Flanking and internal regions of chromosomal genes mediating aerobactin iron uptake systems in enteroinvasive Escherichia coli and Shigella flexneri

We have investigated the presence of the aerobactin system and the location of the aerobactin genes in enteroinvasive strains of Escherichia coli. Also, we cloned the aerobactin region and its flanking sequences from the chromosome of a strain of Shigella flexneri and compared the molecular organization of the aerobactin genes in the two genera. Of the 11 enteroinvasive E. coli strains studied, 5 possessed the aerobactin genes, which were located on the chromosome in each case. These strains produced and utilized aerobactin and also were susceptible to the bacteriocin cloacin-DF13. Restriction endonuclease mapping and hybridization experiments showed that the regions corresponding to the aerobactin-specific sequences were very similar in both enteroinvasive E. coli and S. flexneri. However, differences were found in the region corresponding to the aerobactin receptor gene. The regions flanking the aerobactin system in enteroinvasive E. coli and S. flexneri exhibited some similarities but were different from those in pColV-K30. Under iron-limiting conditions, aerobactin-producing enteroinvasive E. coli and S. flexneri synthesized outer-membrane proteins of 76 and 77 kDa, respectively, which cross-reacted immunologically with rabbit antiserum raised against the 74 kDa pColV-K30-encoded ferric aerobactin receptor.

Occurrence of chromosome- or plasmid-mediated aerobactin iron transport systems and hemolysin production among clonal groups of human invasive strains of Escherichia coli K1

The incidence of the aerobactin system and the genetic location of aerobactin genes were investigated in Escherichia coli K1 neonatal isolates belonging to different clonal groups. A functional aerobactin system was found in all members of the O7 MP3, O1 MP5, O1 MP9, and O18 MP9 clonal groups examined and also in K1 strains having O6, O16, and O75 lipopolysaccharide types, which are less frequently associated with neonatal infections. In contrast, the aerobactin system was not detected in strains from the O18 MP6 clone. The combined results of plasmid and colony hybridization experiments showed that the aerobactin genes were located on the chromosome in the majority (75%) of the aerobactin-producing K1 isolates, the genetic location of the aerobactin genes was closely correlated with the outer membrane protein profile rather than the O lipopolysaccharide type, the K1 strains harboring a chromosome-mediated aerobactin system did not possess colicin V genes, and five of six K1 isolates possessing a plasmid-borne aerobactin system contained colicin V genes which were located on the same plasmids carrying the aerobactin genes. The comparison of hemolysin production with possession of the aerobactin system in virulent clones of E. coli K1 strains showed that all of the aerobactin-producing strains from the O18 MP9 and O7 MP3 clonal groups did not synthesize hemolysin, whereas 11 of 12 aerobactin-nonproducing O18 MP6 isolates were hemolytic. Of the K1 strains examined, 92.5% possessed either the aerobactin system or the ability to produce hemolysin or both.

Aerobactin iron transport genes commonly encoded by certain ColV plasmids occur in the chromosome of a human invasive strain of Escherichia coli K1

The aerobactin-mediated iron uptake system encoded by pColV-K30 and other ColV plasmids has been associated with the ability of Escherichia coli strains to cause disease. We investigated whether the pColV-K30 aerobactin system is present in E. coli K1 VW187 isolated from a human neonate with meningitis. This strain exhibited a functional aerobactin-mediated iron uptake system, as assessed by a cross-feeding bioassay and by its sensitivity to cloacin, a bacteriocin that recognizes the outer membrane receptor for iron-aerobactin complexes. By using a variety of techniques, we could not find any plasmid harboring the aerobactin genes. Hybridization of restriction endonuclease-cleaved chromosomal DNA from strain VW187 with various clones containing subsets of the pColV-K30 aerobactin region showed that the aerobactin genes were located on a 10.5-kilobase-pair chromosomal HindIII restriction fragment which also contained IS1-like insertion sequences. The chromosomal aerobactin region showed a high degree of conservation when compared with the homologous region in plasmid pColV-K30, although it was located on a different restriction endonuclease site environment.

Iron Age Pastoral Nomadism and Agriculture in the Eastern Eurasian Steppe: Implications from Dental Palaeopathology and Stable Carbon and Nitrogen Isotopes

Iron Age societies of the eastern Eurasian steppe are traditionally viewed as nomadic pastoralists. However, recent archaeological and anthropological research in Kazakhstan has reminded us that pastoralist economies can be highly complex and involve agriculture. This paper explores the nature of the pastoralist economies in two Early Iron Age populations from the burial grounds of Ai-Dai and Aymyrlyg in Southern Siberia. These populations represent two cultural groups of the Scythian World - the Tagar Culture of the Minusinsk Basin and the Uyuk Culture of Tuva. Analysis of dental palaeopathology and carbon and nitrogen stable isotopes suggests that domesticated cereals, particularly millet, and fish formed a major component of the diet of both groups. The findings contribute to the emerging picture of the nuances of Early Iron Age subsistence strategies on the eastern steppe.

A test of the extended intergroup contact hypothesis: The mediating role of intergroup anxiety, perceived ingroup and outgroup norms, and inclusion of the outgroup in the self

S. C. Wright, A. Aron, T. McLaughlin-Volpe, and S. A. Ropp (1997) proposed that the benefits associated with cross-group friendship might also stem from vicarious experiences of friendship. Extended contact was proposed to reduce prejudice by reducing intergroup anxiety, by generating perceptions of positive ingroup and outgroup norms regarding the other group, and through inclusion of the outgroup in the self. This article documents the first test of Wright et al.'s model, which used structural equation modeling among two independent samples in the context of South Asian-White relations in the United Kingdom. Supporting the model, all four variables mediated the relationship between extended contact and outgroup attitude, controlling for the effect of direct contact. A number of alternative models were ruled out, indicating that the four mediators operate concurrently rather than predicting one another.

The renin-angiotensin system and antihypertensive drugs in Alzheimer's disease:current standing of the angiotensin hypothesis?

There is an urgent need to improve upon Alzheimer's disease (AD) treatments. Limitations of existing drugs are that they target specific downstream neurochemical abnormalities while the upstream underlying pathology continues unchecked. Preferable treatments would be those that can target a number of the broad range of molecular and cellular abnormalities that occur in AD such as amyloid-ß (Aß) and hyperphosphorylated tau-mediated damage, inflammation, and mitochondrial dysfunction, as well more systemic abnormalities such as brain atrophy, impaired cerebral blood flow (CBF), and cerebrovascular disease. Recent pre-clinical, epidemiological, and a limited number of clinical investigations have shown that prevention of the signaling of the multifunctional and potent vasoconstrictor angiotensin II (Ang II) may offer broad benefits in AD. In addition to helping to ameliorate co-morbid hypertension, these drugs also likely improve diminished CBF which is common in AD and can contribute to focal Aß pathology. These drugs, angiotensin converting enzyme (ACE) inhibitors, or angiotensin receptor antagonists (ARAs) may also help deteriorating cognitive function by preventing Ang II-mediated inhibition of acetylcholine release as well as interrupt the upregulation of deleterious inflammatory pathways that are widely recognized in AD. Given the current urgency to find better treatments for AD and the relatively immediate availability of drugs that are already widely prescribed for the treatment of hypertension, one of the largest modifiable risk factors for AD, this article reviews current knowledge as to the eligibility of ACE-inhibitors and ARAs for consideration in future clinical trials in AD.

Modeling colloid deposition on a protein layer adsorbed to iron-oxide-coated sand

Our recent study reported that conformation change of granule-associated Bovine Serum Albumin (BSA) may influence the role of the protein controlling colloid deposition in porous media (Flynn et al., 2012). The present study conceptualized the observed phenomena with an ellipsoid morphology model, describing BSA as an ellipsoid taking a side-on or end-on conformation on granular surface, and identified the following processes: (1) at low adsorbed concentrations, BSA exhibited a side-on conformation blocking colloid deposition; (2) at high adsorbed concentrations, BSA adapted to an end-on conformation promoted colloid deposition; and (3) colloid deposition on the BSA layer may progressively generate end-on molecules (sites) by conformation change of side-on BSA, resulting in sustained increasing deposition rates. Generally, the protein layer lowered colloid attenuation by the porous medium, suggesting the overall effect of BSA was inhibitory at the experimental time scale. A mathematical model was developed to interpret the ripening curves. Modeling analysis identified the site generation efficiency of colloid as a control on the ripening rate (declining rate in colloid concentrations), and this efficiency was higher for BSA adsorbed from a more dilute BSA solution. © 2012 Elsevier B.V.

Testing the Prebish-Singer hypothesis using second-generation panel data stationarity tests with a break

In this paper, we test the Prebish-Singer (PS) hypothesis, which states that real commodity prices decline in the long run, using two recent powerful panel data stationarity tests accounting for cross-sectional dependence and a structural break. We find that the hypothesis cannot be rejected for most commodities other than oil.

Arsenic rich iron plaque on macrophyte roots--an ecotoxicological risk?

Arsenic is known to accumulate with iron plaque on macrophyte roots. Three to four years after the Aznalcóllar mine spill (Spain), residual arsenic contamination left in seasonal wetland habitats has been identified in this form by scanning electron microscopy. Total digestion has determined arsenic concentrations in thoroughly washed 'root+plaque' material in excess of 1000 mg kg(-1), and further analysis using X-ray absorption spectroscopy suggests arsenic exists as both arsenate and arsenite. Certain herbivorous species feed on rhizomes and bulbs of macrophytes in a wide range of global environments, and the ecotoxicological impact of consuming arsenic rich iron plaque associated with such food items remains to be quantified. Here, greylag geese which feed on Scirpus maritimus rhizome and bulb material in areas affected by the Aznalcóllar spill are shown to have elevated levels of arsenic in their feces, which may originate from arsenic rich iron plaque.

Arsenic mobilization from iron oxyhydroxides is regulated by organic matter carbon to nitrogen (C:N) ratio

Arsenic (As) is mobilized from delta and floodplain aquifer sediments throughout S.E. Asia via reductive dissolution of As bound to iron (Fe) oxyhydroxides. The reductive driving force is organic carbon, but its source and constitution is uncertain. Here batch incubation experiments were conducted to investigate the role of organic matter (OM) carbon:nitrogen (C:N) ratio on the mobilization of arsenic, Fe and N from As dosed, Fe oxyhydroxide coated sands. As mobilization into pore waters from the sand was strongly regulated by the C:N ratio of the OM, and also the concentration of OM present. The lower the C:N, the more As released. Fe and ammonium release were similarly dependent on the quality and quantity of OM, but Fe mobilization was more rapid and ammonium release slower than As suggesting that the mobilization of these 3 moieties although interdependent, were not directly linked. It was concluded that low C:N ratios for OM responsible for reducing aquifers were As in groundwater is observed were likely.

Arsenic sequestration in iron plaque, its accumulation and speciation in mature rice plants (Oryza sativa L.)

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order: iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Codeposition of organic carbon and arsenic in Bengal Delta aquifers

We present data showing that arsenic (As) was codeposited with organic carbon (OC) in Bengal Delta sediments as As and OC concentrations are highly (p <0.001) positively correlated in core profiles collected from widely dispersed geographical sites with different sedimentary depositional histories. Analysis of modern day depositional environments revealed that the As-OC correlations observed in cores are due to As retention and high OC inputs in vegetated zones of the deltaic environment. We hypothesize that elevated concentrations of As occur in vegetated wetland sediments due to concentration and retention of arsenate in aerated root zones and animal burrows where copious iron(III) oxides are deposited. On burial of the sediment, degradation of organic carbon from plant and animal biomass detritus provides the reducing conditions to dissolve iron(III) oxides and release arsenite into the porewater. As tubewell abstracted aquifer water is an invaluable resource on which much of Southeast Asia is now dependent, this increased understanding of the processes responsible for As buildup and release will identify, through knowledge of the palaeosedimentary environment, which sediments are at most risk of having high arsenic concentrations in porewater. Our data allow the development of a new unifying hypothesis of how As is mobilized into groundwaters in river flood plains and deltas of Southeast Asia, namely that in these highly biologically productive environments, As and OC are codeposited, and the codeposited OC drives As release from the sediments.

Direct evidence showing the effect of root surface iron plaque on arsenite and arsenate uptake into rice (Oryza sativa) roots

The present study aimed to investigate the effects of root surface iron plaque on the uptake kinetics of arsenite and arsenate by excised roots of rice (Oryza sativa) seedlings. The results demonstrated that the presence of iron plaque enhanced arsenite and decreased arsenate uptake. Arsenite and arsenate uptake kinetics were adequately fitted by the Michaelis-Menten function in the absence of plaque, but produced poor fits to this function in the presence of plaque. Phosphate in the uptake solution did not have a significant effect on arsenite uptake irrespective of the presence of iron plaque; however phosphate had a significant effect on arsenate uptake. Without iron plaque, phosphate inhibited arsenate uptake. The presence of iron plaque diminished the effect of phosphate on arsenate uptake, possibly through a combined effect of arsenate desorption from iron plaque.