Isolation and analysis of the Penicillium chrysogenum phoA gene encoding a secreted phosphate-repressible acid phosphatase

Secretion of acid phosphatase from extraradical hyphae of the arbuscular mycorrhizal fungus Rhizophagus clarus is regulated in response to phosphate availability

Arbuscular mycorrhizal (AM) fungi increase phosphate (P) uptake by plants. Organic phosphate comprises 30-80% of total P in most agricultural soils. Some plants can utilize organic phosphate by secreting acid phosphatase (ACP) from their roots, especially under low P conditions. Although secretion of ACP from extraradical hyphae of AM fungi has been reported, the specific factors that affect the secretion of ACP are unknown. The objective of the present study was to investigate whether secretion of ACP from extraradical hyphae is induced by low P conditions. First, specimens of Allium fistulosum were either inoculated with the AM fungus Rhizophagus clarus strain CK001 or remained uninoculated and were grown in soil with 0.5 g P₂O₅ kg^-1 soil or without P fertilization using two-compartment pots. Soil solution was collected using mullite ceramic tubes 45 days after sowing. The soil solution was analyzed for ACP activity by using p-nitrophenylphosphate. Second, Ri T-DNA transformed roots (i.e., hairy roots) of Linum usitatissimum inoculated with R. clarus were grown on solid minimal media with two P levels applied (3 and 30 μM P) using two-compartment Petri dishes under in vitro conditions. Hyphal exudates, extraradical hyphae, and hairy roots were collected and analyzed for ACP activity. ACP activity in the soil solution of the hyphal compartment in the A. fistulosum inoculation treatment was higher without P fertilization than with P fertilization. AM colonization also was higher without P fertilization than with P fertilization. In the in vitro two-compartment culture, ACP activity of hyphal exudates and extraradical hyphae were higher under the 3-μM treatment than under the 30-μM treatment. These findings suggest that the secretion of ACP from the extraradical hyphae of R. clarus into the hyphosphere is promoted under low P conditions.

Biochemical properties and possible roles of ectophosphatase activities in fungi

Ectophosphatases are surface membrane-bound proteins whose active sites face the extracellular medium. These enzymes have been reported in several microorganisms including a large number of medically relevant fungal species. An effective technique for identifying ectophosphatases is performing phosphatase activity assays using living intact cells. Biochemical characterization of these activities has shown their differential modulation by classical phosphatase inhibitors, divalent metals and pH range. The physiological roles of ectophosphatases are not well established; however, it has been suggested that these enzymes play important roles in nutrition, proliferation, differentiation, adhesion, virulence and infection. Adhesion to host cells is the first step in establishing a fungal infection and ectophosphatases may be one of the first parasite proteins that come into contact with the host cells. Several results indicate that ectophosphatase activities increase the capacity of fungi to adhere to the host cells. In this context, the present review provides an overview of recent discoveries related to the occurrence and possible roles of ectophosphatase activities in fungal cells.

Reduction of the degradation activity of umami-enhancing purinic ribonucleotide supplement in miso by the targeted suppression of acid phosphatases in the Aspergillus oryzae starter culture

Miso (fermented soybean paste) is a traditional Japanese fermented food, and is now used worldwide. The solid-state culture of filamentous fungus, Aspergillus oryzae, grown on rice is known as rice-koji, and is important as a starter for miso fermentation because of its prominent hydrolytic enzyme activities. Recently, commercial miso products have been supplemented with purinic ribonucleotides, such as inosine monophosphate (IMP) and guanine monophosphate, to enhance the characteristic umami taste of glutamate in miso. Because the purinic ribonucleotides are degraded by enzymes such as acid phosphatases in miso, heat inactivation is required prior to the addition of these flavorings. However, heat treatment is a costly process and reduces the quality of miso. Therefore, an approach to lower acid phosphatase activities in koji culture is necessary. Transcriptional analysis using an A. oryzae KBN8048 rice-koji culture showed that eight of the 13 acid phosphatase (aph) genes were significantly down-regulated by the addition of phosphoric acid in the preparation of the culture in a concentration-dependent manner, while aphC expression was markedly up-regulated under the same conditions. The eight down-regulated genes might be under the control of the functional counterpart of the Saccharomyces cerevisiae transcriptional activator Pho4, which specifically regulates phosphatase genes in response to the ambient phosphate availability. However, the regulatory mechanism of aphC was not clear. The IMP dephosphorylation activities in rice-koji cultures of KBN8048 and the aphC deletion mutant (ΔaphC) were reduced by up to 30% and 70%, respectively, in cultures with phosphoric acid, while protease and amylase activity, which is important for miso fermentation, was minimally affected. The miso products fermented using the rice-koji cultures of KBN8048 and ΔaphC prepared with phosphoric acid had reductions in IMP dephosphorylation activity of 80% and 90%, respectively, without any adverse effects on amylase and protease activities. Thus, preparing the A. oryzae rice-koji culture under phosphate-sufficient conditions preferentially produces a fermentation starter of miso exhibiting low purinic ribonucleotide dephosphorylation activity. Moreover, aphC is a potential breeding target to reduce purinic ribonucleotide degradation activity further in commercial miso products.

Structure and expression of two genes encoding secreted acid phosphatases under phosphate-deficient conditions in Pholiota nameko strain N2

Twenty-three polypeptides secreted in response to a deficiency of inorganic phosphate (Pi) were previously found by two-dimensional polyacrylamide gel electrophoresis analysis in mycelia of Pholiota nameko strain N2. In this study, N-terminal sequencing revealed three of them to be identical to known acid phosphatases of P. nameko strain N114. Two cDNAs and the corresponding genomic DNAs of genes PNAP1 and PNAP2 which encode two of the three acid phosphatases were cloned. The deduced amino acid sequences of PNAP1 and PNAP2 showed high similarity to other fungal acid phosphatases and contained a putative catalytic active site of acid phosphatase. PNAP1 and PNAP2 are comprised of five and seven exons interrupted by four and six introns, respectively. Their promoter regions include two cis-acting elements found in Pi deficiency-inducible genes of Saccharomyces cerevisiae, together with several known functional elements such as a TATA box. Northern blot analysis showed that PNAP1 and PNAP2 are expressed in response to a deficiency of Pi.

Characterization of a cell-wall acid phosphatase (PhoAp) in Aspergillus fumigatus

In the filamentous fungus Aspergillus fumigatus, the vast majority of the cell-wall-associated proteins are secreted proteins that are in transit in the cell wall. These proteins can be solubilized by detergents and reducing agents. Incubation of a SDS/beta-mercaptoethanol-treated cell-wall extract with various recombinant enzymes that hydrolyse cell-wall polysaccharides resulted in the release of a unique protein in minute amounts only after incubation of the cell wall in the presence of 1,3-beta-glucanase. Sequence analysis and biochemical studies showed that this glycoprotein, with an apparent molecular mass of 80 kDa, was an acid phosphatase (PhoAp) that was active on both phosphate monoesters and phosphate diesters. PhoAp is a glycosylphosphatidylinositol-anchored protein that was recovered in the culture filtrate and cell-wall fraction of A. fumigatus after cleavage of its anchor. It is also a phosphate-repressible acid phosphatase. The absence of PhoAp from a phosphate-rich medium was not associated with a reduction in fungal growth, indicating that this cell-wall-associated protein does not play a role in the morphogenesis of A. fumigatus.

Proteome analysis of Aspergillus fumigatus identifies glycosylphosphatidylinositol-anchored proteins associated to the cell wall biosynthesis

Previous studies in Aspergillus fumigatus (Mouyna I., Fontaine T., Vai M., Monod M., Fonzi W. A., Diaquin M., Popolo L., Hartland R. P., Latgé J.-P, J. Biol. Chem. 2000, 275, 14882-14889) have shown that a glucanosyltransferase playing an important role in fungal cell wall biosynthesis is glycosylphosphatidylinositol (GPI) anchored to the membrane. To identify other GPI-anchored proteins putatively involved in cell wall biogenesis, a proteomic analysis has been undertaken in A. fumigatus and the protein data were matched with the yeast genomic data. GPI-anchored proteins of A. fumigatus were released from membrane preparation by an endogenous GPI-phospholipase C, purified by liquid chromatography and separated by two-dimensional electrophoresis. They were characterized by their peptide mass fingerprint through matrix-assisted laser desorption/ionization-time of flight-(MALDI-TOF)-mass spectrometry and by internal amino acid sequencing. Nine GPI-anchored proteins were identified in A. fumigatus. Five of them were homologs of putatively GPI-anchored yeast proteins (Csa1p, Crh1p, Crh2p, Ecm33p, Gas1p) of unknown function but shown by gene disruption analysis to play a role in cell wall morphogenesis. In addition, a comparative study performed with chitin synthase and glucanosyl transferase mutants of A. fumigatus showed that a modification of the growth phenotype seen in these mutants was associated to an alteration of the pattern of GPI-anchored proteins. These results suggest that GPI-anchored proteins identified in this study are involved in A. fumigatus cell wall organization.

Secretion of an acid phosphatase (SapM) by Mycobacterium tuberculosis that is similar to eukaryotic acid phosphatases

Mycobacterium tuberculosis secretes a large number of polypeptides with broad biological and immunological functions. We describe here the characterization of a 28-kDa acid phosphatase of M. tuberculosis (SapM) localized to the culture filtrate. The mature protein demonstrated biochemical characteristics similar to those of the bacterial nonspecific acid phosphatases. However, SapM yielded significant sequence homology to fungal acid phosphatases and not those of bacteria. Thus, SapM may represent a new class of bacterial nonspecific acid phosphatases.

Synthesis and secretion of phosphatases by endophytic isolates of Colletotrichum musae grown under conditions of nutritional starvation

Even though fungal phosphatases are widely used to study ambient-regulated gene expression, little is known about these enzymes in the agriculturally important genus Colletotrichum. We have therefore identified several phosphatase activities in endophytic isolates of Colletotrichum musae grown under conditions of nutritional sufficiency or starvation for sources of phosphorus (P), nitrogen (N), carbon (C), and sulphur (S). These enzyme forms could be distinguished by substrate specificity, optimum pH, activation and inhibition by some substances, response to nutritional starvation, and pattern of migration in native gel electrophoresis. At least four individual phosphatase activities were identified under the growth conditions employed. A pH 5.0 acid phosphatase and an Mg(2+)-dependent pH 7.5 phosphodiesterase were expressed under all growth conditions at constant rates. Under conditions of P-starvation, derepression of a major pH 6.0-acid phosphatase was observed in cell-free extracts and the culture medium. A synthesis of alkaline phosphatase activities followed a more distinct pattern. Under conditions of nutritional sufficiency of P- or N-starvation, only a single intracellular enzyme form (optimum pH 10) was observed, which was resolved as a single electrophoretic activity band. However, in media lacking C or S sources additional alkaline phosphatase forms were derepressed with a concomitant increase in the overall enzyme activity level measured at pH 10. To our knowledge, this report represents the most detailed study of phosphatases in Colletotrichum and the first partial characterization of the phosphatase system in an endophytic fungus.

Heterologous protein secretion directed by a repressible acid phosphatase system of Kluyveromyces lactis: characterization of upstream region-activating sequences in the KIPHO5 gene

Transcription of the repressible acid phosphatase gene (KIPHO5) in Kluyveromyces lactis is strongly regulated in response to the level of inorganic phosphate (Pi) present in the growth medium. We have begun a study of the promoter region of this gene in order to identify sequences involved in the phosphate control of KIPHO5 expression and to design new expression-secretion systems in K. lactis. Deletion analysis and directed mutagenesis revealed two major identical upstream activating sequences (UAS) CACGTG at positions -430 (USA1) and -192 (UAS2) relative to the ATG initiation codon. These sequences are identical to those described for Saccharomyces cerevisiae for the binding of Pho4p. Deletion or directed mutagenesis of either one or both UAS reduce KIPHO5 expression by the same amount (approximately 80%). When fused to the coding region of trout growth hormone cDNA (tGH-II), the promoter and signal peptide-encoding region of the phosphate-repressible KIPHO5 gene drives the expression of this gene and the secretion of the tGHII protein. Synthesis of tGHIIp in K. lactis transformants carrying this construct was found to be regulated by the Pi present in the medium; depression of heterologous protein expression can therefore be achieved by lowering the Pi concentration.

The KIPHO5 gene encoding a repressible acid phosphatase in the yeast Kluyveromyces lactis: cloning, sequencing and transcriptional analysis of the gene, and purification and properties of the enzyme

A secreted phosphate-repressible acid phosphatase from Kluyveromyces lactis has been purified and the N-terminal region and an internal peptide have been sequenced. Using synthetic oligodeoxyribonucleotides based on the sequenced regions, the genomic sequence, KIPHO5, encoding the protein has been isolated. The deduced protein, named KIPho5p, consists of 469 amino acids and has a molecular mass of 52520 Da (in agreement with the data obtained after treatment of the protein with endoglycosidase H). The purified enzyme shows size heterogeneity, with an apparent molecular mass in the range 90-200 kDa due to the carbohydrate content (10 putative glycosylation sites were identified in the sequence). A 16 amino acid sequence at the N-terminus is similar to previously identified signal peptides in other fungal secretory proteins. The putative signal peptide is removed during secretion since it is absent in the mature secreted acid phosphatase. The gene can be induced 400-600-fold by phosphate starvation. Consensus signals corresponding to those described for Saccharomyces cerevisiae PHO4- and PHO2-binding sites are found in the 5' region. Northern blot analysis of total cellular RNA indicates that the KIPHO5 gene codes for a 1.8 kb transcript and that its expression is regulated at the transcriptional level. Chromosomal hybridization indicated that the gene is located on chromosome II. The KIPHO5 gene of K. lactis is able to functionally complement a pho5 mutation of Sacch. cerevisiae. Southern blot experiments, using the KIPHO5 gene as probe, show that some K. lactis reference strains lack repressible acid phosphatase, revealing a different gene organization for this kind of multigene family of proteins as compared to Sacch. cerevisiae.

Regulated system for heterologous gene expression in Penicillium chrysogenum

A system for regulated heterologous gene expression in the filamentous fungus Penicillium chrysogenum was established. This is the first heterologous expression system to be developed for this organism. Expression of a recombinant fungal xylanase gene (xylp) and the cDNA for the human tear lipocalin (LCNI) was achieved by placing the encoding sequences under the control of the repressible acid phosphatase gene (phoA) promoter of P. chrysogenum. Secreted recombinant proteins were detected in the growth media of transformed P. chrysogenum cells by means of bioassays, zymogramography, and Western blotting. Levels of transcription and amounts of recombinant proteins secreted varied among transformants, mainly due to the copy number and the integration site of the expression vector on the fungal chromosome.

Developments in biotechnological research in Austria

Austria is a small European country with a small number of universities and biotechnological industries, but with great efforts in the implementation of environmental consciousness and corresponding legal standards. This review attempts to describe the biotechnological landscape of Austria, thereby focusing on the highlights in research by industry, universities, and research laboratories, as published during 1990 to early 1995. These will include microbial metabolite (organic acids, antibiotics) and biopolymer (polyhydroxibutyrate, S-layers) production; enzyme (cellulases, hemicellulases, ligninases) technology and biocatalysis; environmental biotechnology; plant breeding and plant protection; mammalian cell products; fermenter design; and bioprocess engineering.

Cloning, structural organization and regulation of expression of the Penicillium chrysogenum paf gene encoding an abundantly secreted protein with antifungal activity

An abundantly secreted, highly basic 12-kDa protein (PAF) was purified from the culture medium of Penicillium chrysogenum (Pc). Based on the N-terminal amino acid (aa) sequence of the protein, an oligodeoxyribonucleotide probe was derived and used for amplification of the encoding cDNA by PCR. This cDNA fragment encodes a Cys-rich preproprotein of 92 aa which appears to be processed to a mature product of 55 aa. The deduced aa sequence of the preproprotein reveals 42.6% identity to an antifungal protein (AFP) of Aspergillus giganteus. Agar diffusion tests confirmed that the Pc protein exhibits antifungal activity. In order to investigate the promoter region and the structural organization of the paf gene, a genomic 6-kb fragment was isolated and partially sequenced. Comparison of the nucleotide sequence of the genomic fragment and the cDNA clone revealed the presence of a coding region of 279 bp which is interrupted by two introns of 76 and 68 bp in length. In the promoter region, a typical TATA box, a motif resembling the fungal carbon catabolite repression element, as well as several putative GATA factor binding motifs, were found. Northern blot analysis indicated that the regulation of paf expression occurs at the level of mRNA transcription and is under control of carbon catabolite and nitrogen metabolite repression regulatory circuits.

The Aspergillus niger (ficuum) aphA gene encodes a pH 6.0-optimum acid phosphatase

We have used the Aspergillus niger (An) aphA gene as a probe and cloned the A. ficuum (Af) SRRC 265 gene encoding an extracellular pH 6.0-optimum acid phosphatase (APase6) from a genomic library. The identity of the Af aphA gene was confirmed and its nucleotide (nt) sequence verified by comparing its deduced amino acid (aa) sequence to that of purified Af APase6. A comparison of the nt sequences of the An and Af genes suggested that errors were made in the previously reported An aphA sequence. Several regions of the An aphA were resequenced and the mistakes corrected. With its nt sequence corrected, the An aphA is nearly identical to the cloned Af gene encoding APase6, and in 90.4% agreement in the coding regions. Both genes have three conserved introns and when translated, both nt sequences code for a polypeptide of 614 aa. There is now evidence that the two cloned genes are homologous and code for acid phosphatases that are 96% identical.

Sequence and structure of Penicillium chrysogenum phoG, homologous to an acid phosphatase-encoding gene of Aspergillus nidulans

A Penicillium chrysogenum (Pc) gene (phoG), homologous to an Aspergillus nidulans (An) gene which confers phosphate-non-repressible acid phosphatase (APase) activity, has been cloned and sequenced. The 2.9-kb genomic sequence corresponds to two ORFs of 149 and 1630 bp encoding a protein of 593 amino acids (aa). As verified by cDNA sequencing, the coding region is interrupted by an 85-bp intron. The deduced aa sequence of phoG reveals 61% aa identity to the translated long ORF of the An APase-encoding gene. Northern blot analysis indicated a 2.3-kb transcript in approximately equivalent amount in mycelia grown under different phosphate concentrations.

Detection of a protein which binds specifically to the upstream region of the pcbAB gene in Penicillium chrysogenum

The upstream region of the pcbAB gene from Penicillium chrysogenum was screened for protein-binding sites using an electromobility shift assay. A specific protein/DNA interaction was detected within a fragment covering the region -387 to -242 relative to the pcbAB translational start codon. The appearance of this protein and pcbAB mRNA in culture extracts occurred at the same time point in fermentations, suggesting that the protein might be a transcription activator. The putative upstream activating sequence was located more precisely using cross-competition assays. These indicated the involvement of the 7-bp motif TGCCAAG in the binding of the protein.

Synonymous codon usage in Kluyveromyces lactis

The nature and variation of synonymous codon usage in 47 open reading frames from Kluyveromyces lactis have been investigated. Using multivariate statistical analysis, a single major trend among K. lactis genes was identified that differentiates among genes by expression level: highly expressed genes have high codon usage bias, while genes of low expression level have low bias. A relatively minor secondary trend differentiates among genes according to G+C content at silent sites. In these respects, K. lactis is similar to both Saccharomyces cerevisiae and Candida albicans, and the same 'optimal' codons appear to be selected in highly expressed genes in all three species. In addition, silent sites in K. lactis and S. cerevisiae have similar G+C contents, but in C. albicans genes they are more A+T-rich. Thus, in all essential features, codon usage in K. lactis is very similar to that in S. cerevisiae, even though silent sites in genes compared between these two species have undergone sufficient mutation to be saturated with changes. We conclude that the factors influencing overall codon usage, namely mutational biases and the abundances of particular tRNAs, have not diverged between the two species. Nevertheless, in a few cases, codon usage differs between homologous genes from K. lactis and S. cerevisiae. The strength of codon usage bias in cytochrome c genes differs considerably, presumably because of different expression patterns in the two species. Two other, linked, genes have very different G+C content at silent sites in the two species, which may be a reflection of their chromosomal locations. Correspondence analysis was used to identify two open reading frames with highly atypical codon usage that are probably not genes.

Characterization of an Aspergillus nidulans genomic DNA fragment conferring phosphate-non-repressible acid-phosphatase activity

A clone from an Aspergillus nidulans library was identified by its ability to confer enhanced staining for acid phosphatase (APase) activity upon phosphatase-deficient A. nidulans mutants. This APase activity is not repressed by high phosphate concentrations in the medium. The 2.9-kb nucleotide sequence in the region of the clone responsible for the effect reveals two potential protein-coding genes with a common N terminus. One corresponds to an open reading frame (ORF) with no introns, encoding 330 amino acids (aa). The other, shorter gene encoding 113 or 117 aa has the first 65 or 69 codons in common with the long ORF; then, after a single 165-nt intron with a fungal consensus lariat sequence and splice junctions, there are a further 48 codons in a different reading frame. Both correspond in sense direction, and the shorter gene in length, with the only detectable transcript in this region, but both differ from all known APase sequences. The possible identity of these ORFs with the pacG gene is discussed.

Cloning, characterization and overexpression of the phytase-encoding gene (phyA) of Aspergillus niger

Phytase catalyzes the hydrolysis of phytate (myo-inositol hexakisphosphate) to myo-inositol and inorganic phosphate. A gene (phyA) of Aspergillus niger NRRL3135 coding for extracellular, glycosylated phytase was isolated using degenerate oligodeoxyribonucleotides deduced from phytase amino acid (aa) sequences. Nucleotide (nt) sequence analysis of the cloned region revealed the presence of an open reading frame coding for 467 aa and interrupted once by an intron of 102 bp in the 5' part of the gene. The start codon is followed by a sequence coding for a putative signal peptide. Expression of phyA is controlled at the level of mRNA accumulation in response to inorganic phosphate levels. After cell growth in low-phosphate medium, a transcript of about 1.8 kb was visualized. Transcription of phyA initiates at at least seven start points within a region located 45-25 nt upstream from the start codon. In transformants of A. niger, expression of multiple copies of phyA resulted in up to more than tenfold higher phytase levels than in the wild-type strain.

Cloning and structural organization of a xylanase-encoding gene from penicillium chrysogenum

The filamentous fungus, Penicillium chrysogenum, is able to grow on xylan as a sole carbon source. Under these conditions, high levels of a xylanase (XYLP) are secreted into the medium. After purification and characterization of this enzyme, we have isolated both the encoding cDNA and the genomic sequence by using oligodeoxyribonucleotides derived from partial amino acid (aa) sequences of the purified enzyme. The gene is approximately 1.6 kb in length, and comparison of the nucleotide (nt) sequence of the genomic and the cDNA clone revealed the presence of ten exons and nine introns. All intron/exon splice junctions exactly follow the GT/AG rule, except for the seventh intron which shows atypical AT/AC splice sites. The immediate 5'-flanking region of the first exon contains one putative CCAAT consensus sequence and a perfect TATA box. Primer extension analysis revealed two transcription start points located 38 and 34 nt upstream from the ATG start codon. A sequence of 23 aa representing a typical signal peptide is present at the N terminus of the deduced aa sequence. Northern blot analysis of total cellular RNA indicated that xylP encodes a 1.3-kb transcript which is induced by xylan. The aa sequence of XYLP shows considerable homology to high-M(r) acidic xylanases (Xln) and cellulases from different bacteria, yeasts and fungi.