EFFECTS OF THE PHYSICAL ENVIRONMENT ON SOME LIPOPROTEIN LAYER SYSTEMS AND OBSERVATIONS ON THEIR MORPHOGENESIS

Lipoprotein membrane systems such as chloroplasts and the endoplasmic reticulum exhibit a generalized swelling response. The initial effect is an increase in interlamellar spacing, but as swelling proceeds, the membranes are transformed into closed thin-walled spherical vesicles. Available evidence suggests that morphogenesis of the endoplasmic reticulum of Nitella and the lamellar system of the Zea chloroplasts involves fusion of small spherical vesicles to yield closed double membrane structures, which subsequently undergo further differentiation. It is suggested that the vesicles comprise a convenient "micellar" form by which lipides may be transported within the cell from the sites of lipide synthesis to regions of lamellar growth. The characteristic formation of vesicles in swelling and the apparent fusion of vesicles in morphogenesis appear to represent two aspects of a fundamental plasticity of lipoprotein layer systems.     

The hmu locus of Yersinia pestis is essential for utilization of free haemin and haem-protein complexes as iron sources

Yersinia pestis strains utilize haem and several haem-protein complexes as sole sources of iron. In this study, the haemin uptake locus (hmu) of Y. pestis KIM6+ was selected from a genomic library by trans-duction into an Escherichia coli siderophore synthesis (entC) mutant. Recombinant plasmids containing a common 16 kb BamHI insert were isolated that allowed E. coli entC to use haemin as an iron source. An 8.6 kb region of this insert was found to be essential for haemin utilization and encoded at least five proteins with molecular masses of 79/77, 44, 37, 35, and 30/27.5 kDa. A 10.9 kb Clal fragment containing the hmu locus showed varying degrees of homology to genomic DNA from Yersinia pseudotuberculosis, Yersinia enter-ocolitica, and other genera of Enterobacteriaceae. An E. coli hemA aroB strain harbouring cloned hmu genes used haemin as both an iron and porphyrin source but only on iron-poor medium, suggesting that haemin uptake is tightly iron regulated. Additionally, haemoglobin and myoglobin were used as iron sources by an E. coli entC (pHMU2.2) strain. Deletion of the hmu locus from Y. pestis KIM6+ chromosome generated a mutant that grew poorly on iron-depleted medium containing free haemin as well as mammalian haem-protein complexes including haemoglobin, haemoglobin-haptoglobin, myoglobin, haem-haemopexin, and haem-albumin unless it was complemented with cloned hmu genes.     

Site-directed mutagenesis of the katG gene of Mycobacterium tuberculosis: effects on catalase–peroxidase activities and isoniazid resistance

Recent studies examining the molecular mechanisms of isoniazid (INH) resistance in Mycobacterium tuberculosis have demonstrated that a significant percentage of drug-resistant strains are mutated in the katG gene which encodes a catalase–peroxidase, and the majority of these alterations are missense mutations which result in the substitution of a single amino acid. In previous reports, residues which may be critical for enzymatic activity and the drug-resistant phenotype have been identified by evaluating INH-resistant clinical isolates and in vitro mutants. In this study, site-directed mutagenesis techniques were utilized to alter the wild-type katG gene from M. tuberculosis at 13 of these codons. The effects of these mutations were determined using complementation assays in katG -defective, INH-resistant strains of Mycobacterium smegmatis and Mycobacterium bovis BCG. This mutational analysis revealed that point mutations in the katG gene at nine of the 13 codons can cause drug resistance, and that enzymatic activity and resistance to INH are inversely related. In addition, mutations in the mycobacterial catalase–peroxidase which reduce catalase activity also decrease peroxidase activity.     

Suckling behaviour in the brown long-eared bat (Plecotus auritus)

Thirty-two adult female brown long-eard bats were taken into captivity. Eight individuals gave birth to single young in captivity (known mother-young pairs), 10 were lactating when captured (putative mother-young pairs), and the remaining 14 bats were non-reproductive. Bats were maintained in five groups consisting of females from sigle(n=3) or mixed (n=2) wild roosts. All bats were housed in outdoor, free-flight enclosures and fed mainly on free-flying noctuid moths. Bats were individually were determined daily (n=152) for a single gruup of bats containing four known mother-young pairs and five non-reproductive bats. The probability of a being attached to the nipple declined from 100% of records at 1-5 days of age to 5% of records at 36-40 days of age. Females were always found suckling their own young. Suckling associations were determined using infra-red sensitive video-recordings of bat behaviour within the roost box. For both known (n=8) and putative mother-young pairs (n=10), there were no records of young attached to lactating females other than their own mothers (from the same or different wild roosts).     

Possible interference of fertilization in the natural recovery of a declining sugar maple stand in southern Quebec

A five year study was conducted in a 100–120 year old even-aged sugar maple stand in southern Quebec (46°07N 73° 56W; 305 m altitude) to explore the effect of different fertilization formulations aimed at 1) correcting the most common nutrient deficiencies observed in declining maple stands (K and Mg), 2) decreasing soil acidity, and 3) simulating enrichment with atmospheric N. Seven fertilizer mixtures were applied in the spring of 1987: 400 kg ha^-1 of K₂SO₄, CaCO₃, CaMg(CO₃)₂, (NH₄)₂SO₄, complete fertilizer (Maplegro) and 800 kg ha^-1 of an equal mixture of K₂SO₄+CaCO₃ or K₂SO₄+CaMg(CO₃)₂. The site was divided into twenty-four 25×25 m plots and treatments including control were replicated three times. Leaves and soils (organic and mineral) were sampled in 1987, 1988 and 1991. Trees were cored at 1.2 m to measure their response in diameter growth. The application of K₂SO₄+CaMg(CO₃)₂ was the only treatment that significantly increased (+13%) the average growth rate over the five year period after fertilization. The application of (NH₄)₂SO₄, Maplegro, CaMg(CO₃)₂ and K₂SO₄ reduced growth relative to the control for the five year period by 29, 24, 20 and 12 %, respectively. Positive and negative effects on growth can be explained mainly in terms of changes in leaf K. Both the application of Maplegro and (NH₄)₂SO₄ increased soil P availability. Overall, the rate of growth showed a cubic pattern of change over the 5 year period with peaks in 1988 and 1991. Trees in control plots went from a limiting foliar status of Ca and Mg, and surplus N in 1987 to a surplus of Ca and Mg, and lower N concentration in 1991. Our results suggest that nutrient deficiencies observed at our site were associated with a disturbance of the biogeochemical cycle of nutrients rather than soil nutrient depletion.Abbreviations BS base saturation - CEC cation exchange capacity - DRIS diagnosis and recommendation integrated system     

Formation of nesquehonite and other minerals as a consequence of biofilm dehydration

A microbial biofilm community was established over 971 days within gravel in an aquarium so as to model biofouling of an aquifer. When the water was allowed to evaporate slowly, white crystalline deposits, containing several carbonate and sulphate minerals including nesquehonite (MgCO₃.3H2O), were seen at the highest points on the surface of the biofouled gravel. No such deposits occurred in regions lacking biofilms. These crystals appeared to originate from evaporation of dissolved salts which had migrated through the biofilm. Surfaceadherent microbial biofilms may conceivably provide a conduit for solute transport in porous media such as soils and aquifers.     

Protein Phosphorylation and Calcium Uptake into Rat Forebrain Synaptosomes: Modulation by the σ Ligand, 1,3-Ditolylguanidine

Abstract: The σ ligand 1,3-di- O -tolylguanidine (DTG) increased basal dynamin and decreased depolarization-stimulated phosphorylation of the synaptosomal protein synapsin Ib without having direct effects on protein kinases or protein phosphatases. DTG dose-dependently decreased the basal cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) and blocked the depolarization-dependent increases in [Ca²⁺]_i. These effects were inhibited by the σ antagonists rimcazole and BMY14802. The nitric oxide donors sodium nitroprusside (SNP) and 8-( p -chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate decreased basal [Ca²⁺]_i and the KCl-evoked rise in [Ca²⁺]_i to an extent similar to DTG. SNP, but not DTG, produced a rise in cyclic GMP levels, suggesting that the effect of DTG on [Ca²⁺]_i was not mediated via downstream regulation of cyclic GMP levels. DTG increased ⁴⁵Ca²⁺ uptake and efflux under basal conditions and inhibited the ⁴⁵Ca²⁺ uptake induced by depolarization with KCl. The KCl-evoked rise in [Ca²⁺]_i was inhibited by ω-conotoxin (ω-CgTx)-GVIA and -MVIIC but not nifedipine and ω-agatoxin-IVA. The effect of DTG on decreasing the KCl-evoked rise in [Ca²⁺]_i was additive with ω-CgTx-MVIIC but not with ω-CgTx-GVIA. These data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca²⁺ levels via inhibition of N-type Ca²⁺ channels.     

Alterations in Glutamate Transporter Protein Levels in Kindling-Induced Epilepsy

Abstract: There is increasing evidence that levels of glutamate are elevated in certain brain regions immediately prior to and during induction and propagation of seizures. Modulation of high-affinity glutamate uptake is a potential mechanism responsible for the elevated levels observed with seizures. To date, three distinct Na⁺-dependent glutamate transporters have been cloned from rat and rabbit: GLT-1, GLAST, and EAAC-1. We performed a series of experiments to determine whether levels of these transporters are altered in amygdala-kindled rats. Levels of GLT-1, GLAST, and EAAC-1 were examined in three brain regions (hippocampus, piriform cortex/amygdala, and limbic forebrain) by quantitative immunoblotting using subtype-specific antibodies. GLAST protein was down-regulated in the piriform cortex/amygdala region of kindled rats as early as 24 h after one stage 3 seizure and persisting through multiple stage 5 seizures. In contrast, kindling induced an increase in EAAC-1 levels in piriform cortex/amygdala and hippocampus once the animals had reached the stage 5 level. No changes in GLT-1 were observed in any region examined. Changes in transporter levels could contribute to the changes in glutamate levels seen with kindling.