Diversity in nucleotide acquisition by antigenically similar Chlamydia psittaci of avian origin

Abstract Two different nucleic acid precursor utilization patterns were obtained for five avian isolates of Chlamydia psittaci . Three of the isolates bahaved in a manner similar to that previously described, showing total dependency on the host cell for ribonucleoside triphosphates and being unable to utilize medium-supplied thymidine. In contrast, the other two isolates were incapable of taking pyrimidine ribonucleotides from the host cell and they could efficiently utilize medium-supplied thymidine. These unusual isolates were resistant to 5-fluorouridine while the other three isolates were sensitive. Of the five isolates only 6BC was sensitive to sulfonamides. The five isolates were divided into two groups by comparing the Alu I restriction endonuclease patterns obtained following digestion of the major outer membrane protein (OMP1) gene, amplified by the polymerase chain reaction. The OMP1 genotyping results were confirmed by serotyping.     

Improved pulse sequences for measuring coupling constants in 13C, 15N-labeled proteins

Summary NMR pulse sequences for measuring coupling constants in ¹³C, ¹⁵N-labeled proteins are presented. These pulse sequences represent improvements over earlier experiments with respect to resolution and number of radiofrequency pulses. The experiments are useful for measuring J_NH , J_NCO, J_NC , J_H ^N _CO and J_H ^N _H . Applications to chymotrypsin inhibitor 2 (CI-2) are shown.     

A NEW PHYLOGENY FOR CHROMOPHYTE ALGAE USING 16S-LIKE RRNA SEQUENCES FROM MALLOMONAS PAPILLOSA (SYNUROPHYCEAE) AND TRIBONEMA AEQUALE (XANTHOPHYCEAE)1

The 16S-like ribosomal RNA genes from Mallomonas papillosa Harris et Bradley (Synurophyceae) and Tribonema aequale Pascher (Xanthophyceae) were sequenced and compared to those of other eukaryotes. Mallomonas is closely related to Ochromonas (Chrysophyceae) and supports the general hypothesis of a close phylogenetic relationship between the Synurophyceae and Chrysophyceae. Tribonema is specifically related to Costaria costata (C. A. Agardh) Saunders (Phaeophyceae) demonstrating an unexpected phylogenetic relationship between the Xanthophyceae and Phaeophyceae. Distance and parsimony analysis place these four chromophyte genera in a complex evolutionary assemblage that includes the Bacillariophyceae and Oomycetes but excludes the Dinophyceae. The close relationship between the chromophyte algae and the Öomycete fungi supports the hypothesis that protists with tripartite hairs form a natural assemblage.     

Changes in the Visual Cell Layer of the Duplex Retina During Growth of the Eye of a Deep-sea Teleost,Gempylus serpens Cuvier, 1829

Ontogenetic changes in the visual cell layer of the duplex retina during growth of the eye of the deep-sea teleost Gempylus serpens, the snake mackerel, are illustrated by comparing the retina of a small specimen with that of a previously studied adult fish. The small specimen has tightly packed cones spanning the whole width of the visual cell layer and small rods situated in its vitread part. Over most of the retina the cone population consists of single cones arranged in a very regular hexagonal mosaic. The temporalmost retina has a cone population consisting mainly of twin cones arranged in meridional rows. Growth of the eye is associated with an increase in the thickness of the visual cell layer and the density of rods and a total elimination of the densely packed single cones, the retina of the adult fish possessing only a temporally located population of double cones. The radical differences between the retina of the small and adult snake mackerel are probably associated with the different light regimes encountered by small and large specimens.     

COMPETITION BETWEEN STAURASTRUM LUETKEMUELLERII (CHLOROPHYCEAE) AND MICROCYSTIS AERUGINOSA(CYANOPHYCEAE) UNDER VARYING MODES OF PHOSPHATE SUPPLY1

The desmid Staurastrum luetkemuellerii Donat et Ruttner and the cyanobacterium Microcystis aeruginosa Kütz. were grown in mixed cultures with various phosphate (P_i) additions. One pulse of P_i each day (semi-continuous cultures) favored M. aeruginosa whereas S. luetkemuellerii was favored when the same quantity of P_i was supplied continuously (chemostats). Both species coexisted under P limitation provided that the nutrient was supplied in an appropriate mode. The ability of each species to compete for P depended on their P_i uptake characteristics and their capability to retain the accumulated P_i. High affinity in uptake at low P_i concentrations contributed considerably to the growth eficiency of S. luetkemuellerii under continuous supply of P_iM. aeruginosa was, however, consistently superior to S. luetkemuellerii in accuniulatiug the newly added P, but had a high rate of P_i release. In both -types of cultures, a net high of P went from M. aeruginosa to S. luetkemuellerii. The kinetic characteristics of the two species were used to simulate the outcome of competition experiments. Simulations agreed with the experimental data f both uptake and P_i release were considered in the model. The zlariable P*(the concentration of P_i at which the net uptake is equal to μ·Q_P is a function of uptake and release of P_i but could not explain the chemostat results. S. luetkemuellerii was the winner in many experiments even if its P*was higher thou that of M. aeruginosa. Thus, in the present case P_c (the concentration at which the net uptake is zero) was a better predictor of the ability to compete for P_i under steady state as well as transient conditions in the P_i supply.     

A Sperm Midpiece Defect in a Hereford Bull with Variable Semen Quality and Freezability

A midpiece sperm defect with a frequency of 25-35% in ejaculates obtained from a Hereford bull with a 60 d non-retum rate of 76.4% after careful pre- and postfreeze semen selection was studied in light microscope and by transmission electron microscopy. The defect consisted in a folding and coiling of the distal midpiece characterized by disorganization and irregularity of mitochondria surrounding the axial fiber bundle, combined with retraction of doublet fibers and dislocation and fracturing of these elements and the corresponding dense fibers. Based on examination of the sper- matogenic epithelium it was concluded that the alterations in the axial fiber bundle were secondary to those in the mitochondrial sheath. The abnormality appeared to be related to the “Dag-like” defect earlier observed in different breeds.     

Double blind randomised controlled trial of effect of metoprolol on myocardial ischaemia during endoscopic cholangiopancreatography.

OBJECTIVE--To evaluate the effect of metoprolol, a beta adrenergic blocking drug, on the occurrence of myocardial ischaemia during endoscopic cholangiopancreatography. DESIGN--Double blind, randomised, controlled trial. SETTING--University Hospital. SUBJECTS--38 (two groups of 19) patients scheduled for endoscopic cholangiopancreatography. INTERVENTIONS--Metoprolol 100 mg or placebo as premedication two hours before endoscopy. MAIN OUTCOME MEASURES--Heart rate, arterial oxygen saturation by continuous pulse oximetry, ST segment changes during endoscopic cholangiopancreatography (an ST segment deviation > 1 mV was defined as myocardial ischaemia), electrocardiogram monitored continuously with a Holter tape recorder. RESULTS--All patients had increased heart rate during endoscopy compared with rate before endoscopy, but heart rate during endoscopy was significantly lower in the metoprolol group compared with the placebo group (P = 0.0002). Twenty one patients (16 placebo, 5 metoprolol; P = 0.0008) developed tachycardia (heart rate > 100/min) during the procedure, and 11 patients (10 placebo, 1 metoprolol; P = 0.003) developed myocardial ischaemia. One patient in the placebo group had an acute inferolateral myocardial infarction. In the 10 other patients with signs of myocardial ischaemia during endoscopy the ST deviation disappeared when the endoscope was retracted. In all patients myocardial ischaemia was related to increases in heart rate, and 10 of the 11 patients had tachycardia coherent with myocardial ischaemia. CONCLUSIONS--Metoprolol prevented myocardial ischaemia during endoscopic cholangiopancreatography, probably through lowering the heart rate. Thus, tachycardia seems to be a key pathogenic factor in the development of myocardial ischaemia during endoscopy.