Genetic diversity in Aspergillus parasiticus population from the peanut agroecosystem in Argentina

AIMS: The aims of this work were to identify potential sources of Aspergillus parasiticus inoculum and to evaluate the sclerotial and toxigenic profiles of this species from the peanut agroecosystem in Argentina. Likewise, the genetic diversity of A. parasiticus population was analysed using vegetative compatibility group (VCG) analysis. METHODS AND RESULTS: The A. parasiticus strains were isolated from soil, debris and peanut seeds in Córdoba Province, Argentina. A. parasiticus was recovered from the three sources analysed. Only 11 of 185 A. parasiticus isolates (5.9%) did not produce aflatoxins, while 57% produced sclerotia. Twenty-four VCG were identified from 63 isolates. The VCG diversity index for A. parasiticus, expressed as the number of groups divided by the total number of isolates, was 0.31. In general, there were significant differences among VCG in aflatoxin production. CONCLUSIONS: The presence of aflatoxigenic strains of A. parasiticus in the three substrates suggests that they may be an important source of aflatoxin in Argentina's peanut agroecosystem. The A. parasiticus population shows a low genetic diversity. SIGNIFICANCE AND IMPACT OF THE STUDY: The present study showed data on inoculum distribution, aflatoxin and sclerotia production and genetic diversity in an A. parasiticus population isolated from the peanut agroecosystem in Argentina.     

H(2)O(2) generation in Saccharomyces cerevisiae respiratory pet mutants: effect of cytochrome c

Impaired electron transport chain function has been related to increases in reactive oxygen species (ROS) generation. Here we analyzed different pet mutants of Saccharomyces cerevisiae in order to determine the relative contribution of respiratory chain components in ROS generation and removal. We found that the maintenance of respiration strongly prevented mitochondrial H(2)O(2) release and increased cellular H(2)O(2) removal. Among all respiratory-deficient strains analyzed, cells lacking cytochrome c (cyc3 point mutants) presented the highest level of H(2)O(2) synthesis, indicating that the absence of functional cytochrome c in mitochondria leads to oxidative stress. This finding was supported by the presence of high levels of catalase and peroxidase activity despite the lack of respiration. Furthermore, the addition of exogenous cytochrome c to isolated yeast mitoplasts significantly reduced H(2)O(2) detection in a manner enhanced by cytochrome c reduction and the presence of a functional respiratory chain. Together, our results indicate that the maintenance of electron transport by cytochrome c prevents ROS generation by the respiratory chain.     

Fermentation of cashew apple juice to produce high added value products

The use of agriculture substrates in industrial biotechnological processes has been increasing because of its low cost. Cashew apples are considered an agriculture low cost product in the Brazilian Northeast because the cashew cultivation is done mainly to produce cashew nuts. About 90% of the cashew apples production is lost in the field after removing the nut. In this work, the use of clarified cashew apple juice as substrate for microbial cultivation was investigated. The results showed that cashew apple juice is a good source of reducing sugars and can be used to grow Leuconostoc mesenteroides to produce high added value products such as dextran, lactic acid, mannitol and oligosaccharides.     

Identification of transcription elements in the 5' intergenic region shared by LON and MDJ1 heat shock genes from the human pathogen Paracoccidioides brasiliensis. Evaluation of gene expression

The MDJ1/LON locus is conserved among pathogenic dimorphic fungi. We have mapped using DNase I footprinting and mobility shift assays three putative heat shock elements and one AP-1 binding domain (ARE) in the 5' intergenic region shared by PbMDJ1and PbLON (ML) from Paracoccidioides brasiliensis. The region bearing an ARE-like towards PbLON also has an opposite skn-1-like element. We studied genetically and pathogenically distinct isolates Pb18 and Pb3, where ML is polymorphic and the number of elements detected was higher. The functionality of the elements was suggested by the stimulatory response of both genes to heat shock and oxidative stress. Co-regulation occurred upon heat shock from 36 to 42 degrees C and, only in Pb3, also during mycelium to yeast transformation (26-36 degrees C). In Pb18, PbMDJ1 seemed to be preferentially expressed in yeast. Our study might help understand regulation of genes involved in fungal adaptation to the host.     

Muscle delta13C change in Nile tilapia (Oreochromis niloticus) fingerlings fed on C3-or C4-cycle plants grain-based diets

The effects of grain-based diets from C3 or C4-cycle plants on muscle delta(13)C change process in Nile tilapia (Oreochromis niloticus) fingerlings were investigated. Two groups of sex reversal males Nile tilapia fingerlings were fed with isoproteic (32.0% DP) and isocaloric (3200 kcal DE/kg) diets, differing from each other by their delta(13)C. Muscle samples were collected and the carbon isotopic composition was measured. For C4 diet, the formula for the muscle delta(13)C change related to the intake time of a new diet was delta(13)C=-14.88-9.21e(-0.0209t) and the half-life (T) of the muscle carbon was 33.2 days. For C3 diet, the formula was delta(13)C=-25.43+8.59e(-0.0533t) with T=13 days. The C3 diet was considered more appropriate based on its palatability and consequent larger food intake than the C4 diet, resulting in an increased muscle delta(13)C change rate. However, for future studies, would be necessary to mix both the C3 and C4 feedstuffs to formulate diets nutritionally appropriated, with contrasting stable isotopes signatures. Tissue delta(13)C change rate is therefore indicated as a promising tool to better understand the biotic and abiotic factors that influence nutrients utilization from the diet and animal growth.     

Expression of LH receptor mRNA splice variants in bovine granulosa cells: changes with follicle size and regulation by FSH in vitro

In cattle, most evidence suggests that granulosa cells express LH receptors (LHR) after (or as) the follicle becomes dominant, however there is some suggestion that granulosa cells from smaller pre-dominant follicles may express several LHR mRNA splice variants. The objective of this study was to measure LHR expression in bovine follicles of defined size and steroidogenic ability, and in granulosa cells from small follicles (<6 mm diameter) undergoing differentiation in vitro. Semiquantitative RT-PCR demonstrated that LHR mRNA was undetectable in granulosa cells of follicles <7 mm diameter (nondominant follicles), and increased with follicle diameter in follicles >7 mm diameter. Splice variants with deletions of exon 10 and part of exon 11 were detected as previously described, and we detected a novel splice variant with a deletion of exon 3. Cultured granulosa cells contained LHR mRNA, but with significantly greater amounts of variants with deletions of exon 10 and/or exon 11 compared with cells from dominant follicles. FSH increased the abundance of some but not all LHR mRNA splice variants in cultured granulosa cells. The addition of LH to cultured cells did not increase progesterone secretion, despite the presence of LHR mRNA. Collectively, these data suggest that granulosa cells do not acquire functional LHR until follicle dominance occurs.     

Interaction of Bacillus thuringiensis svar. israelensis Cry toxins with binding sites from Aedes aegypti (Diptera: Culicidae) larvae midgut

This work shows in vitro processing of Bacillus thuringiensis svar. isralensis Cry toxins and the capacity of the active fragments to bind the midgut microvilli of Aedes aegypti larvae. Processing of Cry11Aa, Cry4Aa and Cry4Ba yielded double fragments of 38-30, 45-20 and 45-18 kDa, respectively. Competition assays showed that all active (125)I-Cry toxins are able to specifically bind to brush border membrane fractions and they might share a common class of binding sites. The values of IC(50) suggested that toxins do not display high affinity for the receptors from brush border membrane fractions, while dissociation assays showed that binding was irreversible, indicating the insertion of toxins in the cell membrane.     

Development of a SCAR marker for the analysis of B chromosome presence in Partamona helleri (Hymenoptera, Apidae)

Chromosomes in hymenopteran insects cannot currently be analysed in adult individuals. The only available cytogenetic techniques need to be performed in larvae. Here we develop and implement a SCAR (Sequence Characterized Amplified Region) marker, associated with B chromosomes in the bee Partamona helleri, which has proven to be very useful to reveal B chromosome presence in adults from natural populations. The marker was tested in ten different colonies simultaneously analysed by both molecular (ten adults per colony) and cytogenetic (20 larvae per colony) techniques. The presence of the SCAR marker always showed the same pattern as B chromosome presence: both were present or absent in all individuals from a same colony, or both were present in only part of the individuals from a same colony. This molecular marker is thus a useful tool for analysing new aspects of this B chromosome system such as B frequency and geographical distribution, B transmission, or B effects in adult individuals.