Adenine auxotrophic mutants of Aspergillus oryzae: development of a novel transformation system with triple auxotrophic hosts

adeA and adeB genes homologous to Saccharomyces cerevisiae ADE1 and ADE2, respectively, were cloned from Aspergillus oryzae. AdeA and AdeB share 62.8% and 52.5% identities with S. cerevisiae Ade1 and Ade2, respectively. In order to obtain triple auxotrophic mutants from A. oryzae, 12 red-colored mutant colonies were isolated by UV mutagenesis of a double auxotrophic host, NS4 (niaD(-), sC(-)), as a parent strain. All the mutants exhibited adenine auxotrophy and showed fluorescence in the vacuoles due to accumulation of a purine biosynthetic pathway precursor. Adenine auxotrophy of all the mutants was restored by introduction of either A. oryzae adeA or adeB genes. Sequence analysis demonstrated that substitutions or deletions of a single base pair occurred, inducing substitutions or frame shifts of amino acid sequences in both ade genes complementing the mutants. This study provides a novel host-vector system with triple auxotrophy in A. oryzae.     

Adenine Auxotrophic Mutants of Aspergillus oryzae: Development of a Novel Transformation System with Triple Auxotrophic Hosts

adeA and adeB genes homologous to Saccharomyces cerevisiae ADE1 and ADE2, respectively, were cloned from Aspergillus oryzae. AdeA and AdeB share 62.8% and 52.5% identities with S. cerevisiae Ade1 and Ade2, respectively. In order to obtain triple auxotrophic mutants from A. oryzae, 12 red-colored mutant colonies were isolated by UV mutagenesis of a double auxotrophic host, NS4 (niaD ^?, sC ^?), as a parent strain. All the mutants exhibited adenine auxotrophy and showed fluorescence in the vacuoles due to accumulation of a purine biosynthetic pathway precursor. Adenine auxotrophy of all the mutants was restored by introduction of either A. oryzae adeA or adeB genes. Sequence analysis demonstrated that substitutions or deletions of a single base pair occurred, inducing substitutions or frame shifts of amino acid sequences in both ade genes complementing the mutants. This study provides a novel host-vector system with triple auxotrophy in A. oryzae.     

Developmental defects resulting from arginine auxotrophy in Aspergillus nidulans

A mutant of Aspergillus nidulans, isolated for inability to form asexual spores (conidia) on complete medium, was found to regain the ability to conidiate if the medium was supplemented with arginine. On minimal medium the mutant required arginine for growth but at a much lower concentration than that required for conidiation. This mutant, designated argB12, thus defines a phase-critical gene, i.e. a gene whose function is in greater demand for development than for growth. In addition to its aconidial phenotype, the mutant also exhibited (depending on the medium) aberrant sexual development and a low efficiency of conidial germination. In crosses, each of these developmental phenotypes segregated with arginine auxotrophy. Genetic and biochemical analyses showed the argB12 mutation to be an allele of the previously described argB locus, mutants of which lack ornithine transcarbamylase. Arginine-requiring mutants at at least two other loci were also found to be defective in asexual sporulation, but the germination defect appears to be specific to argB mutants.     

Targeted gene disruption by homologous recombination in the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1

In contrast to the high accumulation in sequence data for hyperthermophilic archaea, methodology for genetically manipulating these strains is still at an early stage. This study aimed to develop a gene disruption system for the hyperthermophilic euryarchaeon Thermococcus kodakaraensis KOD1. Uracil-auxotrophic mutants with mutations in the orotidine-5'-monophosphate decarboxylase gene (pyrF) were isolated by positive selection using 5-fluoroorotic acid (5-FOA) and used as hosts for further transformation experiments. We then attempted targeted disruption of the trpE locus in the host strain by homologous recombination, as disruption of trpE was expected to result in tryptophan auxotrophy, an easily detectable phenotype. A disruption vector harboring the pyrF marker within trpE was constructed for double-crossover recombination. The host cells were transformed with the exogenous DNA using the CaCl(2) method, and several transformants could be selected based on genetic complementation. Genotypic and phenotypic analyses of a transformant revealed the unique occurrence of targeted disruption, as well as a phenotypic change of auxotrophy from uracil to tryptophan caused by integration of the wild-type pyrF into the host chromosome at trpE. As with the circular plasmid, gene disruption with linear DNA was also possible when the homologous regions were relatively long. Shortening these regions led to predominant recombination between the pyrF marker in the exogenous DNA and the mutated allele on the host chromosome. In contrast, we could not obtain trpE disruptants by insertional inactivation using a vector designed for single-crossover recombination. The gene targeting system developed in this study provides a long-needed tool in the research on hyperthermophilic archaea and will open the way to a systematic, genetic approach for the elucidation of unknown gene function in these organisms.     

Transformation of a mycoparasitic Trichoderma harzianum strain with the argB gene of Aspergillus nidulans

A transformation system was developed for the mycoparasitic filamentous fungus Trichoderma harzianum, based upon complementation of auxotrophic mutants. Prototrophic transformants were obtained using plasmids pSal23 and pAN5-41B, carrying the Aspergillus nidulans argB gene, and both the Aspergillus nidulans argB and Escherichia coli lacZ genes, respectively.     

Total biosynthesis of diterpene aphidicolin, a specific inhibitor of DNA polymerase α: heterologous expression of four biosynthetic genes in Aspergillus oryzae

Clustering of biosynthetic genes for producing fungal secondary metabolites, which frequently consist of less than ten genes, has been recognized with numerous genomes. The heterologous expression of whole genes in the clusters will therefore produce various types of natural products when using a suitable fungal host. We introduced the whole gene cluster for the biosynthesis of diterpene aphidicolin into the fungal quadruple auxotrophic host, Aspergillus oryzae, by using four different vectors (pTAex3, pPTRI, pUSA and pAdeA) which harbor a starch-inducible promoter/terminator to examine the expression conditions. The resulting quadruple transformant carrying the genes of geranylgeranyl diphosphate synthase PbGGS, terpene synthase PbACS, and two monooxygenases (PbP450-1 and PbP450-2) produced aphidicolin. The double and triple transformants also respectively produced aphidicolan-16β-ol and 3-deoxyaphidicolin. Alternative host Saccharomyces cerevisiae carrying the genes, PbGGS and PbACS, produced key intermediate aphidicolan-16β-ol. This is the first example of a total biosynthesis of terpenoids using fungal hosts.     

Contribution Ratios of amyA, amyB, amyC Genes to High-Level α-Amylase Expression in Aspergillus oryzae

Aspergillus oryzae strains express α-amylases abundantly, and the genome reference strain RIB40 has three α-amylase genes (amyA, amyB, and amyC). However, there is no information on the contribution ratios of individual α-amylase genes to total expression. In this study, we generated single, double, and triple disruptants of α-amylase genes by employing a strain (ΔligD) with high gene-targeting efficiency and pyrG marker recycling in A. oryzae. All the disruptants showed reduced activities of α-amylases, and the triple disruptant completely lost activity. Comparative analyses of the activities and mRNA amounts of the α-amylases suggest that the contribution of amyA to the α-amylase expression is smaller than those of amyB and amyC. The present study suggests that the ability to express a large amount of α-amylases in A. oryzae is attributed to gene duplication of genes such as amyB and amyC.     

Isolation and symbiotic characterization of transposon Tn5-induced arginine auxotrophs of Sinorhizobium meliloti

Seventeen arginine auxotrophic mutants of Sinorhizobium meliloti Rmd201 were isolated by random transposon Tn5 mutagenesis using Tn5 delivery vector pGS9. Based on intermediate feeding studies, these mutants were designated as argA/argB/argC/argD/argE (ornithine auxotrophs), argF/argI, argG and argH mutants. The ornithine auxotrophs induced ineffective nodules whereas all other arginine auxotrophs induced fully effective nodules on alfalfa plants. In comparison to the parental strain induced nodule, only a few nodule cells infected with rhizobia were seen in the nitrogen fixation zone of the nodule induced by the ornithine auxotroph. TEM studies showed that the bacteroids in the nitrogen fixation zone of ornithine auxotroph induced nodule were mostly spherical or oval unlike the elongated bacteroids in the nitrogen fixation zone of the parental strain induced nodule. These results indicate that ornithine or an intermediate of ornithine biosynthesis, or a chemical factor derived from one of these compounds is required for the normal development of nitrogen fixation zone and transformation of rhizobial bacteria into bacteroids during symbiosis of S. meliloti with alfalfa plants.     

Arginine Auxotrophic Phenotype of Mutations in pyrA of Salmonella typhimurium: Role of N-Acetylornithine in the Maturation of Mutant Carbamylphosphate Synthetase

Mutations in pyrA that abolish catalytic activity of carbamylphosphate synthetase cause auxotrophy for both arginine and a pyrimidine. Eight pyrA mutants auxotrophic only for arginine (AUX) were isolated by the mutagenized phage technique; three of these required arginine only at low temperature (20 degrees C). Explanations of the AUX phenotype based on bradytrophy were eliminated by the discovery that blocking the utilization of carbamylphosphate for pyrimidine biosynthesis by insertion of an additional mutation in pyrB (encoding aspartic transcarbamylase) did not reduce the requirement for arginine. In contrast, mutational blocks in the arginine biosynthetic pathway before N-acetylornithine (argB, argC, argG, or argH) did suppress the mutation in pyrA. This suggests that exogenous arginine permits growth of the AUX mutants by inhibiting the first step in the arginine pathway, thereby preventing accumulation of an intermediate that antagonizes mutant pyrA function. A mutation in argA (N-acetylornithinase) failed to suppress AUX, indicating that N-acetylornithine was the inhibitory intermediate. This intermediate had no effect on the catalytic or regulatory properties of carbamylphosphate synthetase from mutant cells grown under permissive conditions (37 degrees C). However, the regulatory properties of carbamylphosphate synthetase synthesized under restrictive conditions (20 degrees C) were demonstrably defective (insensitive to activation by ornithine); the enzyme synthesized under permissive conditions was activated by ornithine. A strain carrying an additional mutation (argC), which prevents the accumulation of N-acetylornithine, produced an ornithine-activatable enzyme at both growth temperatures. These results suggest that N-acetylornithine antagonizes the proper preconditioning or maturation of the mutant carbamylphosphate synthetase.     

Mutation of an arginine biosynthesis gene causes reduced pathogenicity in Fusarium oxysporum f. sp. melonis

Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for pathogenicity of Fusarium oxysporum f. sp. melonis. Of the 1,129 REMI transformants tested, 13 showed reduced pathogenicity on susceptible melon cultivars. One of the mutants, FMMP95-1, was an arginine auxotroph. Structural analysis of the tagged site in FMMP95-1 identified a gene, designated ARG1, which possibly encodes argininosuccinate lyase, catalyzing the last step for arginine biosynthesis. Complementation of FMMP95-1 with the ARG1 gene caused a recovery in pathogenicity, indicating that arginine auxotrophic mutation causes reduced pathogenicity in this pathogen.     

Pigment and virulence deficiencies associated with mutations in the aroE gene of Xanthomonas oryzae pv. oryzae

Xanthomonadins are yellow, membrane-bound pigments produced by members of the genus Xanthomonas. We identified an ethyl methanesulfonate-induced Xanthomonas oryzae pv. oryzae mutant (BXO65) that is deficient for xanthomonadin production and virulence on rice, as well as auxotrophic for aromatic amino acids (Pig(-) Vir(-) Aro(-)). Reversion analysis indicated that these multiple phenotypes are due to a single mutation. A genomic library of the wild-type strain was used to isolate a 7.0-kb clone that complements BXO65. By transposon mutagenesis, marker exchange, sequence analysis, and subcloning, the complementing activity was localized to a 849-bp open reading frame (ORF). This ORF is homologous to the aroE gene, which encodes shikimate dehydrogenase in various bacterial species. Shikimate dehydrogenase activity was present in the wild-type strain and the mutant with the complementing clone, whereas no activity was found in BXO65. This clone also complemented an Escherichia coli aroE mutant for prototrophy, indicating that aroE is functionally conserved in X. oryzae pv. oryzae and E. coli. The nucleotide sequence of the 2.9-kb region containing aroE revealed that a putative DNA helicase gene is located adjacent to aroE. Our results indicate that aroE is required for normal levels of virulence and xanthomonadin production in X. oryzae pv. oryzae.     

Cloning of the ATP sulphurylase gene of Schizosaccharomyces pombe by functional complementation

The ATP sulphurylase gene of Schizosaccharomyces pombe has been cloned by complementation of cysteine auxotrophy of a selenate-resistant mutant, which supposedly had a defect in ATP sulphurylase. A sulphate nonutilizing (cysteine auxotrophic) and selenate-resistant mutant of S. pombe was transformed with a wild-type S. pombe genomic library and sulphate-utilizing clones were isolated. The open reading frame encoding the ATP sulphurylase enzyme was found to be responsible for the restoration of sulphate assimilation. Transformants became as sensitive for selenate as the wild-type strain and produced a comparable amount of ATP sulphurylase as the prototrophic strains. The cloned ATP sulphurylase gene (sua1) proved to be an efficient selection marker in an ARS vector, when different isogenic or nonisogenic S. pombe selenate-resistant mutants were used as cloning hosts. Complementation of sua1- mutations by sua1-bearing multicopy vectors functions as a useful dual positive and negative selection marker. The cloned sua1 gene also complemented the met3 (ATP sulphurylase deficient) mutation in Saccharomyces cerevisiae.     

Mutagenesis of Protoplasts and Regeneration of Mycelium in the Mushroom Volvariella volvacea

Regenerating protoplasts were obtained from mycelial culture of the mushroom Volvariella volvacea by the action of the lytic enzyme Novozym 234 in the presence of 0.01 M phosphate buffer (pH 6.0) containing 0.6 M NaCl. Regeneration was found to be poor in liquid medium, but more than 50% regeneration was achieved on solid 2% agar medium overlaid with 0.5% agar. Protoplasts of V. volvacea were found to be highly sensitive to the killing action of both UV irradiation and N-methyl-N′-nitro-N-nitrosoguanidine. However, no morphological or auxotrophic mutants could be obtained from protoplasts by chemical mutagenesis. Four types of morphological mutants and one auxotrophic (adenine-negative) mutant were obtained from UV-irradiated protoplasts. The adenine-negative mutant of V. volvacea was found to be stable, not losing auxotrophy on repeated subculture.     

The importance of surface charge and hydrophobicity for the flocculation of chain-forming brewing yeast strains and resistance of these parameters to acid washing

Abstract This paper describes transformation of intact conidia of Aspergillus nidulans , auxotrophic for arginine, by using the biolistic process. The plasmid employed was pFB39, carrying the argB gene. The transformation frequency obtained was 81 transformants/ μg of DNA. Classical genetics and molecular analysis were conducted to analyse transformants and to determine in which chromosome integration took place.     

Multiple gene disruptions by marker recycling with highly efficient gene-targeting background (ΔligD) in Aspergillus oryzae

Previously we reported that double disruption of the proteinase genes (tppA and pepE) improved heterologous protein production by Aspergillus oryzae (Jin et al. Appl Microbiol Biotechnol 76:1059-1068, 2007). Since A. oryzae has 134 protease genes, the number of auxotrophy in a single host is limited for multiple disruptions of many protease genes. In order to rapidly perform multiple gene disruptions in A. oryzae, we generated the marker recycling system in highly efficient gene-targeting background. A. oryzae ligD gene homologous to Neurospora crassa mus-53 gene involved in nonhomologous chromosomal integration was disrupted, followed by disruption of the pyrG gene for uridine/uracil auxotroph. We further performed successive rounds of gene disruption (tppA and pepE) by the pyrG marker with high gene-targeting efficiency allowed by the DeltaligD background. After each disruption process the pyrG marker was excised by the direct repeats consisting of ~300 bp upstream flanking region of the target gene, resulting in no residual ectopic/foreign DNA fragments in the genome. Consequently, we succeeded to breed the double proteinase gene disruptant (DeltatppA DeltapepE) applicable to further sequential gene disruptions in A. oryzae.     

GUS为负标记的稻瘟病菌目标基因替换突变体双筛选体系

目标基因替换是基因功能研究的重要方法, 在生物工程领域广泛应用。为了提高真菌目标基因替换的效率, 以稻瘟病菌为研究对象, 建立了一种以gusA基因为负筛选标记的目标基因替换突变体双筛选体系(GUS-DS)。首先, 检测了78个真菌菌株的内源GUS活性, 发现除3个菌株外均呈阴性。同时, 将gusA基因导入稻瘟病菌、镰刀病菌、炭疽病菌后, 转化子可获得高的GUS活性。表明gusA可用作真菌中的筛选标记。然后, 以gusA为负标记, HPH为正标记, 以过氧化物酶体定位信号受体基因MGPEX5与MGPEX7的替换为例, 建立稻瘟病菌GUS-DS体系。对潮霉素抗性筛选获得的转化子通过GUS活性检测进一步筛选, 呈阴性者为可能突变体。通过PCR与Southern杂交对可能突变体进行验证, 以此评估GUS-DS的筛选效率。结果表明GUS-DS将Δmgpex5与Δmgpex7的筛选效率由原来的65.8%和31.2%分别提高到90.6%和82.8%。另外, 还建立了一种适合于GUS-DS的多重PCR法(M-PCR)用于突变体的验证。通过扩增目标位点的不同区段, 可以有效区分突变体、野生型和随机插入转化子。M-PCR法验证突变体简便、迅速, 可信度与Southern杂交相同。GUS-DS及M-PCR为功能基因组学及生物工程的研究提供了有力的工具。     

Arginine and proline genes ofAspergillus niger

Summary Aspergillus niger mutants defective in arginine or proline biosynthesis have been isolated and 12 genetic loci were identified. Mutation was induced by low doses UV, and mutants were isolated after filtration enrichment. The mutants were classified according to their phenotype in growth tests and were further characterized in complementation tests. The arginine auxotrophic mutants represent nine complementation groups. Three additional complementation groups were found for mutants that could grow on proline (two of them on arginine too). Linkage group analysis was done in somatic diploids obtained from a mutant and a master strain with genetic markers on six chromosomes. Thearg genes belong to six different linkage groups and thepro genes to two. Onearg-mutant could be complemented by transformation with theA. nidulans arg B ⁺ gene, and thisA. niger gene thus appeared to be homologous to theA. nidulans arg B. We isolated anA. niger strain with theargB gene tightly linked with thenicA1 marker. This strain is very suitable as acceptor for transformation with anargB-plasmid, because transformants with inserts on the homologous site can be recognized and analyzed genetically using thenicA1 marker gene.     

ThyA as a selection marker in construction of food-grade host-vector and integration systems for Streptococcus thermophilus

We constructed food-grade host-vector and integration systems for Streptococcus thermophilus by using a thymidylate synthase gene (thyA) as the selection marker. Two thyA genes, thyA(St) and thyA(Lb), were cloned from S. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, respectively. Thymidine-requiring mutants of S. thermophilus were obtained after successive cultures in the presence of trimethoprim, and one of them, TM1-1, was used as the host. Food-grade vectors were constructed by using either thyA(St) or thyA(Lb) as the selection marker. Transformants of TM1-1 created by using these vectors were selected for thymidine autotrophy as efficiently as for erythromycin resistance. By using the host-vector system developed in this way, a foreign amylase gene (amyA) was expressed in TM1-1 and was also integrated into the chromosome by use of a temperature-sensitive integration vector constructed with thyA(Lb) as the selection marker via a double-crossover event. The results obtained show that thyA is an efficient and safe selection marker for S. thermophilus that is suitable for food applications.