The formation of N-acetyl-β-D-hexosaminidase is repressed by glucose inPenicillium chrysogenum

Nitrogen supply rate regulates microbial resource allocation for synthesis of nitrogen-acquiring enzymes

Although microorganisms will preferentially allocate resources to synthesis of nitrogen (N)-acquiring enzymes when soil N availability is low according to the resource allocation model for extracellular enzyme synthesis, a robust link between microbial N-acquiring enzyme activity and soil N concentration has not been reported. To verify this link, we measured several indices of soil N availability and enzyme activity of four N-acquiring enzymes [N-acetyl-β-glucosaminidase (NAG), protease (PR), urease (UR), and L-asparaginase (LA)] and a carbon (C)-acquiring enzyme [β-D-glucosidase (BG)] in arable and forest soils. Although the ratios of NAG/BG and PR/BG were not significantly related with indices of soil N availability, ratios of LA/BG and UR/BG were strongly and negatively related with potentially mineralizable N estimated by aerobic incubation but not with pools of labile inorganic N and organic N. These results suggest that microorganisms might allocate their resources to LA and UR synthesis in response to N supply rate rather than the size of the easily available N pools. It was also suggested that the underlying mechanism for synthesis was different between these N-acquiring enzymes in soil microorganisms: microbial LA and UR were primarily synthesized to acquire N, whereas NAG and PR syntheses were regulated not only by N availability but also by other factors.

Chitinase but N-acetyl-β-D-glucosaminidase production correlates to the biomass decline in Penicillium and Aspergillus species

Hydrolytic enzyme production is typical of the autolysis in filamentous fungi; however, less attention has been given to the physiological role of the enzymes. Here, the aim was to investigate the possible relation of the chitinolytic enzymes to the changes in the biomass in some filamentous fungi of high importance for pharmaceutical or food industry. In Penicillium and Aspergillus filamentous fungi, which showed different characteristics in submerged cultures, the growth and biomass decline rates were calculated and correlated to the chitinase and N-acetyl-β-D-glucosaminidase enzyme productions. Correlation was found between the biomass decrease rate and the chitinase level at the stationary growth phase; while chitinase production covariates negatively with N-acetyl-β-D-glucosaminidase activities. The chitinase production and the intensive autolysis hindered the production of N-acetyl-β-D-glucosaminidase and, therefore, could hinder the cell death in the cultures.

Effect of cell wall integrity stress and RlmA transcription factor on asexual development and autolysis in Aspergillus nidulans

The cell wall integrity (CWI) signaling pathway is responsible for cell wall remodeling and reinforcement upon cell wall stress, which is proposed to be universal in fungal cultures. In Aspergillus nidulans, both the deletion of rlmA encoding the RlmA transcription factor in CWI signaling and low concentrations of the cell wall polymer intercalating agent Congo Red caused significant physiological changes. The gene deletion mutant ΔrlmA strain showed decreased CWI and oxidative stress resistances, which indicated the connection between the CWI pathway and the oxidative stress response system. The Congo Red stress resulted in alterations in the cell wall polymer composition in submerged cultures due to the induction of the biosynthesis of the alkali soluble fraction as well as the hydrolysis of cell wall biopolymers. Both RlmA and RlmA-independent factors induced by Congo Red stress regulated the expression of glucanase (ANID_00245, engA) and chitinase (chiB, chiA) genes, which promoted the autolysis of the cultures and also modulated the pellet sizes. CWI stress and rlmA deletion affected the expression of brlA encoding the early conidiophore development regulator transcription factor BrlA and, as a consequence, the formation of conidiophores was significantly changed in submerged cultures. Interestingly, the number of conidiospores increased in surface cultures of the ΔrlmA strain. The in silico analysis of genes putatively regulated by RlmA and the CWI transcription factors AnSwi4/AnSwi6 in the SBF complex revealed only a few jointly regulated genes, including ugmA and srrA coding for UgmA UDP-galactopyranose mutase and SrrA stress response regulator, respectively.

Comparative studies of differential expression of chitinolytic enzymes encoded by chiA, chiB, chiC and nagA genes in Aspergillus nidulans

N-Acetyl-D-glucosamine, chito-oligomers and carbon starvation regulated chiA, chiB, and nagA gene expressions in Aspergillus nidulans cultures. The gene expression patterns of the main extracellular endochitinase ChiB and the N-acetyl-beta-D-glucosaminidase NagA were similar, and the ChiB-NagA enzyme system may play a morphological and/or nutritional role during autolysis. Alterations in the levels of reactive oxygen species or in the glutathione-glutathione disulfide redox balance, characteristic physiological changes developing in ageing and autolyzing fungal cultures, did not affect the regulation of either the growth-related chiA or the autolysis-coupled chiB genes although both of them were down-regulated under diamide stress. The transcription of the chiC gene with unknown physiological function was repressed by increased intracellular superoxide concentration.

The nagA gene of Penicillium chrysogenum encoding beta-N-acetylglucosaminidase

We purified the beta-N-acetylglucosaminidase from the filamentous fungus Penicillium chrysogenum and its N-terminal sequence was determined, showing the presence of a mixture of two proteins (P1 and P2). A genomic DNA fragment was cloned by using degenerated oligonucleotides from the Nt sequences. The nucleotide sequence showed the presence of an ORF (nagA gene) lacking introns, with a length of 1791 bp, and coding for a protein of 66.5 kDa showing similarity to acetylglucosaminidases. The NagA deduced protein includes P1 and P2 as incomplete forms of the mature protein, and contains putative features for protein maturation: an 18-amino acid signal peptide, a KEX2 processing site, and four glycosylation motifs. The sequence just after the signal peptide corresponds to P2 and that after the KEX2 site to P1. The nagA transcript has a size of about 2.1 kb and is present until the end of the fermentation process for penicillin production. NagA is one of the most largely represented proteins in P. chrysogenum, increasing along the fermentation process. The suitability of the nagA promoter (PnagA) for gene expression in fungi was demonstrated by expressing the bleomycin resistance gene (ble(R)) from Streptoalloteichus hindustanus in P. chrysogenum.

Penicillium chrysogenum glucose oxidase - a study on its antifungal effects

AIMS

Purification and characterization of the high molecular mass Candida albicans-killing protein secreted by Penicillium chrysogenum.

METHODS AND RESULTS

The protein was purified by a combination of ultrafiltration, chromatofocusing and gel filtration. Enzymological characteristics [relative molecular mass (M(r)) = 155 000, subunit structure alpha(2) with M(r,alpha) = 76 000, isoelectric point (pI) = 5.4] were determined using SDS-PAGE and 2D-electrophoresis. N-terminal amino acid sequencing and homology search demonstrated that the antifungal protein was the glucose oxidase (GOX) of the fungus. The enzyme was cytotoxic for a series of bacteria, yeasts and filamentous fungi. Vitamin C (1.0 mg ml(-1)) prevented oxidative cell injuries triggered by 0.004 U GOX in Emericella nidulans cultures but bovine liver catalase was ineffective even at a GOX : catalase activity ratio of 0.004 : 200 U. A secondary inhibition of growth in E. nidulans cultures by the oxygen-depleting GOX-catalase system was likely to replace the primary inhibition exerted by H(2)O(2).

CONCLUSIONS

Penicillium chrysogenum GOX possesses similar enzymological features to those described earlier for other Penicillium GOXs. Its cytotoxicity was dependent on the inherent antioxidant potential of the test micro-organisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

Penicillium chrysogenum GOX may find future applications in glucose biosensor production, the disinfection of medical implants or in the food industry as an antimicrobial and/or preservative agent.

Physiological and morphological changes in autolyzingAspergillus nidulans cultures

Physiological and morphological changes in carbon-limited autolyzing cultures of Aspergillus nidulans were described. The carbon starvation arrested conidiation while the formation of filamentous and "yeast-like" hyphal fragments with profoundly altered metabolism enabled the fungus to survive the nutritional stress. The morphological and physiological stress responses, which maintained the cellular integrity of surviving hyphal fragments at the expense of autolyzing cells, were highly concerted and regulated. Moreover, sublethal concentrations of the protein synthesis inhibitor cycloheximide or the mitochondrial uncoupler 2,4-dinitrophenol completely blocked the autolysis. In accordance with the propositions of the free-radical theory of ageing reactive oxygen species accumulated in the surviving fragments with a concomitant increase in the specific superoxide dismutase activity and a continuous decrease in cell viability. Glutathione was degraded extensively in carbon-starving cells due to the action of gamma-glutamyltranspeptidase, which resulted in a glutathione-glutathione disulfide redox imbalance during autolysis.

Carbon source regulation of beta-galactosidase biosynthesis in Penicillium chrysogenum

Growth and beta-galactosidase activity of the penicillin producer industrial Penicillium chrysogenum NCAIM 00237 strain were examined using different carbon sources. Good growth was observed using glucose, sucrose, glycerol and galactose, while growth on lactose was substantially slower. beta-Galactosidase activity was high on lactose and very low on all the other carbon sources tested. In glucose grown cultures after exhaustion of glucose as repressing carbon source a derepressed low level of the enzyme was observed. cAMP concentration in lactose grown cultures was relatively high, in glucose grown cultures was low. Caffeine substantially decreased glucose consumption and growth but did not increase beta-galactosidase activity and did not prevent glucose repression which rules out the involvement of cAMP in the regulation of beta-galactosidase biosynthesis in Penicillium chrysogenum.

Glutathione metabolism and dimorphism in Aureobasidium pullulans

Yeast<-->mycelium morphological transitions of Aureobasidium pullulans are influenced by numerous environmental factors. In general, changes in the glutathione (GSH) metabolism of dimorphic fungi may lead to alterations in the reduced thiol status of the cells that are hypothesised to initialise morphological transitions. In accordance with this hypothesis, the specific GSH levels found in A. pullulans yeast cells were always significantly higher than those in mycelia. One the other hand, there was no significant difference between the GSH/GSSG redox status of the cells with either yeast or mycelial morphology. The cascade of events leading to morphological transitions was therefore unlikely to proceed via redox modulation of protein thiols. Although there were morphology-dependent differences in the specific activities of some GSH metabolic enzymes, e.g. glutathione reductase (GR), gamma-glutamyltranspeptidase (gamma GT), glucose-6-phosphate dehydrogenase (G6PD), they were not satisfactory to explain the observed alterations in the intracellular GSH levels. It is noteworthy that very similar specific gamma GT and G6PD activities were found in cells separated from mixed morphology cultures independently of the actual cell morphology. On the other hand, the specific gamma GT and G6PD activities of A. pullulans cells sharing the same morphology but separated from pure and mixed morphology cultures showed marked differences.

Autolysis and aging of Penicillium chrysogenum cultures under carbon starvation: Chitinase production and antifungal effect of allosamidin

In carbon-depleted cultures of Penicillium chrysogenum, age-related chitinases were shown to play a crucial role in both autolysis and fragmentation as indicated by in vivo enzyme inhibition experiments using allosamidin. This pseudotrisaccharide even hindered significantly the outgrowth of new hyphal tips from the surviving yeastlike fragments after glucose supplementation. The antifungal effect of allosamidin on autolyzing P. chrysogenum mycelia was fungistatic rather than fungicidal. In growing hyphae, membrane-bound microsomal chitinase zymogen(s) were detected, which may be indicative of some compartmentalization of these hydrolases. Later, during autolysis, no zymogenic chitinase was detected in any enzyme fraction studied, including microsomes. These observations may explain the different sensitivity of growing and autolyzing mycelia to allosamidin. Chitinases taking part in the age-related fragmentation of hyphae and the outgrowth of surviving hyphal fragments seem to be potent targets for future antifungal drug research.

Cyanide-resistant alternative respiration is strictly correlated to intracellular peroxide levels in Acremonium chrysogenum

A strict correlation between the intensity of the cyanide-resistant alternative respiratory pathway and the intracellular peroxide levels in the cephalosporin C producer filamentous fungus Acremonium chrysogenum was demonstrated. Intracellular peroxide levels increased in a dose-dependent manner after addition of H2O2 to the culture media. A similar phenomenon was observed due to the specific inhibition of catalase by salicylic acid. In both cases, cyanide-resistant respiration was markedly stimulated. On the other hand, both cyanide-resistant respiration and intracellular peroxide levels were effectively suppressed by the lipid peroxyl radical scavenger DL-alpha-tocopherol, which breaks lipid peroxidation chains effectively. Our findings firmly supported the assumption that there is a connection between the intracellular peroxide levels and the intensity of the alternative respiratory pathway in fungi.

Penicillin V production by Penicillium chrysogenum in the presence of Fe3+ and in low-iron culture medium

Late-exponential-phase Penicillium chrysogenum mycelia grown in a complex medium possessed an intracellular iron concentration of 650 mumol/L (2.2 +/- 0.6 mumol per g mycelial dry mass). This iron reserve was sufficient to ensure growth and antibiotic production after transferring mycelia into a defined low-iron minimal medium. Although the addition of Fe3+ to the Fe-limited cultures increased significantly the intracellular iron levels the surplus iron did not influence the production of penicillin V. Supplements of purified major P. chrysogenum siderophores (coprogen and ferrichrome) into the fermentation media did not affect the beta-lactam production and intracellular iron level. Neither 150 nor 300 mumol/L extracellular Fe3+ concentrations disturbed the glutathione metabolism of the fungus, and increased the oxidative stress caused by 700 mmol/L H2O2. Nevertheless, when iron was applied in the FeII oxidation state the oxidative cell injuries caused by the peroxide were significantly enhanced.

Allosamidin inhibits the fragmentation of Acremonium chrysogenum but does not influence the cephalosporin-C production of the fungus

The pseudotrisaccharide allosamidin, a potent inhibitor of chitinases, retarded the fragmentation of hyphae but did not affect the fungal growth and cephalosporin-C production in Acremonium chrysogenum. In vitro inhibition of A. chrysogenum cell-bound chitinase(s) by allosamidin revealed that about 47% of the soluble intracellular chitinase activity was resistant to the inhibitory effect of allosamidin. On the other hand, about 76% of the total chitinase activity localised in both the soluble and insoluble enzyme fractions was effectively inhibited by allosamidin. All the chitinase activities were measured using a new procedure based on purified A. chrysogenum chitin as substrate.

Beta-N-acetylhexosaminidase: a target for the design of antifungal agents

This review provides biochemical, analytical, and biological background information relating to beta-N-acetylhexosaminidase (HexNAc'ase; EC 3.2.1.52) as an emerging target for the design of low-molecular-weight antifungals. The article includes the following: (1) a biochemical description of HexNAc'ase (reaction catalyzed, nomenclature, and mechanism of action) that sets it apart from other, similar enzymes; (2) an overview and a critical evaluation of methods to assay the enzyme, including in crude extracts (photo- and fluorometric procedures with model substrates; HPLC/pulsed amperometric detection of N-acetylglucosamine and chito-oligomers; end-point vs. rate measurements); (3) a summary of some general characteristics of HexNAc'ases from fungi and organisms of other types (Km values, substrate preference, and glycoconjugation); (4) an hypothesis of a specific target function of wall-associated HexNAc'ase (a component of the assembly of surface-located enzymes effecting a continuous turnover and remodelling of the wall fabric through its combined hydrolytic and transglycosylating activities, and a mediator enzyme acting in concert with chitinase and chitin synthase to provide for the controlled lysis and synthesis of chitin during growth); (5) a tabulation of the structural formulae of reaction-based HexNAc'ase inhibitors with Ki values < or = 100 microM (some of them representing transition state mimics that could serve as leads for the development of new antifungals); and (6) an outline of approaches towards the establishment of a three-dimensional model of HexNAc'ase suitable for a truly rational design of antimycotics as well as agricultural fungicides.

NADP-specific glutamate dehydrogenase of Penicillium chrysogenum has a homohexamer structure

The NADP-specific glutamate dehydrogenase of a high beta-lactam producing industrial strain of Penicillium chrysogenum was purified to homogeneity. The enzyme (M(r) = 339,000 +/- 34,000) was demonstrated to have a homohexamer quaternary structure with a subunit molecular mass of M(r) = 56,000 +/- 2000. The N-terminal sequence of the enzyme was also determined and was found to be highly homologous to other fungal NADP-specific glutamate dehydrogenase sequences.