Variability of composition and effects of essential oils from Rhanterium adpressum Coss. & Durieu against mycotoxinogenic Fusarium strains

The antifungal potency of the essential oils of Rhanterium adpressum was evaluated against four mycotoxigenic strains of the genus Fusarium. The essential oils were obtained, separately, by hydro-distillation of the aerial parts of R. adpressum (leaves and flowers). The parts were collected during the period of bloom (3 months) for 3 years. The GC-MS analysis revealed thirty-six compounds for the essential oils, divided into four classes of chemical compounds, with variable percentages according to the month of extraction. The monoterpene hydrocarbons form the main class in these oils. On the other hand, the highest percentages of the oxygenated compounds are observed in the samples collected during the month of May. The direct contact method was used to evaluate the antifungal activity of the essential oils. The activity can be attributed to their relatively high composition of oxygenated monoterpenes. Flowers extract showed strong inhibitory activity, with very interesting concentrations of IC50 and MIC for both tests on solid and liquid medium. The effect of these oils on the production of type B trichothecenes (TCTBs) was evaluated, showing a significant inhibitory effect on TCTBs production, for both extracts (leaves and flowers). The rates of inhibition were 66-97 and 76-100% of FX, 3-ADON and 15-ADON, respectively. The inhibition of fungal biomass and the production of TCTBs depended on the used concentration of the essential oils. These results suggest that the essential oils from R. adpressum are able to control the growth of the tested strains and their subsequent production of TCTB mycotoxins.

Abiotic conditions leading to FUM gene expression and fumonisin accumulation by Fusarium proliferatum strains grown on a wheat-based substrate

Fusarium proliferatum produces fumonisins B not only on maize but also on diverse crops including wheat. Using a wheat-based medium, the effects of abiotic factors, temperature and water activity (a_W), on growth, fumonisin biosynthesis, and expression of FUM genes were compared for three F. proliferatum strains isolated from durum wheat in Argentina. Although all isolates showed similar profiles of growth, the fumonisin production profiles were slightly different. Regarding FUM gene transcriptional control, both FUM8 and FUM19 expression showed similar behavior in all tested conditions. For both genes, expression at 25°C correlated with fumonisin production, regardless of the a_w conditions. However, at 15°C, these two genes were as highly expressed as at 25°C although the amounts of toxin were very weak, suggesting that the kinetics of fumonisin production was slowed at 15°C. This study provides useful baseline data on conditions representing a low or a high risk for contamination of wheat kernels with fumonisins.

Landscape of genomic diversity and host adaptation in Fusarium graminearum

BACKGROUND

Fusarium graminearum is one of the main causal agents of the Fusarium Head Blight, a worldwide disease affecting cereal cultures, whose presence can lead to contaminated grains with chemically stable and harmful mycotoxins. Resistant cultivars and fungicides are frequently used to control this pathogen, and several observations suggest an adaptation of F. graminearum that raises concerns regarding the future of current plant disease management strategies. To understand the genetic basis as well as the extent of its adaptive potential, we investigated the landscape of genomic diversity among six French isolates of F. graminearum, at single-nucleotide resolution using whole-genome re-sequencing.

RESULTS

A total of 242,756 high-confidence genetic variants were detected when compared to the reference genome, among which 96% are single nucleotides polymorphisms. One third of these variants were observed in all isolates. Seventy-seven percent of the total polymorphism is located in 32% of the total length of the genome, comprising telomeric/subtelomeric regions as well as discrete interstitial sections, delineating clear variant enriched genomic regions- 7.5 times in average. About 80% of all the F. graminearum protein-coding genes were found polymorphic. Biological functions are not equally affected: genes potentially involved in host adaptation are preferentially located within polymorphic islands and show greater diversification rate than genes fulfilling basal functions. We further identified 29 putative effector genes enriched with non-synonymous effect mutation.

CONCLUSIONS

Our results highlight a remarkable level of polymorphism in the genome of F. graminearum distributed in a specific pattern. Indeed, the landscape of genomic diversity follows a bi-partite organization of the genome according to polymorphism and biological functions. We measured, for the first time, the level of sequence diversity for the entire gene repertoire of F. graminearum and revealed that the majority are polymorphic. Those assumed to play a role in host-pathogen interaction are discussed, in the light of the subsequent consequences for host adaptation. The annotated genetic variants discovered for this major pathogen are valuable resources for further genetic and genomic studies.

Patulin is a cultivar-dependent aggressiveness factor favouring the colonization of apples by Penicillium expansum

The blue mould decay of apples is caused by Penicillium expansum and is associated with contamination by patulin, a worldwide regulated mycotoxin. Recently, a cluster of 15 genes (patA-patO) involved in patulin biosynthesis was identified in P. expansum. blast analysis revealed that patL encodes a Cys6 zinc finger regulatory factor. The deletion of patL caused a drastic decrease in the expression of all pat genes, leading to an absence of patulin production. Pathogenicity studies performed on 13 apple varieties indicated that the PeΔpatL strain could still infect apples, but the intensity of symptoms was weaker compared with the wild-type strain. A lower growth rate was observed in the PeΔpatL strain when this strain was grown on nine of the 13 apple varieties tested. In the complemented PeΔpatL:patL strain, the ability to grow normally in apple and the production of patulin were restored. Our results clearly demonstrate that patulin is not indispensable in the initiation of the disease, but acts as a cultivar-dependent aggressiveness factor for P. expansum. This conclusion was strengthened by the fact that the addition of patulin to apple infected by the PeΔpatL mutant restored the normal fungal colonization in apple.

Antioxidant Secondary Metabolites in Cereals: Potential Involvement in Resistance to Fusarium and Mycotoxin Accumulation

Gibberella and Fusarium Ear Rot and Fusarium Head Blight are major diseases affecting European cereals. These diseases are mainly caused by fungi of the Fusarium genus, primarily Fusarium graminearum and Fusarium verticillioides. These Fusarium species pose a serious threat to food safety because of their ability to produce a wide range of mycotoxins, including type B trichothecenes and fumonisins. Many factors such as environmental, agronomic or genetic ones may contribute to high levels of accumulation of mycotoxins in the grain and there is an urgent need to implement efficient and sustainable management strategies to reduce mycotoxin contamination. Actually, fungicides are not fully efficient to control the mycotoxin risk. In addition, because of harmful effects on human health and environment, their use should be seriously restricted in the near future. To durably solve the problem of mycotoxin accumulation, the breeding of tolerant genotypes is one of the most promising strategies for cereals. A deeper understanding of the molecular mechanisms of plant resistance to both Fusarium and mycotoxin contamination will shed light on plant-pathogen interactions and provide relevant information for improving breeding programs. Resistance to Fusarium depends on the plant ability in preventing initial infection and containing the development of the toxigenic fungi while resistance to mycotoxin contamination is also related to the capacity of plant tissues in reducing mycotoxin accumulation. This capacity can result from two mechanisms: metabolic transformation of the toxin into less toxic compounds and inhibition of toxin biosynthesis. This last mechanism involves host metabolites able to interfere with mycotoxin biosynthesis. This review aims at gathering the latest scientific advances that support the contribution of grain antioxidant secondary metabolites to the mechanisms of plant resistance to Fusarium and mycotoxin accumulation.

Is the Fgap1 mediated response to oxidative stress chemotype dependent in Fusarium graminearum?

This study aims to compare the role of the transcription factor Fgap1 in oxidative stress response for two Fusarium graminearum strains belonging to the two chemotypes DON/ADON and NIV/FX. While the response to H2O2 was shown to be chemotype dependent, an opposite result was observed for diamide: whatever the chemotype, the global level of TCTB (i.e. trichothecene B) production was strongly increased by the treatment with diamide. Fgap1 was shown to be involved in this regulation for both chemotypes. Our data show that the response to diamide is mediated by Fgap1 whatever the chemotype of the F. graminearum strains. However, the NIV/FX chemotype has developed higher antioxidant capacities in response to oxidative stress. But when this capacity is overwhelmed by an increment in the H2O2 level, the NIV/FX strains also responds by an increase in toxin accumulation.

Bioguided isolation, characterization, and biotransformation by Fusarium verticillioides of maize kernel compounds that inhibit fumonisin production

Fusarium verticillioides infects maize ears, causing ear rot disease and contamination of grain with fumonisin mycotoxins. This contamination can be reduced by the presence of bioactive compounds in kernels that are able to inhibit fumonisin biosynthesis. To identify such compounds, we used kernels from a maize genotype with moderate susceptibility to F. verticillioides, harvested at the milk-dough stage (i.e., when fumonisin production initiates in planta), and applied a bioguided fractionation approach. Chlorogenic acid was the most abundant compound in the purified active fraction and its contribution to fumonisin inhibitory activity was up to 70%. Moreover, using a set of maize genotypes with different levels of susceptibility, chlorogenic acid was shown to be significantly higher in immature kernels of the moderately susceptible group. Altogether, our data indicate that chlorogenic acid may considerably contribute to either maize resistance to Fusarium ear rot, fumonisin accumulation, or both. We further investigated the mechanisms involved in the inhibition of fumonisin production by chlorogenic acid and one of its hydrolyzed products, caffeic acid, by following their metabolic fate in supplemented F. verticillioides broths. Our data indicate that F. verticillioides was able to biotransform these phenolic compounds and that the resulting products can contribute to their inhibitory activity.

The bZIP transcription factor Fgap1 mediates oxidative stress response and trichothecene biosynthesis but not virulence in Fusarium graminearum

Redox sensing is of primary importance for fungi to cope with oxidant compounds found in their environment. Plant pathogens are particularly subject to the oxidative burst during the primary steps of infection. In the budding yeast Saccharomyces cerevisiae, it is the transcription factor Yap1 that mediates the response to oxidative stress via activation of genes coding for detoxification enzymes. In the cereal pathogen Fusarium graminearum, Fgap1 a homologue of Yap1 was identified and its role was investigated. During infection, this pathogen produces mycotoxins belonging to the trichothecenes family that accumulate in the grains. The global regulation of toxin biosynthesis is not completely understood. However, it is now clearly established that an oxidative stress activates the production of toxins by F. graminearum. The involvement of Fgap1 in this activation was investigated. A deleted mutant and a strain expressing a truncated constitutive form of Fgap1 were constructed. None of the mutants was affected in pathogenicity. The deleted mutant showed higher level of trichothecenes production associated with overexpression of Tri genes. Moreover activation of toxin accumulation in response to oxidative stress was no longer observed. Regarding the mutant with the truncated constitutive form of Fgap1, toxin production was strongly reduced. Expression of oxidative stress response genes was not activated in the deleted mutant and expression of the gene encoding the mitochondrial superoxide dismutase MnSOD1 was up-regulated in the mutant with the truncated constitutive form of Fgap1. Our results demonstrate that Fgap1 plays a key role in the link between oxidative stress response and F. graminearum secondary metabolism.

Coupling of transcriptional response to oxidative stress and secondary metabolism regulation in filamentous fungi

To survive sudden and potentially lethal changes in their environment, filamentous fungi must sense and respond to a vast array of stresses, including oxidative stresses. The generation of reactive oxygen species, or ROS, is an inevitable aspect of existence under aerobic conditions. In addition, in the case of fungi with pathogenic lifestyles, ROS are produced by the infected hosts and serve as defense weapons via direct toxicity, as well as effectors in fungal cell death mechanisms. Filamentous fungi have thus developed complex and sophisticated responses to evade oxidative killing. Several steps are determinant in these responses, including the activation of transcriptional regulators involved in the control of the antioxidant machinery. Gathering and integrating the most recent advances in knowledge of oxidative stress responses in fungi are the main objectives of this review. Most of the knowledge coming from two models, the yeast Saccharomyces cerevisiae and fungi of the genus Aspergillus, is summarized. Nonetheless, recent information on various other fungi is delivered when available. Finally, special attention is given on the potential link between the functional interaction between oxidative stress and secondary metabolism that has been suggested in recent reports, including the production of mycotoxins.

Maize kernel antioxidants and their potential involvement in Fusarium ear rot resistance

The potential involvement of antioxidants (α-tocopherol, lutein, zeaxanthin, β-carotene, and ferulic acid) in the resistance of maize varieties to Fusarium ear rot was the focus of this study. These antioxidants were present in all maize kernel stages, indicating that the fumonisin-producing fungi (mainly Fusarium verticillioides and Fusarium proliferatum ) are likely to face them during ear colonization. The effect of these compounds on fumonisin biosynthesis was studied in F. verticillioides liquid cultures. In carotenoid-treated cultures, no inhibitory effect of fumonisin accumulation was observed while a potent inhibitory activity was obtained for sublethal doses of α-tocopherol (0.1 mM) and ferulic acid (1 mM). Using a set of genotypes with moderate to high susceptibility to Fusarium ear rot, ferulic acid was significantly lower in immature kernels of the very susceptible group. Such a relation was nonexistent for tocopherols and carotenoids. Also, ferulic acid in immature kernels ranged from 3 to 8.5 mg/g, i.e., at levels consistent with the in vitro inhibitory concentration. Overall, our data support the fact that ferulic acid may contribute to resistance to Fusarium ear rot and/or fumonisin accumulation.

Chlorogenic acid and maize ear rot resistance: a dynamic study investigating Fusarium graminearum development, deoxynivalenol production, and phenolic acid accumulation

Fusarium graminearum is the causal agent of Gibberella ear rot and produces trichothecene mycotoxins. Basic questions remain unanswered regarding the kernel stages associated with trichothecene biosynthesis and the kernel metabolites potentially involved in the regulation of trichothecene production in planta. In a two-year field study, F. graminearum growth, trichothecene accumulation, and phenolic acid composition were monitored in developing maize kernels of a susceptible and a moderately resistant variety using quantitative polymerase chain reaction and liquid chromatography coupled with photodiode array or mass spectrometry detection. Infection started as early as the blister stage and proceeded slowly until the dough stage. Then, a peak of trichothecene accumulation occurred and infection progressed exponentially until the final harvest time. Both F. graminearum growth and trichothecene production were drastically reduced in the moderately resistant variety. We found that chlorogenic acid is more abundant in the moderately resistant variety, with levels spiking in the earliest kernel stages induced by Fusarium infection. This is the first report that precisely describes the kernel stage associated with the initiation of trichothecene production and provides in planta evidence that chlorogenic acid may play a role in maize resistance to Gibberella ear rot and trichothecene accumulation.

The velvet gene, FgVe1, affects fungal development and positively regulates trichothecene biosynthesis and pathogenicity in Fusarium graminearum

Trichothecenes are a group of toxic secondary metabolites produced mainly by Fusarium graminearum (teleomorph: Gibberella zeae) during the infection of crop plants, including wheat, maize, barley, oats, rye and rice. Some fungal genes involved in trichothecene biosynthesis have been shown to encode regulatory proteins. However, the global regulation of toxin biosynthesis is still enigmatic. In addition to the production of secondary metabolites belonging to the trichothecene family, F. graminearum produces the red pigment aurofusarin. The gene regulation underlying the production of aurofusarin is not well understood. The velvet gene (veA) is conserved in various genera of filamentous fungi. Recently, the veA gene from Aspergillus nidulans has been shown to be the key component of the velvet complex regulating development and secondary metabolism. Using blast analyses, we identified the velvet gene from F. graminearum, FgVe1. Disruption of FgVe1 causes several phenotypic effects. However, the complementation of this mutant with the FgVe1 gene restores the wild-type phenotypes. The in vitro phenotypes include hyperbranching of the mycelium, suppression of aerial hyphae formation, reduced hydrophobicity of the mycelium and highly reduced sporulation. Our data also show that FgVe1 modulates the production of the aurofusarin pigment and is essential for the expression of Tri genes and the production of trichothecenes. Pathogenicity studies performed on flowering wheat plants indicate that FgVe1 is a positive regulator of virulence in F. graminearum.

The dent stage of maize kernels is the most conducive for fumonisin biosynthesis under field conditions

The fungal pathogen Fusarium verticillioides infects maize ears and produces fumonisins, known for their adverse effects on human and animal health. Basic questions remain unanswered regarding the kernel stage(s) associated with fumonisin biosynthesis and the kernel components involved in fumonisin regulation during F. verticillioides-maize interaction under field conditions. In this 2-year field study, the time course of F. verticillioides growth and fumonisin accumulation in developing maize kernels, along with the variations in kernel pH and amylopectin content, were monitored using relevant and accurate analytical tools. In all experiments, the most significant increase in fumonisin accumulation or in fumonisin productivity (i.e., fumonisin production per unit of fungus) was shown to occur within a very short period of time, between 22/32 and 42 days after inoculation and corresponding to the dent stage. This stage was also characterized by acidification in the kernel pH and a maximum level of amylopectin content. Our data clearly support published results based on in vitro experiments suggesting that the physiological stages of the maize kernel play a major role in regulating fumonisin production. Here we have validated this result for in planta and field conditions, and we demonstrate that under such conditions the dent stage is the most conducive for fumonisin accumulation.

Cinnamic-derived acids significantly affect Fusarium graminearum growth and in vitro synthesis of type B trichothecenes

The impact of five phenolic acids (ferulic, coumaric, caffeic, syringic, and p-hydroxybenzoic acids) on fungal growth and type B trichothecene production by four strains of Fusarium graminearum was investigated. All five phenolic acids inhibited growth but the degree of inhibition varied between strains. Our results suggested that the more lipophilic phenolic acids are, the higher is the effect they have on growth. Toxin accumulation in phenolic acid-supplemented liquid glucose, yeast extract, and peptone cultures was enhanced in the presence of ferulic and coumaric acids but was reduced in the presence of p-hydroxybenzoic acid. This modulation was shown to correlate with a regulation of TRI5 transcription. In this study, addition of phenolic acids with greater antioxidant properties resulted in a higher toxin accumulation, indicating that the modulation of toxin accumulation may be linked to the antioxidant properties of the phenolic acids. These data suggest that, in planta, different compositions in phenolic acids of kernels from various cultivars may reflect different degrees of sensitivity to "mycotoxinogenesis."

Exogenous H2O2and catalase treatments interfere withTrigenes expression in liquid cultures ofFusarium graminearum

Effect of exogenous H(2)O(2) and catalase was tested in liquid cultures of the deoxynivalenol and 15-acetyldeoxynivalenol-producing fungus Fusarium graminearum. Accordingly to previous results, H(2)O(2) supplementation of the culture medium leads to increased toxin production. This study indicates that this event seems to be linked to a general up regulation of genes involved in the deoxynivalenol and 15-acetyldeoxynivalenol biosynthesis pathway, commonly named Tri genes. In catalase-treated cultures, toxin accumulation is reduced, and Tri genes expression is significantly down regulated. Furthermore, kinetics of expression of several Tri genes is proposed in relation to toxin accumulation. Biological meanings of these findings are discussed.

Distribution of toxigenicFusariumspp. and mycotoxin production in milling fractions of durum wheat

A reliable and sensitive PCR assay to specifically detect trichothecene-producing Fusarium spp. in milling fractions and kernel tissue of naturally infected durum wheat is reported. Assays were based on a combination of primers derived from the trichodiene synthase and the beta-tubulin genes. The occurrence of toxigenic Fusarium spp. in semolina and wheat tissue (grain ends, crease, pericarp, aleurone layer, germ and albumen) was detected, even for a weakly contaminated wheat sample. Penetration of toxigenic Fusarium spp. into the interior of durum wheat kernel was demonstrated for the Nefer variety, indicating that none of the tissue structures within the wheat kernel acted as an effective barrier to fungal invasion. Moreover, after inoculation by toxigenic Fusarium strains, semolina was shown to allow high yields of trichothecenes, while bran was demonstrated to contain biochemical inhibitors able to significantly reduce trichothecene production. These results will be useful in improving breeding strategies to control trichothecene contamination of durum wheat kernels.

Accumulation of deoxynivalenol and its 15-acetylated form is significantly modulated by oxidative stress in liquid cultures of Fusarium graminearum

Liquid cultures of Fusarium graminearum were supplemented with H2O2 or other oxidative compounds. The accumulation kinetics of the resulting trichothecenes were monitored. At non-lethal concentrations, the H2O2 treatments modulated toxin accumulation, dependent on the method of supplementation. When H2O2 was added at the same time as the inoculation, higher levels of toxins accumulated 30 days later. Conversely, adding H2O2 2 or 7 days after inoculation had little effect. When H2O2 was added daily over the course of the culture, the accumulation of trichothecenes was rapidly and strongly enhanced. The fungus may adapt to oxidative stress when the first exposure to H2O2 occurs at the beginning of the culture course. The highest toxin levels were measured when the H2O2 was added daily. The importance of the first hours of culture was confirmed: pre-treating conidia with H2O2 does not affect their germination kinetics but leads to a reduction in the yield of trichothecenes 40 days later. The H2O2 regulation of this trichothecene accumulation may be specific, as paraquat, another pro-oxidant compound, inhibits their production. Since H2O2 is a major component of the oxidative burst occurring in pathogen/host interactions, these data support the theory that trichothecenes may act as virulence factors.

Post-transcriptional regulation in Xenopus embryos: role and targets of EDEN-BP

EDEN (embryo deadenylation element)-dependent deadenylation is a regulatory process that was initially identified in Xenopus laevis early embryos and was subsequently shown to exist in Drosophila oocytes. Recent data showed that this regulatory process is required for somitic segmentation in Xenopus. Inactivation of EDEN-BP (EDEN-binding protein) causes severe segmentation defects, and the expression of segmentation markers in the Notch signalling pathway is disrupted. We showed that the mRNA encoding XSu(H) (Xenopus suppressor of hairless), a protein central to the Notch pathway, is regulated by EDEN-BP. Our data also indicate that other segmentation RNAs are targets for EDEN-BP. To identify new EDEN-BP targets, a microarray analysis has been undertaken.

Ancestral origins of the prion protein gene D178N mutation in the Basque Country

Fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD) are familial prion diseases with autosomal dominant inheritance of the D178N mutation. FFI has been reported in at least 27 pedigrees around the world. Twelve apparently unrelated FFI and fCJD pedigrees with the characteristic D178N mutation have been reported in the Prion Diseases Registry of the Basque Country since 1993. The high incidence of familial prion diseases in this region may reflect a unique ancestral origin of the chromosome carrying this mutation. In order to investigate this putative founder effect, we developed "happy typing", a new approach to the happy mapping method, which consists of the physical isolation of large haploid genomic DNA fragments and their analysis by the Polymerase Chain Reaction in order to perform haplotypic analysis instead of pedigree analysis. Six novel microsatellite markers, located in a 150-kb genomic segment flanking the PRNP gene were characterized for typing haploid DNA fragments of 285 kb in size. A common haplotype was found in patients from the Basque region, strongly suggesting a founder effect. We propose that "happy typing" constitutes an efficient method for determining disease-associated haplotypes, since the analysis of a single affected individual per pedigree should provide sufficient evidence.

Characterization of the genomic organization of the region bordering the centromere of chromosome V of Podospora anserina by direct sequencing

A Podospora anserina BAC library of 4800 clones has been constructed in the vector pBHYG allowing direct selection in fungi. Screening of the BAC collection for centromeric sequences of chromosome V allowed the recovery of clones localized on either sides of the centromere, but no BAC clone was found to contain the centromere. Seven BAC clones containing 322,195 and 156,244bp from either sides of the centromeric region were sequenced and annotated. One 5S rRNA gene, 5 tRNA genes, and 163 putative coding sequences (CDS) were identified. Among these, only six CDS seem specific to P. anserina. The gene density in the centromeric region is approximately one gene every 2.8kb. Extrapolation of this gene density to the whole genome of P. anserina suggests that the genome contains about 11,000 genes. Synteny analyses between P. anserina and Neurospora crassa show that co-linearity extends at the most to a few genes, suggesting rapid genome rearrangements between these two species.

A rapid and efficient method using chromoslots to assign any newly cloned DNA sequence to its cognate chromosome in the filamentous fungus Podospora anserina

An efficient method was developed to assign cloned genes to individual chromosomes of the fungus Podospora anserina. The chromosomes were separated by pulsed-field gel electrophoresis and the DNA was isolated from the gel bands. The DNA from the isolated chromosomes was slotted onto membranes; the resulting chromoslots were used to confirm that genetically mapped genes could be detected in the expected position. Then, 20 genes, not yet assigned to a linkage group, were attributed to individual chromosomes while six were attributed to a band containing two chromosomes.

HET-E and HET-D belong to a new subfamily of WD40 proteins involved in vegetative incompatibility specificity in the fungus Podospora anserina

Vegetative incompatibility, which is very common in filamentous fungi, prevents a viable heterokaryotic cell from being formed by the fusion of filaments from two different wild-type strains. Such incompatibility is always the consequence of at least one genetic difference in specific genes (het genes). In Podospora anserina, alleles of the het-e and het-d loci control heterokaryon viability through genetic interactions with alleles of the unlinked het-c locus. The het-d2(Y) gene was isolated and shown to have strong similarity with the previously described het-e1(A) gene. Like the HET-E protein, the HET-D putative protein displayed a GTP-binding domain and seemed to require a minimal number of 11 WD40 repeats to be active in incompatibility. Apart from incompatibility specificity, no other function could be identified by disrupting the het-d gene. Sequence comparison of different het-e alleles suggested that het-e specificity is determined by the sequence of the WD40 repeat domain. In particular, the amino acids present on the upper face of the predicted beta-propeller structure defined by this domain may confer the incompatible interaction specificity.

Altered antibody repertoires of plasma IgM and IgG toward nonself antigens in patients with warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is characterized by an accelerated extravascular clearance of red blood cells (RBC) mediated by RBC-bound IgG autoantibodies. We have recently demonstrated significantly altered self-reactive antibody (Ab) repertoires of plasma IgM in WAIHA patients. The natural IgM Ab repertoire in plasma is critical in modulating both autoimmune and alloimmune responses. In the present study, we investigated IgM and IgG Ab repertoires of WAIHA patients toward nonself antigens (Ag) using a quantitative immunoblotting technique, followed by multiparametric statistical analysis of the data. We demonstrate significantly altered Ab repertoires of IgM and IgG toward nonself Ag in WAIHA patients. The reactivity of plasma IgM of WAIHA patients was reduced compared to that of healthy individuals, independent of administering an immunosuppressive therapy. We observed that an increase in reactivity of plasma IgM during clinical remission of the disease was associated with the development of allo-Ab toward RBC-antigens during RBC transfusions. Taken together, the data indicate altered Ab repertoires of plasma IgM and IgG toward nonself Ag in WAIHA patients. A broadly reduced reactivity of plasma IgM toward nonself Ag might influence the adaptive immune response in WAIHA patients.

Defects in components of the proteasome enhance transcriptional silencing at fission yeast centromeres and impair chromosome segregation

Fission yeast centromeres are transcriptionally silent and form a heterochromatin-like structure essential for normal centromere function; this appears analogous to heterochromatin and position effect variegation in other eukaryotes. Conditional mutations in three genes designated cep (centromere enhancer of position effect) were found to enhance transcriptional silencing within centromeres. Cloning of the cep1(+) and cep2(+) genes by functional complementation revealed that they are identical to the previously described genes pad1(+) and mts2(+), respectively, which both encode subunits of the proteasome 19S cap. Like Mts2 and Mts4, epitope-tagged Cep1/Pad1 localizes to or near the nuclear envelope throughout the cell cycle. The cep mutants display a range of phenotypes depending on the temperature. Silencing within the central domain of centromeres is increased at 36 degrees C. This suggests that the proteasome is involved in regulating silencing and thus centromeric chromatin architecture, possibly by lowering the level of some chromatin-associated protein by ubiquitin-dependent degradation. This is the first report of defective proteasome function affecting heterochromatin-mediated transcriptional silencing. At 36 and 32 degrees C, the cep mutants lose chromosomes at an elevated rate, and at 18 degrees C, the mutants are cryosensitive for growth. Cytological analysis at 18 degrees C revealed a defect in sister chromatid separation while other mitotic events occurred normally, indicating that cep mutations might interfere specifically with the degradation of inhibitor(s) of sister chromatid separation. These observations suggest that 19S subunits confer a level of substrate specificity on the proteasome and raise the possibility of a link between components involved in centromere architecture and sister chromatid cohesion.

Identification of surface molecules on salivary glands of the mosquito, Aedes aegypti, by a panel of monoclonal antibodies

Malaria transmission by the mosquito vector requires sporozoite invasion into mosquito salivary glands. Parasites probably enter the glands by specific receptor-ligand interactions with molecules on the surface of the glands. We have undertaken the characterization of salivary gland surface molecules of Aedes aegypti to identify candidate receptors for Plasmodium gallinaceum sporozoite invasion. Monoclonal antibodies (mAbs) were generated against antigen enriched for salivary gland membranes and basal lamina. A panel of 44 mAbs were generated that bound to surface molecules of mosquito tissues. Twenty-four mAbs bound exclusively to salivary glands, six bound to salivary glands and ovaries, one bound to salivary gland and midgut, and 13 bound to all tissues tested. We present data on the immunolocalization and biochemical characteristics of the antigens. Many of the salivary gland-specific mAbs bound preferentially to the median and distal lateral lobes of the salivary glands, indicating that there are anatomical region-specific biochemical differences on the gland surface. These lobes of the salivary glands are the preferential sites of malaria sporozoite invasion. Therefore, antigens specific for these regions are promising candidate receptors for sporozoite invasion. The present identification of surface molecules of mosquito salivary glands by means of monoclonal antibodies represents the first description of individual molecules on the mosquito salivary gland surface. This work lays the basis for further studies on the molecular mechanisms involved in malaria sporozoite invasion of mosquito salivary glands.

Lactobacillus species identification, H2O2 production, and antibiotic resistance and correlation with human clinical status

Lactobacilli recovered from the blood, cerebrospinal fluid, respiratory tract, and gut of 20 hospitalized immunocompromised septic patients were analyzed. Biochemical carbohydrate fermentation and total soluble cell protein profiles were used to identify the species. Hydrogen peroxide production was measured. Susceptibility to 19 antibiotics was tested by a diffusion method, and the MICs of benzylpenicillin, amoxicillin, imipenem, erythromycin, vancomycin, gentamicin, and levofloxacin were determined. A small number of species produced H2O2, and antibiotic susceptibilities were species related. Eighteen (90%) of the isolates were L. rhamnosus, one was L. paracasei subsp. paracasei, and one was L. crispatus. L. rhamnosus, L. paracasei subsp. paracasei isolates, and the type strains were neither H2O2 producers nor vancomycin susceptible (MICs, >/=256 microgram/ml). L. crispatus, as well as most of the type strains of lactobacilli which belong to the L. acidophilus group, was an H2O2 producer and vancomycin susceptible (MICs, <4 microgram/ml).

Regulation of gene expression during the vegetative incompatibility reaction in Podospora anserina. Characterization of three induced genes

Vegetative incompatibility in fungi limits the formation of viable heterokaryons. It results from the coexpression of incompatible genes in the heterokaryotic cells and leads to a cell death reaction. In Podospora anserina, a modification of gene expression takes place during this reaction, including a strong decrease of total RNA synthesis and the appearance of a new set of proteins. Using in vitro translation of mRNA and separation of protein products by two-dimensional gel electrophoresis, we have shown that the mRNA content of cells is qualitatively modified during the progress of the incompatibility reaction. Thus, gene expression during vegetative incompatibility is regulated, at least in part, by variation of the mRNA content of specific genes. A subtractive cDNA library enriched in sequences preferentially expressed during incompatibility was constructed. This library was used to identify genomic loci corresponding to genes whose mRNA is induced during incompatibility. Three such genes were characterized and named idi genes for genes induced during incompatibility. Their expression profiles suggest that they may be involved in different steps of the incompatibility reaction. The putative IDI proteins encoded by these genes are small proteins with signal peptides. IDI-2 protein is a cysteine-rich protein. IDI-2 and IDI-3 proteins display some similarity in a tryptophan-rich region.

Use of a linear plasmid containing telomeres as an efficient vector for direct cloning in the filamentous fungus Podospora anserina

In Podospora anserina a linear plasmid with telomeric ends behaves as an artificial acentric minichromosome. Transformation is at least 100 times more efficient than with integrative vectors. Genomic DNA was inserted in this plasmid in vitro and the mixture used to transform a leu1-1 strain. Many fungal clones containing the leu1 gene as a genomic insert in the linear plasmid were identified. The leu1 gene was rescued as a circular plasmid in Escherichia coli demonstrating that a direct cloning procedure can be applied for the fungus P. anserina. The conservation of telomeric sequences among filamentous fungi suggests that a telomere-based linear plasmid could provide a general cloning vector for filamentous fungi.

The mod-A suppressor of nonallelic heterokaryon incompatibility in Podospora anserina encodes a proline-rich polypeptide involved in female organ formation

Vegetative incompatibility in fungi results from the control of heterokaryon formation by the genes present at het loci. Coexpression of antagonistic het genes in the same hyphae leads to a lethal process. In Podospora anserina, self-incompatible strains containing nonallelic incompatible genes in the same nucleus are inviable as the result of a growth arrest and a lytic process. Mutations in suppressor genes (mod genes) can restore the viability. These mod mutations also interfere with developmental processes, which suggests common steps between the incompatibility reaction and cellular differentiation. The mod-A locus, responsible for growth arrest in the self-incompatible strains, is also involved in the control of the development of female organs. The mod-A gene was isolated. An open reading frame 687 amino acids long was identified. The MOD-A-encoded polypeptide is rich in proline residues, which are clustered in a domain containing a motif that displays similarity to SH3-binding motifs, which are known to be involved in protein-protein interactions. Construction of a strain deleted for mod-A confirmed that the product of this gene involved in differentiation is a key regulator of growth arrest associated with vegetative incompatibility.

Identification of Rhodococcus, Gordona and Dietzia species using carbon source utilization tests ("Biotype-100" strips)

The "Biotype-100" identification system (BioMérieux, La Balme-Ies-Grottes, France) based on carbon source utilization was evaluated for its ability to discriminate among 10 species of Rhodococcus, 7 species of Gordona and one species of Dietzia. The type strains of three species of Tsukamurella and 8 species of Nocardia were also included in the study. Results were compared with chemotaxonomic and conventional data. Carbon source utilization was shown to be reliable, rapid and easy to use when compared with standard identification methods. The 29 species tested were unambiguously separated by carbon source utilization tests. Rhodococcus equi was found to be heterogenous.

Analysis of antibody reactivities toward self antigens of IgM of patients with Waldenström's macroglobulinemia

By using a quantitative immunoblotting technique, we have analyzed the repertoires of antibody reactivities of IgM directed toward self antigens in the serum of patients with Waldenström's macroglobulinemia (WM) and in the serum of healthy adults. Monoclonal IgM of patients with WM expressed various degrees of polyreactivity and a high degree of heterogeneity with regard to the number and the nature of the protein bands that were recognized in homologous tissue extracts. Heterogeneous patterns of reactivity of WM IgM contrasted with the conserved profiles of reactivity of IgM in the serum of healthy blood donors. Protein bands that were recognized by WM IgM belonged to the restricted set of self antigens recognized in homologous tissues by normal polyclonal IgM, indicating the absence of a disease-specific reactivity profile of monoclonal WM IgM. Thus, monoclonal IgM that is present in large amounts in WM distorts the homogeneous pattern of reactivity of natural antibodies with self antigens which characterizes the natural antibody repertoire of healthy individuals.

Venereal and vertical transmission of the Aedes albopictus parvovirus in Aedes aegypti mosquitoes

Following per oral infection of Aedes aegypti larvae with Aedes albopictus parvovirus (AaPV), infected males and females adults were tested for their ability to transmit the virus venereally and vertically, respectively. Both types of transmission were observed. A low percentage (2.2%) of AaPV-free females were found contaminated by the virus after mating with AaPV-infected males. Although no significant difference was observed in the fecundity of orally infected and virus-free females, 17.1% of infected ones died before egg laying, whereas no mortality occurred during the same period in virus-free females. There was a clear relationship between the virus titer in the orally infected females and both mortality and infection in their offspring. The virus titer averaged 10(6.2) 50% tissue culture infective doses (TCID50s) in F1 females and 10(3.3) TCID50 in F1 females. Nevertheless, AaPV did not persist in an experimentally infected population of mosquitoes beyond the second generation.

The repertoire of serum IgM in normal mice is largely independent of external antigenic contact

Antigen-free (AGF) and germ-free (GF) mice, although essentially free of serum IgG, maintain normal levels of circulating IgM. Using a quantitative immunoblot assay, we have now analyzed the repertoire of serum IgM from AGF, GF, and specific pathogen-free (SPF) BALB/c mice, on large panels of natural antigens from homologous tissues and bacteria. The reactivity profiles were very similar in the three groups of mice. Multiparametric statistic evaluation of the data showed that BALB/c animals, SPF, GF, and AGF mice constitute an homogeneous group with similar immunoreactivity profiles when compared to C57BL/6. Differences between immunoreactivity profiles of GF and AGF mice were observed, but were not statistically significant. These results suggest that the serum IgM repertoire of normal mice is strictly regulated and selected by endogenous ligands.

Pathogenicity of the Aedes albopictus parvovirus (AaPV), a denso-like virus, for Aedes aegypti mosquitoes

AaPV, a denso-like virus isolated from a C6/36 clone of the Aedes albopictus cell line, proved to be very pathogenic for Aedes aegypti first and third instar larvae following per os infection. The mortality reached 90% in 10 days for larvae infected at the first instar. Several factors, such as temperature, larval density and stage, and duration of contact with infectious particles, influenced infection. The virus titer in females surviving infection at the third larval instar reached 10(8) TCID50. Adult mosquitoes were sensitive to virus inoculation and to cytotransfection by viral DNA. Histological and ultrastructural studies revealed the presence of dense nuclei in almost all of the larval tissues with the exception of the midgut.

Identification of Turicella otitidis isolated from a patient with otorrhea associated with surgery: differentiation from Corynebacterium afermentans and Corynebacterium auris

Turicella otitidis is a newly described coryneform bacterium isolated from middle ear fluids. We report here on the diagnosis of a strain isolated from otorrhea. The API Coryne system (bioMérieux, Marcy I'Etoile, France) used alone failed to differentiate T. otitidis, Corynebacterium afermentans, and Corynebacterium auris (ANF group). Biochemical tests such as DNase, enzymatic reactions (API ZYM; bioMérieux), and carbon substrate assimilation tests (Biotype 100; bioMérieux) allow presumptive identification. However, only chemotaxonomy and molecular biology can achieve unequivocal differentiation among these three species.

The self-reactive antibody repertoire of normal human serum IgM is acquired in early childhood and remains conserved throughout life

The authors have used a quantitative immunoblotting technique to analyse the antibody repertoire of IgM in cord blood and in the serum of young children, young adult males and aged males directed towards antigens in homologous tissues utilized as sources of self antigens. The reactivities of IgM with self antigens exhibited striking homogeneity and invariance among newborns. Self-reactive IgM repertoires of children, young adults and aged males were markedly conserved among individuals and comprised most of the anti-self reactivities that prevailed in neonates. Reactivities of IgM with bacterial antigens showed a high degree of homogeneity among newborns but were more diverse in children, young adults and elderly individuals. Diversity of IgM reactivities with self and non-self antigens did not vary significantly with aging. Principal component analysis (PCA) and linear discriminant analysis (LDA) of the data discriminated between self-reactive IgM repertoires of newborns and children, but failed to discriminate between repertoires of children, young adults and aged males. The data indicate that the self-reactive antibody repertoire of IgM differentiates during the first years of life and remains relatively constant thereafter.

PCR methods for identification and specific detection of probiotic lactic acid bacteria

Probiotics are defined as "microbes improving animal feed." Three lactic acid bacteria, previously selected as probiotic for pig feeding, were identified by sequencing the variable V1 region of the 16S rDNA after PCR amplification primed in the flanking constant region. A VR region showing strong nucleotide differences between the three probiotic and the reference strains was delimited. Oligonucleotides specific for each strain were designed. A specific assay for probiotic detection was developed, based on a PCR reaction with three primers.

Plasmodium: a quantitative molecular assay for detection of sporogonic-stage malaria parasites

We present a molecular assay to detect malaria parasites during sporogonic development in the mosquito host. Specific primers for Plasmodium-specific small-subunit ribosomal RNA sequences not present in mosquito RNA were used in a reverse transcriptase-polymerase chain reaction (RT-PCR) assay. A synthetic RNA quantitative competitor was made which included targets for two primers and a target sequence for a hybridization probe which is also present in the natural parasite ribosome. The heterobifunctional Tth polymerase was used to carry out both reverse transcription and DNA-dependent polymerase chain reaction in a single reaction tube. Ookinetes and sporozoites, the stages from the beginning and end of sporogonic development, respectively, were both recognized in the assay. The assay was calibrated for quantitation of sporozoites by making a standard curve with counted sporozoites. The linear range of the calibrated assay allowed accurate quantitation of parasite number over at least two orders of magnitude, from 10 to 1000 sporozoites, in each RT-PCR reaction.

Plasmodium gallinaceum: sporozoite invasion of Aedes aegypti salivary glands is inhibited by anti-gland antibodies and by lectins

There is evidence which suggests that malaria sporozoites recognize mosquito salivary glands by specific receptor-ligand interactions. We are interested in identifying the putative salivary gland receptor(s) for sporozoite invasion. We used an in vivo bioassay for sporozoite invasion of salivary glands. In this assay, purified sporozoites from mature oocytes of Plasmodium gallinaceum were injected into Aedes aegypti mosquitoes and salivary glands were dissected at different time points after injection. One half of the maximum invasion of salivary glands by sporozoites occurred by 6 hr, and salivary gland sporozoite load did not increase further after 24 hr postinjection. This assay was used to determine the effect of experimental treatments with antibodies and lectins at 24 hr postinjection. We raised a rabbit polyclonal antiserum against female Ae. aegypti salivary glands which recognized tissue-specific determinants in the basal lamina of salivary glands. Purified IgG antibody fraction of the immune serum blocked sporozoite invasion in vivo. We tested a panel of 19 lectins and found 7 which bound to salivary glands. Of these 7, succinylated wheat germ agglutinin and wheat germ agglutinin completely blocked sporozoite invasion; Pisum sativum agglutinin and soybean agglutinin partially blocked; and concanavalin A, Dolichos biflorus agglutinin, and Phaseolus vulgaris erythroagglutinin did not block. Our results suggest that sporozoites interact with glycosylated salivary gland surface molecules which serve as receptors for invasion, and which may be in the salivary gland basal lamina. Because the putative sporozoite receptors contain immunogenic determinants, it is feasible to identify them by an immunological strategy.

Analysis of the normal human IgG antibody repertoire. Evidence that IgG autoantibodies of healthy adults recognize a limited and conserved set of protein antigens in homologous tissues

We have used a quantitative immunoblot technique to analyze the Ab repertoire of IgG in the serum of healthy adults with a large panel of homologous and foreign Ags in tissue extracts. Densitometric patterns of reactivity of purified IgG with self-Ags exhibited striking homogeneity among individuals with regard to the protein bands that were recognized. Purified IgG showed higher levels of reactivity with self-Ags than IgG in whole serum. Reactivity with self-Ags of IgG in whole serum was restricted to a small number of protein bands (fewer than 10). There were significant inter-individual differences in the intensity and nature of immunoreactivities. Purified IgG of different individuals exhibited heterogeneous patterns of immunoreactivity with Ags in bacterial extracts. Comparative analysis of repertoires of IgG and IgM indicated that all protein Ags recognized by IgM were also reactive with purified IgG. Some proteins in homologous and in foreign tissue extracts reacted solely with IgG. Our observations provide direct evidence for the restricted and conserved character of the antiself-repertoire of IgG of healthy adults and suggest that natural IgG Ab repertoires in serum are specifically selected for reactivity with a limited set of self-Ags. In addition, IgG autoreactivity in whole serum is controlled by non-IgG factors that determine the unique reactivity pattern of each individual.

Analysis of the normal human IgG antibody repertoire. Evidence that IgG autoantibodies of healthy adults recognize a limited and conserved set of protein antigens in homologous tissues

We have used a quantitative immunoblot technique to analyze the Ab repertoire of IgG in the serum of healthy adults with a large panel of homologous and foreign Ags in tissue extracts. Densitometric patterns of reactivity of purified IgG with self-Ags exhibited striking homogeneity among individuals with regard to the protein bands that were recognized. Purified IgG showed higher levels of reactivity with self-Ags than IgG in whole serum. Reactivity with self-Ags of IgG in whole serum was restricted to a small number of protein bands (fewer than 10). There were significant inter-individual differences in the intensity and nature of immunoreactivities. Purified IgG of different individuals exhibited heterogeneous patterns of immunoreactivity with Ags in bacterial extracts. Comparative analysis of repertoires of IgG and IgM indicated that all protein Ags recognized by IgM were also reactive with purified IgG. Some proteins in homologous and in foreign tissue extracts reacted solely with IgG. Our observations provide direct evidence for the restricted and conserved character of the antiself-repertoire of IgG of healthy adults and suggest that natural IgG Ab repertoires in serum are specifically selected for reactivity with a limited set of self-Ags. In addition, IgG autoreactivity in whole serum is controlled by non-IgG factors that determine the unique reactivity pattern of each individual.

Invariance and restriction toward a limited set of self-antigens characterize neonatal IgM antibody repertoires and prevail in autoreactive repertoires of healthy adults

Analysis of the reactivity of IgM with self-antigens in tissues by a quantitative immunoblotting technique showed striking invariance among newborns in the human and in the mouse. The self-reactive repertoire of IgM of adults was also markedly conserved; it comprised most anti-self reactivities that prevailed among neonates. Multivariate analysis confirmed the homogeneity of IgM repertoires of neonates toward self- and non-self-antigens. Multivariate analysis discriminated between newborn and adult repertoires for reactivity with two of five sources of self-proteins and with non-self-antigens. Our observations support the concept that naturally activated B lymphocytes are selected early in development and throughout life for reactivity with a restricted set of self-antigens.