Septum formation in Aspergillus nidulans

Filamentous fungi form multicellular hyphae that are partitioned by septa. In A. nidulans, septum formation requires the assembly of a septal band following the completion of mitosis. Recent observations show that this band is a dynamic structure composed of actin, a septin and a formin. In addition, assembly is dependent upon a conserved protein kinase cascade that regulates mitotic exit and septation in yeast. Hyphal differentiation may reflect the regulation of this cascade by cyclin-dependent kinase activity. In this review, the dynamics and regulation underlying the assembly of the septal band are discussed.     

Complementation among developmental mutants in Aspergillus nidulans

Summary In heterokaryons between pairs of aconidial mutants of Aspergillus nidulans one of the component strains usually shows a striking prevalance in the contribution to the conidial crop. By assuming that the prevailing strain is blocked earlier and the succumbent one later in the process of differentiation, a series of mutations can be arranged in a consistent order.Some mutant strains do not fit the scheme exactly but show a general tendency to be succumbent to early mutants and prevalent over the late ones. A criterion for arraying genes involved in differentiation according to the order of their physiological action is proposed.     

Growth-mediated metabolic activation of promutagens in Aspergillus nidulans

7 procarcinogens belonging to different chemical classes (nitrosamines, hydrazoalkanes, oxazaphosphorines and aromatic amines) were tested in A. nidulans for the induction of point mutations with two genetic systems (8-AG resistance and induction of methionine suppressors).

Dimethylnitrosamine, diethylnitrosamine, nitrosomorpoline, dimethyl-hydrazine, procarbazine and cyclophosphamide gave positive results with a good dose—effect relationship in the growth-mediated assay, whereas they gave negative or borderline positive results in the plate incorporation assay. 2-Aminoanthracene was completely negative with both experimental procedures.

DMN, DEN and NM were also tested for their ability to induce somatic segregation: all were positive when assayed in the growth-mediated assay.     

构巢曲霉冻干菌粉的制备及优化

【背景】目前,用以降解园林绿化废弃物中木质素的菌剂多为液体菌剂或固体菌剂,鲜有对粉状菌剂的研究。【目的】研制高活性冻干菌粉,提高其冻干存活率并优化其工艺,以解决液体菌剂或固体菌剂在运输、储藏及使用上存在的问题。【方法】以一株木质素降解菌构巢曲霉(Aspergillus nidulans)为研究对象,利用真空冷冻干燥法制备冻干菌粉。以菌株的冻干存活率为评价指标,通过单因素试验筛选适于菌株冻干过程的保护剂种类及浓度梯度,再通过正交试验优化冻干菌粉复合保护剂配方。获得配方后,进一步探究冻干菌粉的复水条件和储藏条件。【结果】保护效果较优的4种保护剂成分经复配后对冻干存活率的影响顺序为蔗糖>葡萄糖>脱脂乳粉> α-乳糖。经优化后的保护剂配方以蔗糖15%、葡萄糖1%、α-乳糖10%、脱脂乳粉1%为最佳;复水条件以生理盐水为溶剂,复水30 min为最优。在此条件下制备和使用冻干菌粉,菌株的冻干存活率可达83.33%,有效活菌数可达1.2×10¹⁰ CFU/g。最佳储藏温度为-20 ℃,在此温度下保存28 d后,菌粉活性无明显下降。【结论】该研究获得的制备和储藏构巢曲霉冻干菌粉条件,具有菌株损失率低、可长时间保存的特点,对推进木质素降解菌在实际生产中应用具有积极作用。     

Analysis of Two Aspergillus nidulans Genes Encoding Extracellular Proteases

vanKuyk, P. A., Cheetham, B. F., and Katz, M. E. 2000. Analysis of two Aspergillus nidulans genes encoding extracellular proteases. Characterization of prtAΔ mutants, generated by gene disruption, showed that the prtA gene is responsible for the majority of extracellular protease activity secreted by Aspergillus nidulans at both neutral and acid pH. The prtAΔ mutation was used to map the prtA gene to chromosome V. Though aspartic protease activity has never been reported in A. nidulans and the prtAΔ mutants appear to lack detectable acid protease activity, a gene (prtB) encoding a putative aspartic protease was isolated from this species. Comparison of the deduced amino acid sequence of PrtB to the sequence of other aspergillopepsins suggests that the putative prtB gene product contains an eight-amino-acid deletion prior to the second active site Asp residue of the protease. RT-PCR experiments showed that the prtB gene is expressed, albeit at a low level.     

Cytochrome-c reductases from wild-type and mutant strains of Aspergillus nidulans

Summary The sedimentation coefficients of the NADPH: cytochrome-c oxidoreductase enzymes from wild-type and mutant strains of Aspergillus nidulans have been estimated by sucrose density gradient centrifugation. In the wild-type, two species of cytochrome-c reductase were found, with sedimentation coefficients of 13.7s and 7.6s respectively. The 13.7s species did not appear to be associated with the enzymes of nitrate reduction, whereas the 7.6s species was closely associated with NADPH: nitrate oxidoreductase. In mutant strains lacking nitrate reductase, a thir species of cytochrome-c reductase with a sedimentation coefficient of 4.5s was found. There is some evidence that this 4.5s cytochrome-c reductase is a subunit or breakdown product of nitrate reductase and a model is presented for the role of this 4.5s cytocnorome-c reductase in the assembly of the intact nitrate reductase molecule.     

Cloning and characterisation of the cytochrome c gene of Aspergillus nidulans

The cytochrome c gene (cycA) of the filamentous fungus Aspergillus nidulans has been isolated and sequenced. The gene is present in a single copy per haploid genome and encodes a polypeptide of 112 amino acid residues. The nucleotide sequence of the A. nidulans cycA gene shows 87% identity to the DNA sequence of the Neurospora crassa cytochrome c gene, and approximately 72% identity to the sequence of the Saccharomyces cerevisiae iso-1-cytochrome c gene (CYC1). The S. cerevisiae CYC1 gene was used as a heterologous probe to isolate the homologous gene in A. nidulans. The A. nidulans cytochrome c sequence contains two small introns. One of these is highly conserved in terms of position, but the other has not been reported in any of the cytochrome c genes so far sequenced. Expression of the cycA gene is not affected by glucose repression, but has been shown to be induced approximatly tenfold in the presence of oxygen and three- to fourfold under heatshock conditions.     

Two new genes involved in signalling ambient pH in Aspergillus nidulans

Two new genes, palH and palI, where mutations mimic the effects of acidic growth pH have been identified in Aspergillus nidulans. A palH mutation is phenotypically indistinguishable from mutations in the palA, palB, palC, and palF genes, whereas palI mutations differ only in that they allow some growth at pH 8. Mutations in palA, B, C, F, and H are epistatic to a palI mutation and the significance of this epistasis is discussed. Additionally, palE and palB mutations have been shown to be allelic. Thus, a total of six genes where mutations mimic acidic growth conditions has been identified.     

Mutants of Aspergillus nidulans altered in the transport of methylammonium and ammonium

Summary Mutations to methylammonium resistance occur in at least two loci in Aspergillus nidulans, meaA in linkage group IV and meaB in linkage group III. Transport studies using methylammonium-¹⁴C, at a concentration which inhibits protein synthesis in the wild type but not in resistant mutants, show that meaA mutants are defective in methylammonium (and hence ammonium) transport. The ability of meaA mutations to be expressed in the absence of a substrate of the ammonium-methylammonium transport system suggests that ammonium efflux may be involved, although it has not been established whether ammonium influx is also affected.     

Studies of partially repressed mutants at the tamA and areA loci in Aspergillus nidulans

Summary Mutants, designated tamA ^r, have been isolated on the basis of simultaneous resistance to toxic analogues thiourea, aspartate hydroxamate and chlorate with L-alanine as the sole nitrogen source. tamA ^r mutants are also resistant to methylammonium. This resistance of tamA ^r mutants is correlated with partially repressed activity of a number of enzyme and transport systems regulated by ammonium. Furthermore, tamA ^r mutants have low NADP-glutamate dehydrogenase (NADP-GDH) activity and also efflux ammonium under certain growth conditions.Mutants at the areA locus (areA ^r) have also been isolated on the basis of resistance to these analogues, with nitrate or L-aspartate as the nitrogen source. These, similar to tamA ^r lesions, result in resistance to methylammonium and are partially repressed for ammonium repressible systems, but in contrast to tamA ^r, areA ^r alleles have wild-type NADP-GDH activity and normal ammonium efflux. tamA ^r and areA ^r mutants grow as wild type on all nitrogen or carbon sources tested, are recessive, and appear to be epistatic to all other mutations (gdhA1, meaA8 and meaB6) which result in derepressed levels of ammonium regulated system. Whereas tamA ^r and areA ^r phenotypes are additive, tamA ^r is epistatic to areA ^d phenotype.