A manganese requirement for patulin biosynthesis by cultures of Penicillium urticae

Induction of secondary metabolism of Aspergillus terreus ATCC 20542 in the batch bioreactor cultures

Cultivation of Aspergillus terreus ATCC 20542 in a stirred tank bioreactor was performed to induce the biosynthesis of secondary metabolites and provide the bioprocess-related insights into the metabolic capabilities of the investigated strain. The activation of biosynthetic routes was attempted by the diversification of process conditions and growth media. Several strategies were tested, including the addition of rapeseed oil or inulin, changing the concentration of nitrogen source, reduction of chlorine supply, cultivation under saline conditions, and using various aeration schemes. Fifteen secondary metabolites were identified in the course of the study by using ultra-high performance liquid chromatography coupled with mass spectrometry, namely mevinolinic acid, 4a,5-dihydromevinolinic acid, 3α-hydroxy-3,5-dihydromonacolin L acid, terrein, aspulvinone E, dihydroisoflavipucine, (+)-geodin, (+)-bisdechlorogeodin, (+)-erdin, asterric acid, butyrolactone I, desmethylsulochrin, questin, sulochrin, and demethylasterric acid. The study also presents the collection of mass spectra that can serve as a resource for future experiments. The growth in a salt-rich environment turned out to be strongly inhibitory for secondary metabolism and the formation of dense and compact pellets was observed. Generally, the addition of inulin, reducing the oxygen supply, and increasing the content of nitrogen source did not enhance the production of examined molecules. The most successful strategy involved the addition of rapeseed oil to the chlorine-deficient medium. Under these conditions, the highest levels of butyrolactone I, asterric acid, and mevinolinic acid were achieved and the presence of desmethylsulochrin and (+)-bisdechlorogeodin was detected in the broth. The constant and relatively high aeration rate in the idiophase was shown to be beneficial for terrein and (+)-geodin biosynthesis.

Production of cercosporin toxin by the phytopathogenic Cercospora fungi is affected by diverse environmental signals

Cercosporin is a polyketide phytotoxin produced by many phytopathogenic Cercospora spp. We investigated environmental signals that have elaborate control of cercosporin production. Light is the most critical factor for cercosporin production. Cercospora nicotianae accumulated substantial quantities of cercosporin only when grown on a particular potato dextrose agar under light but produced little cercosporin on other brands of potato dextrose agar or media with defined ingredients. In addition to light regulation, numerous factors including salts, buffers, and ions markedly affected cercosporin production. By contrast, pH had little effect on cercosporin production. Depletion or alteration of the carbon or nitrogen sources also affected cercosporin production. Production of cercosporin was elevated to varying levels by metal ions, such as cobalt, ferric, manganese, and zinc. Significant differences in cercosporin production were observed among various Cercospora species. Further, regulation of cercosporin production by phosphate buffer, ammonium, LiCl, but not metal ions appeared to occur at transcriptional levels. Expression of the genes involved in cercosporin biosynthesis and regulation decreased markedly and was closely concomitant with the amounts of cercosporin reduced as the fungus was grown on medium containing phosphate, LiCl, ammonium, or dimethyl sulfoxide. The results reveal the complexity of cercosporin production at the physiological and genetic levels. A model delineating regulatory controls of cercosporin biosynthesis is proposed and discussed.

Evaluation of several culture media for production of patulin by Penicillium species

The aim of this study was to evaluate different species of Penicillium to identify those which have the potential to produce the greatest amount of the mycotoxin, patulin. Additionally, six different culture media were compared to determine maximum patulin production. Eleven different strains of Penicillium species were selected because they had previously been reported to be producers of patulin. The strains included Penicillium expansum, Penicillium griseofulvum (formerly Penicillium urticae), Penicillium clavigerum, and Penicillium coprobium and a recent Penicillium sp. isolated from an apple. Cultures were grown in duplicate in three different liquid media: potato dextrose, malt extract, and glucose/yeast extract/peptone, both with and without manganese supplementation. Patulin production was compared at 24, 48, 72, and 96 h. Variability in patulin production occurred among the different species, growth media used, and time of incubation. All three of the P. griseofulvum isolates were the highest producers of patulin at 96 h. For most of the strains, potato dextrose broth supplemented with manganese was optimal for maximum production of patulin. Although P. expansum is frequently cited as the most likely source of patulin in apple juice, certain other Penicillium species are capable of producing more patulin than strains of P. expansum. The apple juice industry should be alert to the possibility that Penicillium species other than P. expansum can be responsible for the occurrence of patulin.