Antimicrobial and antiviral activities of an actinomycete (Streptomyces sp.) isolated from a Brazilian tropical forest soil

A promising producer of bioactive compounds isolated from a Brazilian tropical soil was tested for its range of antimicrobial activities. Strain 606, classified as Streptomyces sp., could not be identified up to species level, suggesting a possible new taxon. The supernatant and 10 extracts and fractions, obtained by extraction and chromatographic techniques, presented antimicrobial activity using antibiograms. The methanolic fraction was highly active against pathogenic bacteria, phytopathogenic fungi and the human pathogenic yeast Candida albicans. It also possessed high antiviral activity inhibiting the propagation of an acyclovir-resistant herpes simplex virus type 1 strain on HEp-2 cells at non-cytotoxic concentration. The strong cytotoxic effect suggests an antitumour action. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of crude and affinity purified cytosolic epoxide hydrolases from hepatic tissue of control and clofibrate-fed mice

An affinity purification procedure was developed for the cytosolic epoxide hydrolase based upon the selective binding of the enzyme to immobilized methoxycitronellyl thiol. Several elution systems were examined, but the most successful system employed selective elution with a chalcone oxide. This affinity system allowed the purification of the cytosolic epoxide hydrolase activity from livers of both control and clofibrate-fed mice. A variety of biochemical techniques including pH dependence, substrate preference, kinetics, inhibition, amino acid analysis, peptide mapping, Western blotting, analytical isoelectric focusing, and gel permeation chromatography failed to distinguish between the enzymes purified from control and clofibrate-fed animals. The quantitative removal of the cytosolic epoxide hydrolase acting on trans-stilbene oxide from 100,000g supernatants, allowed analysis of remaining activities acting differentially on cis-stilbene oxide and benzo[a]pyrene 4,5-oxide. Such analysis indicated the existence of a novel epoxide hydrolase activity in the cytosol of mouse liver preparations.     

The Fine Structure of Some Retinal Photoreceptors

An electron microscope study has been made of octopus and amphibian photoreceptors, after fixing with KMnO₄ and embedding in araldite. What has previously been seen as a single dense stratum bounding the tubular compartments (octopus) or the double membrane discs (rods and cones), now shows a double structure. We interpret this as showing that these tubules and discs have similar bounding surfaces, which are probably directly related to the cell membrane. This is confirmed by the finding that the tubules and discs are (at least occasionally) continuous with the cell membrane.     

A nonselective cation channel activated by membrane deformation in oocytes of the ascidianBoltenia villosa

Summary Cell-attached patch clamp recordings from unfertilized oocytes of the ascidianBoltenia villosa reveal an ion channel which is activated by mechanical deformation of the membrane. These channels are seen when suction is applied to the patch pipette, but not in the absence of suction or during voltage steps. The estimated density of these stretch-activated channels is about 1.5/m², a figure equal to or greater than the density of known voltage-dependent channels in the oocyte. Ion substitution experiments done with combined whole-cell and attached patch recording, so absolute potentials are known, indicate that the channel passes Na⁺, Ca²⁺ and K⁺, but not Cl^–. The channel has at least two open and two closed states, with the rate constant that leaves the longer-lived closed state being the primary site of stretch sensitivity. External Ca²⁺ concentration affects channel kinetics: at low calcium levels, long openings predominate, whereas at high calcium virtually all openings are to the short-lived open state. In multiple channel patches, the response to a step change in suction is highly phasic, with channel open probability decreasing over several hundred milliseconds to a nonzero steady-state level after an initial rapid increase. This channel may play a role in the physiological response of cells of the early embryo to the membrane strains associated with morphogenetic events.     

Nesidioblastosis associated with hyperglycemia in two squirrel monkeys (Saimiri sciureus)

Abstract: Nesidioblastosis associated with progressive weight loss and hyperglycemia was diagnosed in two mid-adult, wild-caught, male squirrel monkeys (Saimiri sciureus). Hyperglycemia, glucosuria, and abnormal glucose tolerance test results were found when the monkeys were presented for clinical evaluation for chronic weight loss, episodic dehydration, hypothermia, and lethargy. Immunohistochemical studies of the pancreatic tissue demonstrated that the proliferating endocrine cells stained predominantly glucagon-positive in the most severely affected monkey.     

Genetic Variation and Random Drift in Autotetraploid Populations

The rate of decay of genetic variation is determined for randomly mating autotetraploid populations of finite size, and the equilibrium homozygosity under mutation and random drift is calculated. It is shown that heterozygosity is lost at a slower rate than in diploid populations, and that the equilibrium heterozygosity with mutation and random drift is higher than for diploids. Outcrossing populations as well as populations that randomly self are analyzed. A method of comparing genetic variation between autotetraploid and diploid populations is proposed. Our treatment suggests that the ``gametic homozygosity' provides a unified approach for comparing genotypes within a population as well as comparing genetic variation between populations with different levels of ploidy.     

A novel and high-throughput approach to assess photosynthetic thermal tolerance of kelp using chlorophyll α fluorometry

Foundation seaweed species are experiencing widespread declines and localized extinctions due to increased instability of sea surface temperature. Characterizing temperature thresholds are useful for predicting patterns of change and identifying species most vulnerable to extremes. Existing methods for characterizing seaweed thermal tolerance produce diverse metrics and are often time-consuming, making comparisons between species and techniques difficult, hindering insight into global patterns of change. Using three kelp species, we adapted a high-throughput method – previously used in terrestrial plant thermal biology – for use on kelps. This method employs temperature-dependent fluorescence (T–F₀) curves under heating or cooling regimes to determine the critical temperature (T_crit) of photosystem II (PSII), i.e., the breakpoint between slow and fast rise fluorescence response to changing temperature, enabling rapid assays of photosynthetic thermal tolerance using a standardized metric. This method enables characterization of T_crit for up to 48 samples per two-hour assay, demonstrating the capacity of T–F₀ curves for high-throughput assays of thermal tolerance. Temperature-dependent fluorescence curves and their derived metric, T_crit, may offer a timely and powerful new method for the field of phycology, enabling characterization and comparison of photosynthetic thermal tolerance of seaweeds across many populations, species, and biomes.     

Recolonization of estuarine organisms: effects of microcosm size and pesticides

Two six-week laboratory experiments were conducted to evaluate effects of pesticides and microcosm size on benthic estuarine macroinvertebrate recolonization. Sediments fortified with the pesticides (fenvalerate: controls, 5 (low) and 50 μg g⁻¹ wet sediment (high); endosulfan: controls, 1 (low) and 10 μg g⁻¹ wet sediment (high)) were fine-grained, organically rich (approximately 3.5% organic carbon and 22% dry weight) material. Relative dominance of the four most abundant taxa in both experiments was consistent among treatments with few exceptions. The amphipod,Corophium acherusicum, dominated abundance in both experiments. In the fenvalerate experiment, large trays (400 cm²) contained significantly (p<0.05) more total number of taxa (TNT) than small microcosms (144 cm²) but tray size was not significantly related to total number of organisms (TNO). When size was adjusted to a common unit area, small trays contained significantly more TNO than large containers. Adjusted abundance of small trays was 2.5 times that of large containers; a ratio close to that of microcosm sizes (i.e., 2.8). This result suggests that larval supply may have been inadequate to ‘aturate’ the available sediment in large containers. Fenvalerate significantly reduced abundance in the high treatment compared to both controls and low treatment but low treatment was not significantly different from controls. The amphipod,Corophium acherusicum, accounted for most of the decrease in abundance in response to fenvalerate. The holothruroid,Leptosynpta sp. and the polychaete,Mediomastus ambiseta, increased in abundance significantly with increased concentration of fenvalerate. Combined effects of actual microcosm size and concentration of endosulfan were not significant for TNO or TNT. As in the fenvalerate experiment, adjusted abundance of small microcosms was 2.6 times that of large trays which approximated the ratio of unit area between microcosm sizes. Abundance of a few taxa responded significantly to adjusted and unadjusted unit area. Abundance of the tunicate,Molgula manhattensis, increased significantly with increased concentration of endosulfan. Abundance was affected by sample location (e.g., interiorvs exterior cores) within microcosms. Abundance adjusted to unit area resulted in significantly greater TNO in externalvs internal cores. This has importance for sequential sub-sampling of microcosms to determine temporal dynamics. Statistically significant effects were measured in benthic community structure associated with microcosm size; however, the magnitude was relatively small. There appears to be no major biological reason to select one microcosm size over the other for screening for contaminant effects. Where feasible, the small trays provide savings in sample preparation and analysis, allow more replicates where laboratory space is limiting and generate less chemical waste. These benefits may be off-set by less ‘artifacts’ associated with edge effects of larger microcosms and the need for a larger mass of sediment to accommodate additional analytical requirements (e.g., thin vertical surficial samples to refine contaminant exposure at the sediment/water interface).     

Siderophore utilization and iron uptake by Rhodopseudomonas sphaeroides

The growth of Rhodopseudomonas sphaeroides in iron-deficient medium did not result in the production of detectable levels of siderophores of either the catechol or hydroxamate type. Iron-limited cultures of R. sphaeroides were not able to remove iron from ferric transferrin unless supplemented with 2,3-dihydroxybenzoic acid. R. sphaeroides was shown to take up 59Fe+3 when it was supplied as ferric chloride, ferric citrate, or ferric parabactin, but not when supplied as ferric rhodotorulate or ferric Desferal. When iron was supplied as ferric citrate, citrate was not taken up by the cells. The growth rate of R. sphaeroides under iron-limiting conditions was decreased by the addition of either Desferal or rhodotorulic acid, while the addition of citrate or parabactin did not affect growth.