, at longer times of incubation there was inhibition of LpL activity. LpL-specific HRH also showed a high, Ca²⁺-dependent precipitating activity towards human plasma low density lipoproteins (LDL). Since LpL and LDL both bind to heparin-like molecules at the surface of the arterial wall, we suggest that their similar heparin-binding specificity may have physiological consequences as it relates to the development of atherosclerosis.

Heparin binding Lipoprotein lipase LDL Apolipoprotein Lipolysis     

Stable Equilibria at Two Loci in Populations with Large Selfing Rates

The equilibrium structure of two-locus, two-allele models with very large selfing rates is found using perturbation techniques. For free recombination, r = 1/2, the following results hold. If the heterozygotes do not have at least an approximate 30% advantage in fitness relative to homozygotes, a stable equilibrium with all alleles present is possible only if all of the homozygote fitnesses differ at most by approximately the outcrossing rate, t, and all stable polymorphic equilibria have disequilibrium values, D, that are at most on the order of the outcrossing rate. Once the heterozygote fitnesses are above the threshold, there are stable equilibria possible with D near its maximum possible value. The results show that the observed disequilibria in highly selfed plant populations are not likely to result from selection leading to an equilibrium.     

The Molecular through Ecological Genetics of Abnormal Abdomen in DROSOPHILA MERCATORUM. I. Basic Genetics

The abnormal abdomen syndrome (aa) in Drosophila mercatorum is characterized by the persistence of juvenilized cuticle on the adult abdomen. The aa phenotype is shown to depend on at least two X-linked genetic elements that are about one map unit apart near the centromeric end of the X chromosome. These two genetic elements are necessary for aa expression; one behaves as a dominant element and the other as a recessive. Overlaying these genetic studies upon molecular work reported elsewhere, it is argued that the dominant element is the presence of a 5 kb insertion in a majority of the X-linked repeats coding for the 28S ribosomal RNA. The recessive element appears to be a locus controlling differential replication of noninserted over inserted 28S genes during polytenization. The aa syndrome requires both the presence of the inserted repeats and the failure to preferentially amplify noninserted repeats. Given the necessary X-linked elements for aa, a variety of modifiers are revealed. First, aa expression in males is Y-linked, apparently corresponding to a deletion of the 18S/28S rDNA gene cluster normally found on the Y. Moreover, all major autosomes can modify the penetrance of aa.