Development and application of the active surveillance of pathogens microarray to monitor bacterial gene flux

Background  

Human and animal health is constantly under threat by emerging pathogens that have recently acquired genetic determinants that enhance their survival, transmissibility and virulence. We describe the construction and development of an Active Surveillance of Pathogens (ASP) oligonucleotide microarray, designed to 'actively survey' the genome of a given bacterial pathogen for virulence-associated genes.     

Thermal plasticity in Drosophila melanogaster : A comparison of geographic populations

Background  

Populations of Drosophila melanogaster show differences in many morphometrical traits according to their geographic origin. Despite the widespread occurrence of these differences in more than one Drosophila species, the actual selective mechanisms controlling the genetic basis of such variation are not fully understood. Thermal selection is considered to be the most likely cause explaining these differences.     

Oxygen radicals in ulcerative colitis.

This article reviews the pathophysiologic concept that superoxide and hydrogen peroxide, generated by activated leukocytes, together with low-molecular-weight chelate iron derived from fecal sources and from denatured hemoglobin, amplify the inflammatory response and subsequent mucosal damage in patients with active episodes of ulcerative colitis. The putative pathogenic mechanisms reviewed are as follows: (1) Dietary iron is concentrated in fecal material owing to normally limited iron absorption. (2) Mucosal bleeding, characteristic of ulcerative colitis, as well as supplemental oral iron therapy for chronic anemia, further conspire to maintain or elevate mucosal iron concentration in colitis. (3) Fenton chemistry, driven especially by leukocyte-generated superoxide and hydrogen peroxide, leads to formation of hydroxyl radicals. (4) The resultant oxidative stress leads to the extension and propagation of crypt abscesses, either through direct membrane disruption by lipid peroxidation or through generation of secondary toxic oxidants such as chloramines. (5) Chemotactic products of lipid peroxidation, including 4-hydroxynonenal, provide positive feedback to accelerate this inflammatory/oxidative process, leading to acute exacerbations of the disease. (6) Other oxidized products, such as oxidized tryptophan metabolites, created by free radical mechanisms in or near the mucosa, may act as carcinogens or tumor promotors that contribute to the exceedingly high incidence of colon carcinoma in patients suffering from chronic ulcerative colitis. In this way, self-sustaining cycles of oxidant formation may amplify flare-ups of inflammation and mucosal injury in ulcerative colitis. This concept, if proved correct by subsequent research, would provide a rationale for several novel clinical approaches to the management of ulcerative colitis, including use of SOD mimetics, iron chelators, and chain-breaking antioxidants.     

Mechanical Properties of Calvarial Bones in a Mouse Model for Craniosynostosis

The mammalian cranial vault largely consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Premature closure of the cranial sutures, craniosynostosis, can lead to serious clinical pathology unless there is surgical intervention. Research into the genetic basis of the disease has led to the development of various animal models that display this condition, e.g. mutant type Fgfr2^C342Y/+ mice which display early fusion of the coronal suture (joining the parietal and frontal bones). However, whether the biomechanical properties of the mutant and wild type bones are affected has not been investigated before. Therefore, nanoindentation was used to compare the elastic modulus of cranial bone and sutures in wild type (WT) and Fgfr2^C342Y/+mutant type (MT) mice during their postnatal development. Further, the variations in properties with indentation position and plane were assessed. No difference was observed in the elastic modulus of parietal bone between the WT and MT mice at postnatal (P) day 10 and 20. However, the modulus of frontal bone in the MT group was lower than the WT group at both P10 (1.39±0.30 vs. 5.32±0.68 GPa; p<0.05) and P20 (5.57±0.33 vs. 7.14±0.79 GPa; p<0.05). A wide range of values was measured along the coronal sutures for both the WT and MT samples, with no significant difference between the two groups. Findings of this study suggest that the inherent mechanical properties of the frontal bone in the mutant mice were different to the wild type mice from the same genetic background. These differences may reflect variations in the degree of biomechanical adaptation during skull growth, which could have implications for the surgical management of craniosynostosis patients.     

Evolutionary divergence times in the Annonaceae: evidence of a late Miocene origin of Pseuduvaria in Sundaland with subsequent diversification in New Guinea

Background  

Phylogenetic analyses of the Annonaceae consistently identify four clades: a basal clade consisting of Anaxagorea, and a small 'ambavioid' clade that is sister to two main clades, the 'long branch clade' (LBC) and 'short branch clade' (SBC). Divergence times in the family have previously been estimated using non-parametric rate smoothing (NPRS) and penalized likelihood (PL). Here we use an uncorrelated lognormal (UCLD) relaxed molecular clock in BEAST to estimate diversification times of the main clades within the family with a focus on the Asian genus Pseuduvaria within the SBC. Two fossil calibration points are applied, including the first use of the recently discovered Annonaceae fossil Futabanthus. The taxonomy and morphology of Pseuduvaria have been well documented, although no previous dating or biogeographical studies have been undertaken. Ancestral areas at internal nodes within Pseuduvaria are determined using dispersal-vicariance analysis (DIVA) and weighted ancestral area analysis (WAAA).     

New genes of Xanthomonas citri subsp. citri involved in pathogenesis and adaptation revealed by a transposon-based mutant library

Background  

Citrus canker is a disease caused by the phytopathogens Xanthomonas citri subsp. citri, Xanthomonas fuscans subsp. aurantifolli and Xanthomonas alfalfae subsp. citrumelonis. The first of the three species, which causes citrus bacterial canker type A, is the most widely spread and severe, attacking all citrus species. In Brazil, this species is the most important, being found in practically all areas where citrus canker has been detected. Like most phytobacterioses, there is no efficient way to control citrus canker. Considering the importance of the disease worldwide, investigation is needed to accurately detect which genes are related to the pathogen-host adaptation process and which are associated with pathogenesis.     

Lethal hydroxyl radical production in paraquat-treated plants

Bipyridinium herbicides, including paraquat and diquat, are believed to act by generating highly reactive, oxygen-centered free radicals within chloroplasts when treated plants are exposed to sunlight. This hypothesis has not yet been confirmed by direct chemical measurements of specific free radicals. We studied paraquat-treated plants using a new method able to detect and quantify formation of highly reactive and deleterious hydroxyl radicals (HO^*), in which dimethyl sulfoxide (DMSO) is used as a molecular probe. DMSO is oxidized by HO^* to form the stable, nonradical compound, methane sulfinic acid, which can be easily extracted from plant tissue and measured spectrophotometrically. Initial experiments revealed formation of extraordinary numbers of hydroxyl radicals in light-exposed, paraquat + DMSO-treated plants, equivalent at least to the cumulative number of HO^* radicals per gram of fresh tissue that would be produced by 10,000 rads of gamma irradiation. This appears to be the greatest production of hydroxyl radicals yet observed in a biological system and is quite sufficient to explain the rapid death of top growth in paraquat-treated plants.     

Effect of oxygen concentration on the formation of molondialdehyde-like material in a model of tissue ischemia and reoxygenation

This study was conducted to explore the functional relationship between oxygen concentration during tissue reoxygenation after ischemia and the extent of postischemic lipid peroxidation, an indicator of reoxygenation injury. Excised rat liver or kidney tissue was rendered ischemic for 1 h at 37°C, minced into 1 mm³ fragments, and then reoxygenated for 1 h in flasks of buffered salt solution containing various amounts of oxygen. Production of malondialdehyde-like material (MDA) was measured to indicate lipid peroxidation. MDA production was minimal at oxygen tensions less than 10 mmHg, increased sharply from 10 to 50 mmHg, and plateaued at approximately 100 mmHg. A similar functional relationship was produced by a simple mathematical model of free radical mediated lipid peroxidation in biological membranes, suggesting that MDA production is indeed caudes by free radical oxidation of membrane phospholipids and that the oxygen effect is governed by simple competition between chain propagation and chain termination reactions within the membrane. These experimental and analytical results confirm that relatively low concentrations of oxygen are sufficient to produce oxidative damage in post-ischemic tissues.