Isolation and genetic study of Aspergillus nidulans mutants defective in pyrimidine biosynthesis]

8 uridine-requiring pyr mutants were isolated from Aspergillus nidulans under nitrosoguanidine treatment. All the mutants are capable to grow on the medium containing 20 mkg/ml of uridine or cytidine, or 100 mkg/ml of uracil, and they do not utilize thymidine, thymine, cytosine and deoxyuridine. Their ability to grow in the presence of orotic acid demonstrates that the pyrimidine synthesis in all the mutants is blocked at stages preceding the conversion of orotic acid into orotidine monophosphate. All the pyr mutants are of nuclear nature, they are recessive and represent three complementation groups located in the VIII chromosome. Unlike U. maydis mutant, the requirement in pyrimidines does not increase the sensitivity of A. nidulans pyr mutants to UV-irradiation.     

Phenotypes of double conidiation mutants of Aspergillus nidulans.

A series of strains, doubly mutant at conidiation loci, have been made. The phenotypes of these strains reflected the epistasy of earlier blocking mutants over later ones and confirmed the order of gene sequence predicted from the phenotypes of single mutants. Oligosporogenous mutants gave complex interactions, especially between brl and med mutants. These results indicated that (i) gene action overlapped in time, (ii) several parts of the conidial apparatus were interchangeable and (iii) nuclei leaving the vesicle were not irreversibly programmed. Structures produced by mutants were reminiscent of the conidial apparatus of other Aspergillus species and of related genera.     

蓝光促进黑曲霉分生孢子发育和产糖化酶的研究

以黑暗为对照 ,研究了不同光质对黑曲霉产糖化酶及生长发育的影响。持续蓝光作用下 ,孢子萌发后菌丝较粗 ,菌丝细胞顶端膨大显著 ,菌丝细胞膜的通透性增加 ,残糖消耗快 ,孢子和孢子穗增大。在 3(4d时 ,蓝光下菌丝产糖化酶活力最高达 6 6 0 (30U mL ,比黑暗高出了 15. 4 % ,生物量增加了 4 9. 4 8% ,菌丝细胞可溶性蛋白含量提高了10 0. 5 6 % ,尤其是在开始产孢子的阶段 ,蓝光下黑曲霉产糖化酶活力、生物量有很大提高。研究表明 ,蓝光明显促进黑曲霉分生孢子发育和产孢阶段包括糖化酶在内的多种淀粉酶活力的迅速增加。     

Aspergillus niger mutants with increased glucose oxidase production

Summary Aspergillus niger NRRL-3, an organism used for the industrial scale production of d-gluconic acid and glucose oxidase (EC 1.1.3.4), was subjected to mutagenesis and selection for acid production on diagnostic media containing methyl red. The plates contained 0.1 M d-glucose, a concentration that does not produce a color change in the medium surrounding mycelia of the parental strain under the conditions employed. Mutagenized spores yielded occasional colonies which were able to grow rapidly and were surrounded by a reddish zone. A number of such presumptive mutants were selected and isolated. Twenty-six such strains were grown in shaken cultures with liquid media containing 0.01, 0.1 or 0.5 M d-glucose, harvested, disrupted and the specific activity of d-glucose oxidase determined. Seven of the mutant strains had glucose oxidase specific activities markedly higher than the parental strain.Paper No. 8393, Nebraska Agricultural Research Division.     

Isolation and physical characterization of three essential conidiation genes from Aspergillus nidulans

We cloned and characterized three genes from Aspergillus nidulans, designated brlA, abaA and wetA, whose activities are required to complete different stages of conidiophore development. Inactivation of these genes causes major abnormalities in conidiophore morphology and prevents expression of many unrelated, developmentally regulated genes, without affecting expression of nonregulated genes. The three genes code for poly(A)⁺RNAs that begin to accumulate at different times during conidiation. The brlA-and abaA-encoded RNAs accumulate specifically in cells of the conidiophore. The wetA-encoded RNA accumulates in mature conidia. Inactivation of the brlA gene prevents expression of the abaA and wetA genes, whereas inactivation of the abaA gene prevents expression of the wetA gene. Our results confirm genetic predictions as to the temporal and spatial patterns of expression of these genes and demonstrate that these patterns are specified at the level of RNA accumulation.     

Isolation and characterization of the Aspergillus niger trpC gene

The Aspergillus niger trpC gene was isolated by complementation experiments with an Escherichia coli trpC mutant. Plasmid DNA containing the A. niger trpC gene transforms an Aspergillus nidulans mutant strain, defective in all three enzymatic activities of the trpC gene, to Trp+, indicating the presence of a complete and functional trpC gene. Southern blot analysis of DNA from these Trp+ transformants showed that plasmid DNA was present but that this DNA was not integrated at the site of the chromosomal trpC locus. The A. niger trpC gene was localized on the cloned fragment by heterologous hybridization experiments and sequence analysis. These experiments suggest that the organization of the A. niger trpC gene is identical to that of the analogous A. nidulans trpC and the Neurospora crassa trp-1 genes.     

A phosphoglucose isomerase mutant in Aspergillus nidulans is defective in hyphal polarity and conidiation

Upon germination Aspergillus nidulans swoM1 exhibits abnormal development by extending a primary germ tube that quickly reverts to isotropic growth and results in an enlarged, swollen apex with pronounced wall thickenings. Apical lysis occurs in 38% of the germlings. A point mutation in the AN6037.3 gene encoding the only phosphoglucose isomerase in A. nidulans is responsible for the defect. Loss of polarity is bypassed when glucose is replaced with alternate carbon sources but in all cases the mutant is unable to conidiate due to a block in conidiophore development at vesicle formation. In conidiophores SwoM::GFP localizes to multiple punctate, foci within each actively growing cell type, and to multiple foci in mature dormant conidia. In hyphae SwoM::GFP localized to two rings spanning the center of mature septa. In hyphae localization is concentrated at actively growing hyphal tips.     

Identification of growth phenotypes in Aspergillus niger pectinase over-producing mutants using image analysis procedures

Relative growth rates of four strains of Aspergillus niger were estimated by image analysis of colonies grown with mineral salts and 10 g pectin/l. Water activity (aw) levels were 0.96 and 0.99 and 2-deoxy-D-glucose (2DG) was added up to 0.1 g/l. These techniques proved useful to select mould strains for pectinase production in culture media with different water activities. © Rapid Science Ltd. 1998