Identification and molecular characterisation of a fibrinogen binding protein from <Emphasis Type="Italic">Streptococcus iniae</Emphasis>.

Background  

Binding of serum components by surface M-related proteins, encoded by the emm genes, in streptococci constitutes a major virulence factor in this important group of organisms. The present study demonstrates fibrinogen binding by S. iniae, a Lancefield non-typeable pathogen causing devastating fish losses in the aquaculture industry and an opportunistic pathogen of humans, and identifies the proteins involved and their encoding genes.     

Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster

Hitchhiking effects of advantageous mutations have been invoked to explain reduced polymorphism in regions of low crossing-over in Drosophila. Besides reducing DNA heterozygosity, hitchhiking effects should produce strong linkage disequilibrium and a frequency spectrum skewed toward an excess of rare polymorphisms (compared to the neutral expectation). We measured DNA polymorphism in a Zimbabwe population of D. melanogaster at three loci, yellow, achaete, and suppressor of forked, located in regions of reduced crossing-over. Similar to previously published surveys of these genomic regions in other populations, we observed low levels of nucleotide variability. However, the frequency spectrum was compatible with a neutral model, and there was abundant evidence for recombination in the history of the yellow and ac genes. Thus, some aspects of the data cannot be accounted for by a simple hitchhiking model. An alternative hypothesis, background selection, might be compatible with the observed patterns of linkage disequilibrium and the frequency spectrum. However, this model cannot account for the observed reduction in nucleotide heterozygosity. Thus, there is currently no satisfactory theoretical model for the data from the tip and base of the X chromosome in D. melanogaster.      

Effect of Abscisic Acid on Uptake and Metabolism of [H]Gibberellin A(1) and [H]Pseudogibberellin A(1) by Barley Half-seeds

Uptake and metabolism of 1,2-[³H]gibberellin A₁ ([³H]GA₁, I) and its 3-hydroxy epimer ([³H]pseudoGA₁, II) by barley (Hordeum vulgare L.) half-seeds were measured after 24 hours of incubation, in the presence or absence of abscisic acid in the media. Uptake of both compounds was enhanced by abscisic acid, and abscisic acid enhanced the extent of metabolism of [³H]GA₁. However, [³H]pseudoGA₁ was not metabolized, even in the presence of abscisic acid. The significance of the stereo-chemistry of the 3-hydroxyl position is discussed.     

Tempo and mode of concerted evolution in the L1 repeat family of mice

A 300-bp DNA sequence has been determined for 30 (10 from each of three species of mice) random isolates of a subset of the long interspersed repeat family L1. From these data we conclude that members of the L1 family are evolving in concert at the DNA sequence level in Mus domesticus, Mus caroli, and Mus platythrix. The mechanism responsible for this phenomenon may be either duplicative transposition, gene conversion, or a combination of the two. The amount of intraspecies divergence averages 4.4%, although between species base substitutions accumulate at the rate of approximately 0.85%/Myr to a maximum divergence of 9.1% between M. platythrix and both M. domesticus and M. caroli. Parsimony analysis reveals that the M. platythrix L1 family has evolved into a distinct clade in the 10-12 Myr since M. platythrix last shared a common ancestor with M. domesticus and M. caroli. The parsimony tree also provides a means to derive the average half-life of L1 sequences in the genome. The rates of gain and loss of individual copies of L1 were estimated to be approximately equal, such that approximately one-half of them turn over every 3.3 Myr.      

Interactions between Bdellovibrio and its host cell.

The bdellovibrios are extremely small bacteria with the unique property of being parasites of other (gram-negative) bacteria. In the presence of viable and susceptible bacteria a Bdellovibrio cell physically 'attacks' an individual host cell, attaches to its surface, penetrates the cell wall, and multiples within the periplasmic (intramural) space of its prey. The invading Bdellovibrio and its progeny degrade and consume the cellular constituents of the invaded host bacterium. This process finally results in complete lysis of the host cell and release of the Bdellovibrio progeny. From a population of parasitic bdellovibrios, derivatives can be selected that grow on complex nutrient media. Currently, none of the different nutritional types can be propagated in a fully defined synthetic medium. By degradation of the cellular constituents of the host the Bdellovibrio cell in its periplasmic space has available all the monomeric subunits needed to synthesis of the macromolecules. Peculiarities of Bdellovibrio metabolism with respect to uptake of preformed molecules and energy efficiency are discussed.     

Polymorphism and divergence at the 5' flanking region of the sex- determining locus, Sry, in mice

We have investigated patterns of evolution in the nonrecombining portion of the Y chromosome in mice by comparing levels of polymorphism within Mus domesticus with levels of divergence between M. domesticus and M. spretus. A 1,277-bp fragment of noncoding sequence flanking the sex determining locus (Sry) was PCR amplified, and 1,063 bases were sequenced and compared among 20 M. domesticus and 1 M. spretus. Two polymorphic base substitutions and two polymorphic insertion/deletion sites were identified within M. domesticus; nucleotide diversity was estimated to be 0.1%. Divergence between M. domesticus and M. spretus for this region (1.9%) was slightly lower than the average divergence of single-copy nuclear DNA for these species. Comparison of levels of polymorphism and divergence at Sry with levels of polymorphism and divergence in the mitochondrial DNA control region provided no evidence of a departure from the expectations of neutral molecular evolution. These findings are consistent with the presumed lack of function for much of the Y chromosome.      

Regulation of prolactin secretion in canine pituitary-dependent hyperadrenocorticism

In 15 dogs with pituitary-dependent hyperadrenocorticism (PDH) the basal prolactin concentrations (means of 6 determinations; range 2.8-24.7 micrograms/l) were significantly higher than those of 23 healthy control dogs (0.9-10.5 micrograms/l). In five dogs with hyperadrenocorticism due to adrenocortical tumour (ATH) the prolactin concentrations were also significantly elevated, but still significantly lower than the values of the dogs with PDH. The prolactin concentrations of the dogs with PDH responded supranormally to TRH-stimulation, whereas in the dogs with ATH the response was not significantly different from the results in the control dogs. Following bromocriptine administration the plasma prolactin concentrations of the dogs with PDH decreased considerably but remained higher than the values obtained in the control dogs and the dogs with ATH. It is concluded that PDH in the dog is associated with a disturbance in the regulation of prolactin secretion, that is not secondary to hypercortisolism per se.     

Pulmonary gas exchange in humans exercising at sea level and simulated altitude

In a previous study of normal subjects exercising at sea level and simulated altitude, ventilation-perfusion (VA/Q) inequality and alveolar-end-capillary O2 diffusion limitation (DIFF) were found to increase on exercise at altitude, but at sea level the changes did not reach statistical significance. This paper reports additional measurements of VA/Q inequality and DIFF (at sea level and altitude) and also of pulmonary arterial pressure. This was to examine the hypothesis that VA/Q inequality is related to increased pulmonary arterial pressure. In a hypobaric chamber, eight normal subjects were exposed to barometric pressures of 752, 523, and 429 Torr (sea level, 10,000 ft, and 15,000 ft) in random order. At each altitude, inert and respiratory gas exchange and hemodynamic variables were studied at rest and during several levels of steady-state bicycle exercise. Multiple inert gas data from the previous and current studies were combined (after demonstrating no statistical difference between them) and showed increasing VA/Q inequality with sea level exercise (P = 0.02). Breathing 100% O2 did not reverse this increase. When O2 consumption exceeded about 2.7 1/min, evidence for DIFF at sea level was present (P = 0.01). VA/Q inequality and DIFF increased with exercise at altitude as found previously and was reversed by 100% O2 breathing. Indexes of VA/Q dispersion correlated well with mean pulmonary arterial pressure and also with minute ventilation. This study confirms the development of both VA/Q mismatch and DIFF in normal subjects during heavy exercise at sea level. However, the mechanism of increased VA/Q mismatch on exercise remains unclear due to the correlation with both ventilatory and circulatory variables and will require further study.     

A scaffoldless technique for self-generation of three-dimensional keratinospheroids on liquid crystal surfaces

We describe a new scaffold-free three-dimensional (3D) cell culture model using cholesteryl ester based lyotropic liquid crystal (LC) substrates. Keratinocytes were deposited randomly on the LC surface where they self-assembled into 3D microtissues or keratinospheroids. The cell density required to form spheroids was optimized. We investigated cell viability using dead/live cell assays. The adhesion characteristics of cells within the microtissues were determined using histological sectioning and immunofluorescence staining. Fourier transform infrared spectroscopy (FTIR) was used to characterize the biochemistry of the keratinospheroids. We found that both cells and microtissues could migrate on the LC surface. The viability study indicated approximately 80% viability of cells in the microtissues up to 20 days of culture. Strong intercellular adhesion was observed in the stratification of the multi-layered microspheroids using field emission-scanning electron microscopy (FE-SEM) and histochemical staining. The cytoskeleton and vinculins of the cells in the microtissues were expressed diffusely, but the microtissues were enriched with lipids and nucleic acids, which indicates close resemblance to the conditions in vivo. The basic 3D culture model based on LC may be used for cell and microtissue migration studies in response to cytochemical treatment.     

Influence of soil water potential on respiration and nitrogen fixation ofAzotobacter vinelandii

Summary Respiration and N₂-fixation (acetylene reduction) ofAzotobacter vinelandii have been studied at a variety of soil water potentials. Both processes were strictly linked and strongly reduced at water potentials between –0.6 and –1.3 MPa. Complete inhibition occurred below –2.1MPa. Osmotic potentials in soil compared to matric potentials of the same value were less inhibitory to respiration and acetylene reduction by Azotobacter. The N₂-fixing efficiency (mg N/g glucose) was not influenced by water potentials ranging from –0.1 to –2.1 MPa.