Neospora caninum is associated with abortion in Algerian cattle

Neospora caninum is a major cause of abortion in cattle worldwide. However, little information is available for Algeria. Accordingly, 799 cattle from 87 farms in the north and northeast of Algeria were enrolled in a seroepidemiological survey. An indirect fluorescence antibody test (IFAT) revealed a seroprevalence of 19.6%. The animals were divided into 3 groups according to their breed: imported European cattle, local breeds, and crossed animals (European × local). Seroprevalences were 16.0%, 34.3%, and 18.6% in groups 1, 2, and 3, respectively. A case control study was performed to investigate the link between global seropositivity to N. caninum and abortion risk in those cattle farms. There was a significant (P < 0.01) association between the seroprevalence against N. caninum and the occurrence of abortion in those farms (odds ratio [OR] = 12.03). This was also observed at the individual level (OR = 2.79). The analysis of results according to the breed revealed a significant association between seroprevalence and abortion in groups 1 and 3, but not for group 2, despite the fact that the highest seroprevalence was observed in group 2. Cerebral tissues from 5 aborted fetuses were available for histology and polymerase chain reaction (PCR). One sample was found positive both by histology and by PCR, 2 samples were positive by PCR only, and 2 samples were negative in both tests.     

The spread of<Emphasis Type="Italic"> Abies</Emphasis> throughout Europe since the last glacial period: combined macrofossil and pollen data

In this paper we reconstruct the location of the last glacial refugia and postglacial spread of Abies throughout Europe based on combined pollen and macrofossil data. More than 208 pollen sequences available in the European Pollen Database (EPD) and 38 macrofossil sites are used to produce distribution maps encompassing a time span between 38000 and 5500 years B.P. The investigation excludes more recent periods, because these could be strongly influenced by human impact. The pollen data presented here confirm long-lasting refugial areas such as southern Italy and Greece already described in previous studies. The combined pollen/macrofossil dataset identifies the Pyrenees as a further important refugium. In addition the pollen data indicate potential refugia in south-east France and north-west Italy. Possible migration tracks of Abies are discussed by comparing the palaeobotanical evidence with isozyme studies on gene markers of recent fir populations.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00334-004-0049-4.     

The papaya Kunitz-type trypsin inhibitor is a highly stable beta-sheet glycoprotein

The papaya Kunitz-type trypsin inhibitor, a 24-kDa glycoprotein, was purified to homogeneity. The purified inhibitor stoichiometrically inhibits bovine trypsin in a 1:1 molar ratio. Circular dichroism and infrared spectroscopy analyses demonstrated that the inhibitor contains extensive beta-sheet structures. The inhibitor was found to retain its full inhibitory activity over a broad pH range (1.5-11.0) and temperature (up to 80 degrees C), besides being stable at very high concentrations of strong chemical denaturants (e.g., 5.5 M guanidine hydrochloride). The inhibitor retained its compact structure over the pH range analyzed as shown by 8-anilino-1-naphtalenesulfonic acid binding characteristics, excluding the formation of some relaxed or molten state. Exposure to 2.5 mM dithiothreitol for 120 min caused a 33% loss of the inhibitory activity, while a loss of 75% was obtained in the presence of 20 mM of dithiothreitol during the same time period. A complete loss of the inhibitory activity was observed after incubation with 50 mM dithiothreitol for 5 min. Incubation of the inhibitor with general proteases belonging to different families revealed its extraordinary resistance to proteolysis in comparison with the soybean trypsin inhibitor, the archetypal member of the Kunitz-type inhibitors family. The inhibitor also exhibited a remarkable resistance to proteolytic degradation against pepsin for at least a 24-h incubation period. Instead, the soybean inhibitor was completely degraded after 2 h incubation with this aspartic protease. All these data demonstrated the high stability of the papaya trypsin inhibitor.     

Effects of drought stress on legume symbiotic nitrogen fixation: physiological mechanisms

Drought stress is one of the major factors affecting nitrogen fixation by legume-rhizobium symbiosis. Several mechanisms have been previously reported to be involved in the physiological response of symbiotic nitrogen fixation to drought stress, i.e. carbon shortage and nodule carbon metabolism, oxygen limitation, and feedback regulation by the accumulation of N fixation products. The carbon shortage hypothesis was previously investigated by studying the combined effects of CO2 enrichment and water deficits on nodulation and N2 fixation in soybean. Under drought, in a genotype with drought tolerant N2 fixation, approximately four times the amount of 14C was allocated to nodules compared to a drought sensitive genotype. It was found that an important effect of CO2 enrichment of soybean under drought was an enhancement of photo assimilation, an increased partitioning of carbon to nodules, whose main effect was to sustain nodule growth, which helped sustain N2 rates under soil water deficits. The interaction of nodule permeability to O2 and drought stress with N2 fixation was examined in soybean nodules and led to the overall conclusion that O2 limitation seems to be involved only in the initial stages of water deficit stresses in decreasing nodule activity. The involvement of ureides in the drought response of N2 fixation was initially suspected by an increased ureide concentration in shoots and nodules under drought leading to a negative feedback response between ureides and nodule activity. Direct evidence for inhibition of nitrogenase activity by its products, ureides and amides, supported this hypothesis. The overall conclusion was that all three physiological mechanisms are important in understanding the regulation of N2 fixation and its response of to soil drying.     

Narrow Bottlenecks Affect Pea Seedborne Mosaic Virus Populations during Vertical Seed Transmission but not during Leaf Colonization

The effective size of populations (Ne) determines whether selection or genetic drift is the predominant force shaping their genetic structure and evolution. Populations having high Ne adapt faster, as selection acts more intensely, than populations having low Ne, where random effects of genetic drift dominate. Estimating Ne for various steps of plant virus life cycle has been the focus of several studies in the last decade, but no estimates are available for the vertical transmission of plant viruses, although virus seed transmission is economically significant in at least 18% of plant viruses in at least one plant species. Here we study the co-dynamics of two variants of Pea seedborne mosaic virus (PSbMV) colonizing leaves of pea plants (Pisum sativum L.) during the whole flowering period, and their subsequent transmission to plant progeny through seeds. Whereas classical estimators of Ne could be used for leaf infection at the systemic level, as virus variants were equally competitive, dedicated stochastic models were needed to estimate Ne during vertical transmission. Very little genetic drift was observed during the infection of apical leaves, with Ne values ranging from 59 to 216. In contrast, a very drastic genetic drift was observed during vertical transmission, with an average number of infectious virus particles contributing to the infection of a seedling from an infected mother plant close to one. A simple model of vertical transmission, assuming a cumulative action of virus infectious particles and a virus density threshold required for vertical transmission to occur fitted the experimental data very satisfactorily. This study reveals that vertically-transmitted viruses endure bottlenecks as narrow as those imposed by horizontal transmission. These bottlenecks are likely to slow down virus adaptation and could decrease virus fitness and virulence.     

Biosynthesis of (R)-beta-tyrosine and its incorporation into the highly cytotoxic chondramides produced by Chondromyces crocatus

The chondramides are mixed non-ribosomal peptide/polyketide secondary metabolites produced by the myxobacterium Chondromyces crocatus Cm c5, which exhibit strong cytotoxic activity. On the basis of their striking structural similarity to the marine depsipeptides jaspamides, the chondramides have been assumed to incorporate a (R)-beta-tyrosine moiety, an expectation we confirm here. Thus, the recent sequencing of the chondramide biosynthetic gene cluster provided the opportunity to probe the shared origin of this unusual beta-amino acid. We demonstrate here that (R)-beta-tyrosine is produced directly from l-tyrosine by the aminomutase CmdF. Along with the tyrosine aminomutase SgcC4 from the C-1027 enediyne pathway, this enzyme belongs to a novel family of tyrosine aminomutases related to the ammonium lyase family of enzymes but exhibits opposite facial selectivity for the hydroxycinnamate intermediate. We also show that the adenylation (A) domain in the chondramide pathway, which activates the beta-tyrosine building block, exhibits the required preference for (R)-beta-tyrosine, further arguing against alternative origins for the moiety in the chondramides. Comparison to the (S)-beta-tyrosine specific A domain SgcC1 should enhance our understanding of the structural and stereochemical determinants guiding amino acid selection by non-ribosomal peptide synthetase multienzymes.     

Scaling up tests on virulence of the cassava green mite fungal pathogen <Emphasis Type="Italic">Neozygites tanajoae</Emphasis> (Entomophthorales: Neozygitaceae) under controlled conditions: first observations at the population level

Virulence of entomopathogens is often measured at the individual level using a single host individual or a group of host individuals. To what extent these virulence assessments reflect the impact of an entomopathogen on their host in the field remains largely untested, however. A methodology was developed to induce epizootics of the cassava green mite fungal pathogen Neozygites tanajoae under controlled conditions to evaluate population-level virulence of two (one Beninese and one Brazilian) isolates of the entomopathogen—which had shown similar individual-level virulence but different field impacts. In unrepeated separate experiments we inoculated mite-infested potted cassava plants with either 50 or 25 live mites (high and low inoculum) previously exposed to spores of N. tanajoae and monitored the development of fungal infections for each isolate under the same conditions. Both isolates caused mite infections and an associated decline in host mite populations relative to the control (without fungus) in all experiments, but prevalence of the fungus varied with isolate and increased with inoculum density. Peak infection levels were 90% for the Beninese isolate and 36% for the Brazilian isolate at high inoculum density, and respectively 17% and 25% at low inoculum density. We also measured dispersal from inoculated plants and found that spore dispersal increased with host infection levels, independent of host densities, whereas mite dispersal varied between isolates. These results demonstrate that epizootiology of N. tanajoae can be studied under controlled conditions and suggest that virulence tests at the population level may help to better predict performance of fungal isolates than individual-level tests.