A secreted serine-threonine kinase determines virulence in the eukaryotic pathogen Toxoplasma gondii

Toxoplasma gondii strains differ dramatically in virulence despite being genetically very similar. Genetic mapping revealed two closely adjacent quantitative trait loci on parasite chromosome VIIa that control the extreme virulence of the type I lineage. Positional cloning identified the candidate virulence gene ROP18, a highly polymorphic serine-threonine kinase that was secreted into the host cell during parasite invasion. Transfection of the virulent ROP18 allele into a nonpathogenic type III strain increased growth and enhanced mortality by 4 to 5 logs. These attributes of ROP18 required kinase activity, which revealed that secretion of effectors is a major component of parasite virulence.

Role of endothelium in dilator responses of spontaneously hypertensive rat arteries

The possible role of endothelium in the vascular responses to vasodilator drugs was studied in relation to experimental hypertension. Short ring segments of the thoracic aorta and femoral artery were removed from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. They were rubbed on the intimal surface to destruct endothelial cells or unrubbed, and bathed in Krebs-bicarbonate solution for isometric recording of contractile and relaxant responses. The relaxant response to acetylcholine was abolished by rubbing all arteries tested. Rubbing also significantly attenuated the relaxation induced by adenosine in the SHR aorta and SHR and WKY femoral artery, and attenuated the relaxation by isoproterenol in the SHR femoral artery. In contrast, contractile response to norepinephrine was augmented by intimal surface rubbing in all arteries except the aorta of WKY. It is suggested that an endothelial compensatory mechanism develops to offset the diminished relaxant and/or increased contractile responsiveness of smooth muscle cells in the hypertensive rat arteries.

Population structure and mouse-virulence of Toxoplasma gondii in Brazil

Recent studies found that isolates of Toxoplasma gondii from Brazil were biologically and genetically different from those in North America and Europe. However, to date only a small number of isolates have been analysed from different animal hosts in Brazil. In the present study DNA samples of 46 T. gondii isolates from cats in 11 counties in São Paulo state, Brazil were genetically characterised using 10 PCR restriction fragment length polymorphism markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico. An additional marker, CS3, that locates on chromosome VIIa and has previously been shown to be linked to acute virulence of T. gondii was also used to determine its association to virulence in mice. Genotyping of these 46 isolates revealed a high genetic diversity with 20 genotypes but no clonal Type I, II or III lineage was found. Two of the 46 isolates showed mixed infections. Combining genotyping data in this study with recent reported results from chickens, dogs and cats in Brazil (total 125 isolates) identified 48 genotypes and 26 of these genotypes had single isolates. Four of the 48 genotypes with multiple isolates identified from different hosts and locations are considered the common clonal lineages in Brazil. These lineages are designated as Types BrI, BrII, BrIII and BrIV. These results indicate that the T. gondii population in Brazil is highly diverse with a few successful clonal lineages expanded into wide geographical areas. In contrast to North America and Europe, where the Type II clonal lineage is overwhelmingly predominant, no Type II strain was identified from the 125 Brazil isolates. Analysis of mortality rates in infected mice indicates that Type BrI is highly virulent, Type BrIII is non-virulent, whilst Type BrII and BrIV lineages are intermediately virulent. In addition, allele types at the CS3 locus are strongly linked to mouse-virulence of the parasite. Thus, T. gondii has an epidemic population structure in Brazil and the major lineages have different biological traits.

Genotyping of Toxoplasma gondii by multilocus PCR-RFLP markers: a high resolution and simple method for identification of parasites

It was generally believed that Toxoplasma gondii had a clonal population structure with three predominant lineages, namely types I, II and III. This was largely based on genotyping of more than 100 T. gondii isolates originating from a variety of human and animal sources in North America and Europe. Recent genotyping studies on T. gondii strains from wild animals or human patients from different geographical regions revealed the high frequency of non-archetypal genotypes, suggesting the overall diversity of the T. gondii population might be much higher than we thought. However, as most genotyping studies had relied on a few biallelic markers, the resolution and discriminative power of identifying parasite isolates were quite low. To date, there is no commonly used set of markers to genotype T. gondii strains and it is not feasible to compare results from different laboratories. Here, we developed nine PCR-restriction fragment length polymorphism markers with each of them capable of distinguishing the three archetypal T. gondii alleles in one restriction-enzyme reaction by agarose gel electrophoresis. Genotyping 46 T. gondii isolates from different sources using these markers showed that they could readily distinguish the archetypal from atypical types and reveal the genetic diversity of the parasites. In addition, mixed strains in samples could be easily detected by these markers. Use of these markers will facilitate the identification of T. gondii isolates in epidemiological and population genetic studies.

Recent expansion of Toxoplasma through enhanced oral transmission

The global predominance of three clonal Toxoplasma gondii lineages suggests that they are endowed with an exceptional trait responsible for their current parasitism of nearly all warm-blooded vertebrates. Genetic polymorphism analyses indicate that these clonal lineages emerged within the last 10,000 years after a single genetic cross. Comparison with ancient strains (approximately 1 million years) suggests that the success of the clonal lineages resulted from the concurrent acquisition of direct oral infectivity. This key adaptation circumvented sexual recombination, simultaneously promoting transmission through successive hosts, hence leading to clonal expansion. Thus, changes in complex life cycles can occur rapidly and can profoundly influence pathogenicity.

Genetic diversity, clonality and sexuality in Toxoplasma gondii

The majority of Toxoplasma gondii strains from a variety of human and animal sources have been grouped into three highly clonal but closely related lineages. The low occurrence of nucleotide differences among the three predominant lineages and their unusual dimorphic allelic composition suggest that they have arisen from a recent common ancestry. Less than 1% of the previously studied strains contain unique genotypes and high divergence of DNA sequence, and therefore are considered 'exotic' or 'atypical' strains. The seemingly low genetic diversity in T. gondii may have been underestimated because most parasite strains in previous studies were collected from human patients and domestic animals in North America and Europe. To investigate the genetic diversity of T. gondii, we analysed parasite strains isolated from remote geographical regions by multilocus microsatellite sequencing and phylogenetic analysis. The genetic diversity indices, the molecular analysis of microsatellite genotypes and the constructed phylogram considered together suggest that the global T. gondii population is highly diversified and not characteristic of a clonal organism. The most parsimonious hypothesis is that T. gondii presents a complex population structure with a mix of clonal and sexual propagation as a function of the environmental conditions. The comparison between domestic strains data on one hand and wild strains data on the other hand is in favour of more frequent sexual recombinations in wild environment even though Toxoplasma subpopulation in human and domestic animals is largely clonal.

Arsenate and arsenite removal by zerovalent iron: effects of phosphate, silicate, carbonate, borate, sulfate, chromate, molybdate, and nitrate, relative to chloride

Batch tests were performed to evaluate the effects of inorganic anion competition on the kinetics of arsenate (As(V)) and arsenite (As(III)) removal by zerovalent iron (Peerless Fe0) in aqueous solution. The oxyanions underwent either sorption-dominated reactions (phosphate, silicate, carbonate, borate, and sulfate) or reduction-dominated reactions (chromate, molybdate, and nitrate) with Peerless Fe0 in the presence of As(V) or As(III), relative to chloride. Pseudo-first-order rate equations were found to describe satisfactorily both As(V) and As(III) removal kinetics in the presence of each competing anion. Of the oxyanions tested for Peerless Fe0 in the pH range from 7 to 9, phosphate caused the greatest decrease in As removal rate (7.0 x 10(-3) to 18.5 x 10(-3) h(-1)) relative to chloride (34.9 x 10(-3) to 36.2 x 10(-3) h(-1)). Silicate, chromate, and molybdate also caused strong inhibition of As removal, followed by carbonate and nitrate, whereas borate and sulfate only caused slight inhibition to As(III) removal. Present results show that Peerless Fe0 may be an excellent permeable reactive barrier medium for a suite of mixed inorganic contaminants. The anion competing effects should be considered when designing permeable reactive barriers composed of zerovalent iron for field applications to remediate As(V) and As(III).

Escherichia coli O157:H7 infection in humans

OBJECTIVE

To review the clinical relevance of Escherichia coli O157:H7 infection, including the epidemiology of the infection and its clinical presentations, pathogenesis, microbiology, diagnosis, treatment, and prevention.

DATA SOURCES

Articles on E. coli O157:H7 were identified through MEDLINE and the bibliographies of relevant articles.

STUDY SELECTION

All articles and case reports describing E. coli O157:H7 and its infection were selected.

DATA EXTRACTION

The data were abstracted without judgments about study design. Data quality and validity were assessed by independent author reviews.

DATA SYNTHESIS

Infection with E. coli O157:H7 presents with a wide spectrum of clinical manifestations, including asymptomatic carriage, nonbloody diarrhea, hemorrhagic colitis, the hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura. Not only is E. coli O157:H7 an important agent for hemorrhagic colitis, it is also one of the leading causes of bacterial diarrhea. Patients at extremes of age have an increased risk for infection and associated complications. Transmission of E. coli O157:H7 is primarily food-borne. Undercooked meat is the most common culprit, and secondary person-to-person spread is also important. The organism produces at least two Shiga-like toxins that differ antigenically, physicochemically, immunologically, and in their biological effects. These toxins are thought to have direct pathogenic significance in E. coli O157:H7 infection. This infection is usually diagnosed from a positive stool culture, from the presence of Shiga-like toxins, or both. Timely collection (within 7 days of illness onset) of a stool sample for culture is imperative for a high recovery rate. Treatment is primarily supportive and includes the management of complications as necessary. Antibiotic therapy has not been proved beneficial. Important public health measures include educating the public on the danger of eating undercooked meat, increasing physician awareness of E. coli O157:H7 infection, and mandating case reporting.

CONCLUSIONS

Infection with E. coli O157:H7 presents with many clinical manifestations and should be included in the differential diagnosis for any patient with new-onset bloody diarrhea. Development of the hemolytic-uremic syndrome or thrombotic thrombocytopenic purpura should raise strong suspicion of E. coli O157:H7 infection and should lead to prompt evaluation. If infection is confirmed, it should be reported to public health officials.

[3H]adenosine triphosphate: release during stimulation of enteric nerves

The isolated taenia coli of the guinea pig takes up tritiated adenosine, adenosine monophosphate, adenosine diphosphate, and adenosine triphosphate, in preference to tritiated inosine and adenine. After uptake, [(3)H]adenosine is converted and retained primarily as [(3)H]adenosine triphosphate. Tritium is released from taenia coli treated with [(3)H]adenosine upon activation of the nonadrenergic inhibitory nerves. These results are consistent with the previous evidence that adenosine triphosphate may be the transmitter from the nerves.

The physical activity transition among adults in China: 1991-2011

Previous studies have linked work, home production, travel activities and inactivity with weight and health outcomes. However, these focused on average physical activity (PA) over time rather than changes in PA and associated sociodemographic and economic factors and urbanicity. Using the 1991-2011 China Health and Nutrition Survey data, we estimated the metabolic equivalent of task hours per week for individuals in occupational, domestic, travel and active leisure domains and sedentary hours per week. We present the distributions among adult men and women (aged 18-60), and use quantile regression models to explore factors associated with these trends. Trend analyses on the distribution of PA show declines along the whole distribution of occupational PA for men and women and domestic PA for women in China. These patterns remain consistent after adjusting for individual- and household-level factors. Controlling for urbanicity mitigated the decrease in occupational PA, particularly for men, but not the decrease in domestic PA. Given China's rapid urbanization and its association with occupational PA declines and the strong time trend in domestic PA, there is a need to invest in interventions and policies that promote PA during leisure and travel times.

High prevalence and abundant atypical genotypes of Toxoplasma gondii isolated from lambs destined for human consumption in the USA

Little information is available on the presence of viable Toxoplasma gondii in tissues of lambs worldwide. The prevalence of T. gondii was determined in 383 lambs (<1 year old) from Maryland, Virginia and West Virginia, USA. Hearts of 383 lambs were obtained from a slaughter house on the day of killing. Blood removed from each heart was tested for antibodies to T. gondii by using the modified agglutination test (MAT). Sera were first screened using 1:25, 1:50, 1: 100 and 1:200 dilutions, and hearts were selected for bioassay for T. gondii. Antibodies (MAT, 1:25 or higher) to T. gondii were found in 104 (27.1%) of 383 lambs. Hearts of 68 seropositive lambs were used for isolation of viable T. gondii by bioassay in cats, mice or both. For bioassays in cats, the entire myocardium or 500g was chopped and fed to cats, one cat per heart and faeces of the recipient cats were examined for shedding of T. gondii oocysts. For bioassays in mice, 50g of the myocardium was digested in an acid pepsin solution and the digest inoculated into mice; the recipient mice were examined for T. gondii infection. In total, 53 isolates of T. gondii were obtained from 68 seropositive lambs. Genotyping of the 53 T. gondii isolates using 10 PCR-restriction fragment length polymorphism markers (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico) revealed 57 strains with 15 genotypes. Four lambs had infections with two T. gondii genotypes. Twenty-six (45.6%) strains belong to the clonal Type II lineage (these strains can be further divided into two groups based on alleles at locus Apico). Eight (15.7%) strains belong to the Type III lineage. The remaining 22 strains were divided into 11 atypical genotypes. These results indicate high parasite prevalence and high genetic diversity of T. gondii in lambs, which has important implications in public health. We believe this is the first in-depth genetic analysis of T. gondii isolates from sheep in the USA.

Recent transcontinental sweep of Toxoplasma gondii driven by a single monomorphic chromosome

Toxoplasma gondii is a highly prevalent protozoan parasite that infects a wide range of animals and threatens human health by contaminating food and water. A markedly limited number of clonal parasite lineages have been recognized as predominating in North American and European populations, whereas strains from South America are comparatively diverse. Here, we show that strains from North America and Europe share distinct genetic polymorphisms that are mutually exclusive from polymorphisms in strains from the south. A striking exception to this geographic segregation is a monomorphic version of one chromosome (Chr1a) that characterizes virtually all northern and many southern isolates. Using a combination of molecular phylogenetic and phenotypic analyses, we conclude that northern and southern parasite populations diverged from a common ancestor in isolation over a period of approximately 10(6) yr, and that the monomorphic Chr1a has swept each population within the past 10,000 years. Like its definitive feline hosts, T. gondii may have entered South America and diversified there after reestablishment of the Panamanian land bridge. Since then, recombination has been an infrequent but important force in generating new T. gondii genotypes. Genes unique to a monomorphic version of a single parasite chromosome may have facilitated a recent population sweep of a limited number of highly successful T. gondii lineages.

Genotyping of Toxoplasma gondii strains from immunocompromised patients reveals high prevalence of type I strains

Toxoplasma gondii is an important food- and waterborne opportunistic pathogen that causes severe disease in immunocompromised patients. T. gondii has an unusual clonal population structure consisting of three widespread lineages known as I, II, and III. To establish the genotypes of strains of T. gondii associated with human toxoplasmosis, we have developed a set of four highly sensitive and polymorphic nested PCR markers. Multiplex nested PCR analysis was used to genotype parasites in cerebral spinal fluid samples from 8 of 10 human immunodeficiency virus-positive patients. Remarkably, a majority of these patients had infections with type I strains or strains containing type I alleles, despite the fact that this lineage is normally uncommon in humans and animals. Multiplex analysis of these four unlinked makers was able to distinguish all three common genotypes and also detected two strains with mixed genotypes. Further analysis based on sequencing of a polymorphic intron revealed that one of these recombinant strains was an exotic lineage distinct from the archetypal clonal lineages. The multiplex nested PCR analysis described here will be useful for analyzing the contribution of parasite genotype to toxoplasmosis.

The proinflammatory cytokine, interleukin-1alpha, reduces glucocorticoid receptor translocation and function

Proinflammatory cytokines have been shown to influence the expression and function of the glucocorticoid receptor (GR). Specifically, several studies have found that cytokines induce a decrease in GR function, as evidenced by reduced sensitivity to glucocorticoid effects on functional end points. To investigate the potential mechanism(s) involved, we examined the impact of the proinflammatory cytokine, interleukin-1alpha (IL-1alpha), on 1) GR translocation from cytoplasm to nucleus using GR immunostaining, 2) cytosolic radioligand GR binding, and 3) GR-mediated gene transcription in L929 cells stably transfected with the mouse mammary tumor virus-cholamphenicol acetyltransferase reporter gene. L929 cells were treated with IL-1alpha (100 and 1000 U/ml) for 24 h in the presence or absence of dexamethasone (Dex; 10 nM to 1 microM). IL-1alpha inhibited Dex-induced GR translocation and alone induced GR up-regulation. Pretreatment with IL-1alpha followed by Dex treatment for 1.5 h led to about 20% inhibition of Dex-induced GR-mediated gene transcription, whereas coincubation of IL-1alpha plus Dex for 24 h inhibited Dex-induced GR-mediated gene activity up to 42%. The latter effect was reversed by the IL-1 receptor antagonist. These results suggest that cytokines produced during an inflammatory response may induce GR resistance in relevant cell types by direct effects on the GR, thereby providing an additional pathway by which the immune system can influence the hypothalamic-pituitary-adrenal axis.

Genetic characterisation of Toxoplasma gondii in wildlife from North America revealed widespread and high prevalence of the fourth clonal type

Little is known of the genetic diversity of Toxoplasma gondii circulating in wildlife. In the present study wild animals, from the USA were examined for T. gondii infection. Tissues of naturally exposed animals were bioassayed in mice for isolation of viable parasites. Viable T. gondii was isolated from 31 animals including, to our knowledge for the first time, from a bald eagle (Haliaeetus leucocephalus), five gray wolves (Canis lupus), a woodrat (Neotoma micropus), and five Arctic foxes (Alopex lagopus). Additionally, 66 T. gondii isolates obtained previously, but not genetically characterised, were revived in mice. Toxoplasma gondii DNA isolated from these 97 samples (31+66) was characterised using 11 PCR-restriction fragment length polymorphism (RFLP) markers (SAG1, 5'- and 3'-SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico). A total of 95 isolates were successfully genotyped. In addition to clonal Types II, and III, 12 different genotypes were found. These genotype data were combined with 74 T. gondii isolates previously characterised from wildlife from North America and a composite data set of 169 isolates comprised 22 genotypes, including clonal Types II, III and 20 atypical genotypes. Phylogenetic network analysis showed limited diversity with dominance of a recently designated fourth clonal type (Type 12) in North America, followed by the Type II and III lineages. These three major lineages together accounted for 85% of strains in North America. The Type 12 lineage includes previously identified Type A and X strains from sea otters. This study revealed that the Type 12 lineage accounts for 46.7% (79/169) of isolates and is dominant in wildlife of North America. No clonal Type I strain was identified among these wildlife isolates. These results suggest that T. gondii strains in wildlife from North America have limited diversity, with the occurrence of only a few major clonal types.

Manganese lipoxygenase. Purification and characterization

A linoleic acid (13R)-lipoxygenase was purified to homogeneity from the culture medium of Gäumannomyces graminis, the take-all fungus, by hydrophobic interaction, cation exchange, lectin affinity, and size-exclusion chromatography. The purified dioxygenase lacked light absorption between 300 and 700 nm. Gel filtration indicated an apparent molecular mass of approximately 135 kDa in 6 M urea and approximately 160 kDa in buffer. SDS-polyacrylamide gel electrophoresis (PAGE) showed that the enzyme was heterogeneous in size and consisted of diffuse protein bands of 100-140 kDa. Treatment with glycosidases for N- and O-linked oligosaccharides yielded a distinct protein of approximately 73 kDa on SDS-PAGE. Atomic emission spectroscopy indicated 0.5-1.0 manganese atom/enzyme molecule. The isoelectric point was approximately 9.7, and the enzyme was active between pH 5 and 11 with optimum activity at pH 7. 0. For molecular oxygen, Km was 30 microM and Vmax 10 micromol mg-1min-1; for linoleic acid, Km was 4.4 micromol, Vmax 8.2 micromol mg-1min-1, and the turnover number 1100 min-1. The enzyme oxidized linolenic acid twice as fast as linoleic acid. The main products were identified by mass spectrometry as 13-hydroperoxy-(9Z,11E, 15Z)-octadecatrienoic and 13-hydroperoxy-(9Z,11E)-octadecadienoic acids, respectively. After reduction of the hydroperoxide, steric analysis of methyl 13-hydroxyoctadecadienoate by chiral high performance liquid chromatography yielded one enantiomer (>95%), which co-eluted with the R-stereoisomer of methyl (13R, 13S)-hydroxyoctadecadienoate. Arachidonic and dihomogammalinolenic acids were not substrates, while oxygen consumption, UV analysis, and mass spectrometric analysis indicated that gamma-linolenic acid was oxygenated both at C-11 and C-13. The enzyme was active at 60 degreesC and after treatment with 6 M urea. It was strongly inhibited by 10-50 microM concentrations of eicosatetraynoic acid and a lipoxygenase inhibitor (N-(3-phenoxycinnamyl)acetohydroxamic acid), but many other lipoxygenase inhibitors (100 microM) were without effect. We conclude that, after deglycosylation, the enzyme has the same size on SDS-PAGE as mammalian and marine lipoxygenases, but it differs from all previously described lipoxygenases in three ways. It is secreted, it forms (13R)-hydroperoxy-(9Z, 11E)-octadecadienoic acid, and it contains manganese.

Biologic and genetic comparison of Toxoplasma gondii isolates in free-range chickens from the northern Pará state and the southern state Rio Grande do Sul, Brazil revealed highly diverse and distinct parasite populations

The prevalence of Toxoplasma gondii in 84 free-range chickens (34 from the northern Pará state, and 50 from Rio Grande do Sul, the southern state) from Brazil, South America was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT), and found in 39 (46.4%) of 84 chickens with titers of 1:10 in one, 1:20 in two, 1:40 in four, 1:80 in seven, 1:160 in five, 1:320 in six, 1:640 in eight and > or =1:1280 in six. Hearts and brains of 45 chickens with titers of 1:20 or less were pooled and fed to two T. gondii-free cats. Hearts and brains of 39 chickens with titers of 1:10 or higher were bioassayed in mice. Feces of cats were examined for oocysts. One cat fed tissues from 31 chickens with titers of less than 1:10 from Rio Grande do Sul shed T. gondii oocysts. T. gondii was isolated by bioassay in mice from 33 chickens with MAT titers of 1:20 or higher. All infected mice from 10 isolates died of toxoplasmosis. All 34 isolates (15 from Pará, 19 from Rio Grande do Sul) were genotyped using 11 genetic markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, a new SAG2 and Apico. Eleven genotypes were revealed for Pará isolates and seven genotypes for Rio Grande do Sul. No genotype was shared between the two geographical locations. These data suggest that T. gondii isolates are highly diverse and genetically distinct between the two different regions in Brazil that are 3500 km apart.

Endothelium removal augments vasodilation by sodium nitroprusside and sodium nitrite

Sodium nitroprusside (3-100 nM) and sodium nitrite (0.03-1 mM) caused relaxation of the rat aortic ring segments precontracted by norepinephrine. The relaxation was significantly augmented by removal of endothelium, and this augmentation was greater in the aorta from spontaneously hypertensive rats (SHR) than Wistar Kyoto rats (WKY). The mechanism remains unknown but such augmentation may be clinically favorable to the use of nitrovasodilators.

Manganese lipoxygenase. Discovery of a bis-allylic hydroperoxide as product and intermediate in a lipoxygenase reaction

Linoleic acid was incubated with manganese lipoxygenase (Mn-LO) from the fungus Gäumannomyces graminis. The product consisted of (13R)-hydroperoxy-(9Z,11E)-octadecadienoic acid ((13R)-HPOD) and a new hydroperoxide, (11S)-hydroperoxy-(9Z,12Z)-octadecadienoic acid ((11S)-HPOD). Incubation of (11R)-[2H]- and (11S)-[2H]linoleic acids with Mn-LO led to the formation of hydroperoxides that largely retained and lost, respectively, the deuterium label. Conversion of the (11S)-deuteriolinoleic acid was accompanied by a primary isotope effect, which manifested itself in a strongly reduced rate of formation of hydroperoxides and in a time-dependent accumulation of deuterium in the unconverted substrate. These experiments indicated that the initial step catalyzed by Mn-LO consisted of abstraction of the pro-S hydrogen of linoleic acid to produce a linoleoyl radical. (11S)-HPOD was converted into (13R)-HPOD upon incubation with Mn-LO. The mechanism of this enzyme-catalyzed hydroperoxide rearrangement was studied in experiments carried out with 18O2 gas or 18O2-labeled hydroperoxides. Incubation of [11-18O2](11S)-HPOD with Mn-LO led to the formation of (13R)-HPOD, which retained 39-44% of the 18O label, whereas (11S)-HPOD incubated with Mn-LO under 18O2 produced (13R)-HPOD, which had incorporated 57% of 18O. Furthermore, analysis of the isotope content of (11S)-HPOD remaining unconverted in such incubations demonstrated that [11-18O2](11S)-HPOD suffered a time-dependent loss of 18O when exposed to Mn-LO, whereas (11S)-HPOD incorporated 18O when incubated with Mn-LO under 18O2. On the basis of these experiments, it was proposed that the conversion of (11S)-HPOD into (13R)-HPOD occurred in a non-concerted way by deoxygenation into a linoleoyl radical. Subsequent reoxygenation of this intermediate by dioxygen attack at C-13 produced (13R)-HPOD, whereas attack at C-11 regenerated (11S)-HPOD. The hydroperoxide rearrangement occurred by oxygen rebound, although, as demonstrated by the 18O experiments, the oxygen molecule released from (11S)-HPOD exchanged with surrounding molecular oxygen prior to its reincorporation.

Genetic and biologic characterization of Toxoplasma gondii isolates of cats from China

Cats are important in the epidemiology of Toxoplasma gondii infection because they are the only hosts that can excrete the environmentally resistant oocysts. In the present study, prevalence of T. gondii was determined in serum, feces, and tissues of 34 cats from People's Republic of China. Antibodies to T. gondii were assayed by the modified agglutination test and found in 27 of 34 (79.4%) cats with titers of 1:40 in one, 1:80 in one, 1:160 in three, 1:320 in three, 1:640 in eight, and 1:1280 or higher in 11 cats. T. gondii oocysts were not found in feces of any cat as ascertained by bioassay in mice. Tissues (brain, heart, and tongue) of 27 seropositive cats were pooled and bioassayed in mice (8 cats) or cats (19 cats). T. gondii was isolated from tissues of 17 of 27 seropositive cats. Genotyping of these 17 T. gondii isolates using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and a new SAG2, and an apicoplast marker Apico revealed two genotypes. This is the first report of genetic typing of T. gondii isolates from cats from China.

Neurogenic vasodilation of cat cerebral arteries

Transmural nerve stimulation (TNS) with 0.3-msec pulses between 1 and 25 Hz dilated cat cerebral artery segments in the presence of active muscle tone. Maximum vasodilatation occurred at 8 Hz. The dilator response to exogenous acetylcholine, but not to TNS, was abolished by atropine. Neither physostigmine nor hemicholinium affected the dilator response to TNS, which persisted after administration of guanethidine, phenoxybenzamine, propranolol, reserpine, and chronic sympathectomy. However, it was abolished by tetrodotoxin and cold storage. When examined histochemically, cat and rabbit cerebral arteries exhibited a rich plexiform distribution of acetylcholinesterase which was not affected appreciably by sympathetic denervation. These results suggest that vasodilation is not mediated through modification of sympathetic activity. They also indicate the existence of a nonadrenergic, possibly noncholinergic, vasodilator innervation in cat cerebral arteries. Preliminary studies suggest that the transmitter is not histamine, ATP, prostaglandins, gamma-aminobutyric acid, dopamine, or serotonin. The cat cerebral artery segments contrast with the isolated rabbit cerebral arteries which predominantly constrict in response to TNS and show a small dilator response.

Genetic diversity of Toxoplasma gondii isolates from chickens from Brazil

Until recently, Toxoplasma gondii was considered clonal with very little genetic variability. Recent studies indicate that T. gondii isolates from Brazil are genetically and biologically different from T. gondii isolates from USA and Europe. In the present study, we retyped 151 free range chicken isolates from Brazil including 117 newly isolated samples from 11 geographically areas (Alagoas, Bahia, Ceará, Maranhão, Paraná, Pernambuco, Rio de Janeiro, Rio Grande do Norte, São Paulo, Sergipe, and Rondonia) and 34 previously reported isolates from the very north (Pará) and the very south (Rio Grande do Sul). Ten PCR-RFLP markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico were used to genotype all isolates. Overall analysis of 151 T. gondii isolates revealed 58 genotypes. Half (29/58) of these genotypes had single isolate and the other half of the genotypes were characterized with two or more isolates. Only 1 of 151 isolates was clonal Type I strain and 5 were clonal Type III strains. Two isolates had mixed infections. Clonal Type II strain was absent. One strain was Type II at all loci, except BTUB. The results confirm high genetic diversity of T. gondii isolates from Brazil.

Arsenate and arsenite removal by zerovalent iron: kinetics, redox transformation, and implications for in situ groundwater remediation

Batch tests were performed utilizing four zerovalent iron (Fe0) filings (Fisher, Peerless, Master Builders, and Aldrich) to remove As(V) and As(III) from water. One gram of metal was reacted headspace-free at 23 degrees C for up to 5 days in the dark with 41.5 mL of 2 mg L(-1) As(V), or As(III) or As(V) + As(III) (1:1) in 0.01 M NaCl. Arsenic removal on a mass basis followed the order: Fisher > Peerless Master Builders > Aldrich; whereas, on a surface area basis the order became: Fisher > Aldrich > Peerless Master Builders. Arsenic concentration decreased exponentially with time, and was below 0.01 mg L(-1) in 4 days with the exception of Aldrich Fe0. More As(III) was sorbed than As(V) by Peerless Fe0 in the initial As concentration range between 2 and 100 mg L(-1). No As(III) was detected by X-ray photoelectron spectroscopy (XPS) on Peerless Fe0 at 5 days when As(V) was the initial arsenic species in the solution. As(III) was detected by XPS at 30 and 60 days present on Peerless Fe0, when As(V) was the initial arsenic species in the solution. Likewise, As(V) was found on Peerless Fe0 when As(II) was added to the solution. A steady distribution of As(V) (73-76%) and As(III) (22-25%) was achieved at 30 and 60 days on the Peerless Fe0 when either As(V) or As(III) was the initial added species. The presence of both reducing species (Fe0 and Fe2+) and an oxidizing species (MnO2) in Peerless Fe0 is probably responsible for the coexistence of both As(V) and As(III) on Fe0 surfaces. The desorption of As(V) and As(III) by phosphate extraction decreased as the residence time of interaction between the sorbents and arsenic increased from 1 to 60 days. The results suggest that both As(V) and As(III) formed stronger surface complexes or migrated further inside the interior of the sorbent with increasing time.