Rosemary E. Bradshaw

Bio: Rosemary E. Bradshaw is an academic researcher from University of Nottingham. The author has contributed to research in topics: Parasexual cycle & Aspergillus nidulans. The author has an hindex of 4, co-authored 6 publications receiving 198 citations.

Aspects of Genetic Interaction in Hybrids of Aspergillus nidulans and Aspergillus rugulosus obtained by Protoplast Fusion

Abstract: Summary: Hybrids were produced by protoplast fusion between strains of Aspergillus rugulosus and mitotic master strains of Aspergillus nidulans with a genetic marker on each linkage group. Analysis of segregants induced by growth on benomyl revealed recombination between every pair of unlinked markers. Parental combinations of markers were often recovered at significantly higher frequencies than expected. This aberrant segregation was not correlated with any particular pair of linkage-groups and was attributed to inter-species incompatibility. The segregation of genetic markers of A. rugulosus from the hybrids suggested that A. nidulans and A. rugulosus may differ in haploid chromosome number and chromosome size. In sexual crosses between A. nidulans and strains containing chromosomes of mixed parental origin recombinants were recovered. The results support the classification of A. nidulans and A. rugulosus as separate species.

Parasexual Analysis of Aspergillus parasiticus

Abstract: SUMMARY: Ten genetic markers were located on six linkage groups in Aspergillus parasiticus by means of the parasexual cycle. Diploids, selected by complementation of spore colour and auxotrophic markers, were subjected to induced haploidization by treatment with benlate. Haploid segregants, including recombinants resulting from mitotic crossing over, were distinguished from diploids by their stability and growth in the presence of benlate. Evidence is presented for the linkage of two genetic markers, norA and verA, which affect the biosynthesis of aflatoxin.

Genetic analysis in Aspergillus rugulosus using the parasexual cycle

Abstract: Auxotrophic and conidial colour mutants were induced in a strain of A. rugulosus by u.v.-irradiation and used to produce a preliminary genetic map by means of the parasexual cycle. Seven diploids with different combinations of eight genetic markers were isolated and segregants were obtained by haploidization on benlate. Analysis of genetic marker segregation amongst the progeny revealed linkage between only one pair of markers, thus indicating the presence of at least seven linkage groups in A. rugulosus .

Enzymes in Food Processing

Abstract: G. Reed, Introduction. K.L. Parkin, General Characteristics of Enzymes. K.L. Parkin, Environmental Effects in Enzyme Activity. J Wegstein, Modern Methods of Enzyme Expression and Design. P. Aldercreutz, Immobilization. R. Bigelis, Carbohydrates. J. Adler-Nissen, Proteases. S.E. Godtfredsen, Lipases and Esterases. F. Hammer, Oxidoreductoses. T. Szakucki, Application of Oxidoreductases. B. Sproessler, Milling and Baking. R.E. Hebeda, Starches, Sugars, And Syrup. R.J. Brown, Dairy Products. W. Pilmik, Pectic Enzymes in Fruit and Vegetable Juice Manufacture. T. Nagodawithana, Flavor Enhancers. J.-C. Villettaz, Wine. J. Power, Beer. D. Bernnachi, Enzymes for Meat Tenderization. G. Stafansson, Fish Processing.

Comparative mapping of aflatoxin pathway gene clusters in Aspergillus parasiticus and Aspergillus flavus.

Abstract: Aflatoxins are toxic and carcinogenic secondary metabolites produced by the fungi Aspergillus flavus and A. parasiticus. Aflatoxins are synthesized by condensation of acetate units; their synthesis is estimated to involve at least 16 different enzymes. In this study we have shown that at least nine genes involved in the aflatoxin biosynthetic pathway are located within a 60-kb DNA fragment. Four of these genes, nor-1, aflR, ver-1, and omtA (previously named omt-1), have been cloned in A. flavus and A. parasiticus. In addition, five other genes, pksA, uvm8, aad, ord-1, and ord-2 have been recently cloned in A. parasiticus. The pksA, aad, and uvm8 genes exhibit sequence homologies to polyketide synthase, aryl-alcohol dehydrogenase, and fatty acid synthase genes, respectively. The cDNA sequences of ord-1 and ord-2 genes, which may be involved in later steps of aflatoxin biosynthesis, have been determined; the ord-1 gene product exhibits homology to cytochrome P-450-type enzymes. By characterizing the overlapping regions of the DNA inserts in different cosmid and lambda DNA clones, we have determined the order of these aflatoxin pathway genes within this 60-kb DNA region to be pksA, nor-1, uvm8, aflR, aad, ver-1, ord-1, ord-2, and omtA in A. parasiticus and nor-1, aflR, ver-1, ord-1, ord-2, and omtA in A. flavus. The order is related to the order in enzymatic steps required for aflatoxin biosynthesis. The physical distances (in kilobase pairs) and the directions of transcription of these genes have been determined for both aflatoxigenic species.

The production of organic acids.

Abstract: The production of organic acids covers two aspects: first, the metabolic pathways involved in the biosynthesis, and, second, the industrial process strategy adopted The review seeks to show the underlying biochemical similarities in the biosynthesis of organic acids and the resulting similarities in the commercial processes Two groups of acids are defined, those with a "long" biosynthetic path from glucose, involving much of the glycolytic pathway and the tricarboxylic acid cycle, and those acids with a "short pathway", essentially a biotransformation of glucose The regulation of the pathways and the future developments in metabolic control theory and genetic manipulations relating to them are considered The organisms used industrially are also limited, Aspergillus sp and Candida yeasts; again the underlying metabolic similarities lead to similar strategies for all the acids discussed

Isolation and characterization of a gene from Aspergillus parasiticus associated with the conversion of versicolorin A to sterigmatocystin in aflatoxin biosynthesis.

Abstract: DNA isolated from the wild-type aflatoxin-producing (Afl+) fungus Aspergillus parasiticus NRRL 5862 was used to construct a cosmid genomic DNA library employing the homologous gene (pyrG) encoding orotidine monophosphate decarboxylase for selection of fungal transformants. The cosmid library was transformed into an Afl- mutant, A. parasiticus CS10 (ver-1 wh-1 pyrG), deficient in the conversion of the aflatoxin biosynthetic intermediate versicolorin A to sterigmatocystin. One pyrG+ Afl+ transformant was identified. DNA fragments from this transformant, recovered by marker rescue, contained part of the cosmid vector including the pyrG gene, the ampr gene, and a piece of the original genomic insert DNA. Transformation of these rescued DNA fragments into A. parasiticus CS10 resulted in production of wild-type levels of aflatoxin and abundant formation of sclerotia. The gene responsible for this complementation (ver-1) was identified by Northern RNA analysis and transformation with subcloned DNA fragments. The approximate locations of transcription initiation and polyadenylation sites of ver-1 were determined by an RNase protection assay and cDNA sequence analysis. The predicted amino acid sequence, deduced from the ver-1 genomic and cDNA nucleotide sequences, was compared with the EMBL and GenBank data bases. The search revealed striking similarity with Streptomyces ketoreductases involved in polyketide biosynthesis. Images

Physical and transcriptional map of an aflatoxin gene cluster in Aspergillus parasiticus and functional disruption of a gene involved early in the aflatoxin pathway.

Abstract: Two genes involved in aflatoxin B1 (AFB1) biosynthesis in Aspergillus parasiticus, nor-1 and ver-1, were localized to a 35-kb region on one A. parasiticus chromosome and to the genomic DNA fragment carried on a single cosmid, NorA. A physical and transcriptional map of the 35-kb genomic DNA insert in cosmid NorA was prepared to help determine whether other genes located in the nor-1-ver-1 region were involved in aflatoxin synthesis. Northern (RNA) analysis performed on RNA isolated from A. parasiticus SU1 grown in aflatoxin-inducing medium localized 14 RNA transcripts encoded by this region. Eight of these transcripts, previously unidentified, showed a pattern of accumulation similar to that of nor-1 and ver-1, suggesting possible involvement in AFB1 synthesis. To directly test this hypothesis, gene-1, encoding one of the eight transcripts, was disrupted in A. parasiticus CS10, which accumulates the aflatoxin precursor versicolorin A, by insertion of plasmid pAPNVES4. Thin-layer chromatography revealed that gene-1 disruptant clones no longer accumulated versicolorin A. Southern hybridization analysis of these clones indicated that gene-1 had been disrupted by insertion of the disruption vector. These data confirmed that gene-1 is directly involved in AFB1 synthesis. The predicted amino acid sequence of two regions of gene-1 showed a high degree of identity and similarity with the beta-ketoacyl-synthase and acyltransferase functional domains of polyketide synthases, consistent with a proposed role for gene-1 in polyketide backbone synthesis.