Searching for new-type antifungal drugs (an outline for possible new strategies)

The small molecular mass antifungal protein of Penicillium chrysogenum--a mechanism of action oriented review

The β-lactam producing filamentous fungus Penicillium chrysogenum secretes a 6.25 kDa small molecular mass antifungal protein, PAF, which has a highly stable, compact 3D structure and is effective against a wide spectrum of plant and zoo pathogenic fungi. Its precise physiological functions and mode of action need to be elucidated before considering possible biomedical, agricultural or food technological applications. According to some more recent experimental data, PAF plays an important role in the fine-tuning of conidiogenesis in Penicillium chrysogenum. PAF triggers apoptotic cell death in sensitive fungi, and cell death signaling may be transmitted through two-component systems, heterotrimeric G protein coupled signal transduction and regulatory networks as well as via alteration of the Ca(2+) -homeostasis of the cells. Possible biotechnological applications of PAF are also outlined in the review.

MeaB-dependent nutrition sensing regulates autolysis in carbon starved Aspergillus nidulans cultures

Carbon starvation induced autolysis is an active process of self-digestion and is under complex regulation in Aspergillus nidulans. In this study we investigated how autolysis depends on the composition of the culture medium, especially on the presence of yeast extract. We demonstrated that the rate of autolytic cell wall degradation as well as the extracellular chitinase and proteinase productions significantly decreased in the presence of this nutrient. The effect of yeast extract on carbon starved cultures was independent of loss-of-function mutations in the carbon and nitrogen regulatory genes creA and areA and in the heterotrimeric G protein signalling genes fadA and ganB. In contrast, the nitrogen regulating transcription factor MeaB was involved in the yeast-extract-mediated repression of autolysis. Reverse transcriptase - polymerase chain reaction (RT-PCR) experiments demonstrated that MeaB affects the FluG-BrlA sporulation regulatory pathway by affecting transcription of brlA, a gene also initiating the autolytic cell wall degradation in this fungus.

Regulation of autolysis in Aspergillus nidulans

In terms of cell physiology, autolysis is the centerpiece of carbon-starving fungal cultures. In the filamentous fungus model organism Aspergillus nidulans, the last step of carbon-starvation-triggered autolysis was the degradation of the cell wall of empty hyphae, and this process was independent of concomitantly progressing cell death at the level of regulation. Autolysis-related proteinase and chitinase activities were induced via FluG signaling, which initiates sporulation and inhibits vegetative growth in surface cultures of A. nidulans. Extracellular hydrolase production was also subjected to carbon repression, which was only partly dependent on CreA, the main carbon catabolite repressor in this fungus. These data support the view that one of the main functions of autolysis is supplying nutrients for sporulation, when no other sources of nutrients are available. The divergent regulation of cell death and cell wall degradation provides the fungus with the option to keep dead hyphae intact to help surviving cells to absorb biomaterials from dead neighboring cells before these are released into the extracellular space. The industrial significance of these observations is also discussed in this paper.

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.

Anticandidal low molecular compounds from higher plants with special reference to compounds from essential oils

The most active low molecular weight compounds from higher plants against Candida species are compiled from a database of antimicrobials (Amicbase) to find out new hints on their mechanism of action. The selected compounds possess strong inhibitory activities in vitro against Candida species either in the agar diffusion test, bioautography, agar dilution test, serial dilution test, or activity in the vapour phase. The test conditions are listed thoroughly and aspects of the different methods and recent developments in the testing of anticandidal drugs are discussed. The anticandidal spectra of drugs, antiseptics, and disinfectants licensed on the major markets are given for comparison of activities with compounds from natural sources. So far known mechanisms of action are described and some new structure-activity relationships are deduced from relationships between biological activities and chemical and physical parameters. Main specific targets of natural anticandidals are the ergosterol pathway, respiratory chain, and chitin biosynthesis.

Distribution and susceptibility of Candida species isolated in the Medical University of Debrecen

Data of Candida albicans and non-albicans Candida species isolated during the 1997-2000 period in the Medical and Health Science Center of the University of Debrecen are analysed. The number of yeast isolates increased from 408 to 1213 per year during this period. Dominance of C. albicans has been persistent, but a slight increase of C. glabrata and C. krusei could be observed. Distribution of different Candida species isolated from 16 body sites indicates that C. albicans seems to be still the most aggressive Candida species. Investigation of 244 urinary Candida isolates (parallel with bacterial cultures) suggests that tha aetiological role of Candida species in the pathogenesis of urinary tract infections can be hypothesized if colony forming unit (CFU) number of yeasts is higher than 10(4)/ml and bacteria are present in low CFU number or are absent. Antifungal susceptibility testing of C. albicans, C. glabrata, C. tropicalis and C. krusei against Flucytosine, Amphotericin-B, Miconazole, Ketoconazole and Fluconazole suggests that Amphotericin-B is still the most effective antifungal agent. Finally, the problems in judging the aetiological role of isolated Candida species in the pathogenesis of different types of diseases are critically discussed.

In vitro antimicrobial activity of 3,4-dihydro-s-triazinobenzimidazole derivatives

Among 31 3,4-dihydro-s-triazinobenzimidazole derivatives tested 12 compounds showed in vitro antimicrobial activity against G+ bacteria. Best results were obtained with substances containing naphthyl or halogenated phenyl group on the triazine ring. The tested derivatives had no significant in vitro antimicrobial activity against either the used G- species or fungi.

The glutathione metabolism of the beta-lactam producer filamentous fungus Penicillium chrysogenum

Glutathione (gamma-L-glutamyl-L-cysteinyl-glycine; GSH) shares structural similarities with the beta-lactam biosynthetic intermediate ACV-tripeptide (delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine). Not surprisingly, GSH has been reported to inhibit the beta-lactam biosynthetic machinery quite effectively and, hence, strategies to decrease the intracellular GSH concentrations without influencing negatively the physiological status of idiophasic mycelia would attract industrial interests. Here we present a detailed map of the GSH metabolic network of P. chrysogenum and show a promising way to keep the GSH pool selectively down under penicillin producing conditions. This procedure includes a well-controlled and transient lowering of pH at the beginning of the production phase, and it relies on the GSH-dependent detoxification of the protonophore penicillin side-chain precursors phenoxyacetic acid (POA) and phenylacetic acid (PA). Encouraging preliminary fed-batch fermentation experiments have been performed to test this technological proposal. Interestingly, the mechanism of the activation of POA and PA to the appropriate CoA derivatives has remained yet to be answered but the involvement of GSH seems to be rather unlikely in this case. Our data also challenge the hypothesis that the formation of different kinds of penicillins would be an alternative to GSH-dependent detoxification processes in P. chrysogenum.