Penicillium paneum is an important contaminant of cereal grains which is able to grow at low temperature, low pH, high levels of carbon dioxide, and under acid conditions. P. paneum produces mycotoxins, which may be harmful to animals and humans. We found that conidia in dense suspensions showed poor germination, suggesting the presence of a self-inhibitor. A volatile compound(s) produced by these high-density conditions also inhibited mycelial growth of different species of fungi belonging to a variety of genera, suggesting a broad action range. The heat-stable compound was isolated by successive centrifugation of the supernatant obtained from spore suspensions with a density of 10 9 conidia ml ؊1 . By using static headspace analyses, two major peaks were distinguished, with the highest production of these metabolites after 22 h of incubation at 25°C and shaking at 140 rpm. Gas chromatography coupled with mass spectra analysis revealed the compounds to be 3-octanone and 1-octen-3-ol. Notably, only the latter compound appeared to block the germination process at different developmental stages of the conidia (swelling and germ tube formation). In this study, 1-octen-3-ol influenced different developmental processes during the P. paneum life cycle, including induction of microcycle conidiation and inhibition of spore germination. Therefore, the compound can be considered a fungal hormone during fungal development.The spore is an important vehicle for distribution or longterm survival of fungi. Conidia are nonmotile asexual spores, which can be produced in very large numbers by fungi belonging to the order Eurotiales. This order, which includes the genera Aspergillus and Penicillium (14), contains many species of food-related fungi. Conidia are dispersed into the air but do not germinate before they reach a suitable substrate. Invariably, germination is inhibited when spores are present in high densities, an effect observed for example in Aspergillus niger and the zygomycete Syncephalastrum racemosum (3,19). This is designated as the crowding effect. Also, in the formation of an adhesive bud on spores of the nematophagous fungus Drechmeria coniospora, there is a clear crowding effect (35). These observations suggest that intercellular signaling prevents premature germination.Acervuli of Colletotrichum spp. form large numbers of conidia embedded in mucilage but not germinating there. From the mucilage that surrounds the conidia of this fungus, a self-inhibitor of germination named mycosporine-alanine has been identified and characterized (26). Germination is also retarded in pustules of rust fungi (Basidiomycetes) where cisferulic acid methyl ester and cis-3,4-dimethoxycinnamic acid methyl ester have been identified (28, 36).Self-inhibitors have been characterized in Puccinia, Uromyces, Colletotrichum, Dictyostelium, Fusarium oxysporum, and Aspergillus and can be volatile or nonvolatile (2,3,16,24,28).They also can influence other fungal processes, for example, mycosporine-alanine produced by Colletotrichum graminic...
Aims: To identify and characterize an antifungal compound produced by Bacillus subtilis YM 10-20 which prevents spore germination of Penicillium roqueforti. Methods and Results: The antifungal compound was isolated by acid precipitation with HCl. This compound inhibited fungal germination and growth. Identification by HPLC and mass spectrometry analysis showed high similarity to iturin A. Permeabilization and morphological changes in P. roqueforti conidia in the presence of the inhibitor were revealed by fluorescence staining and SEM, respectively. Conclusions: The iturin-like compound produced by B. subtilis YM 10-20 permeabilizes fungal spores and blocks germination. Significance and Impact of the Study: Fluorescence staining in combination with flow cytometry and scanning electron microscopy are efficient tools for assessing the action of antifungal compounds against spores. Iturin-like compounds may permeabilize fungal spores and inhibit their germination.
1-Octen-3-ol is a volatile germination self-inhibitor produced by Penicillium paneum that blocks the germination process. The size of conidia treated with 1-octen-3-ol was similar to that of freshly harvested conidia. Exposure to 1-octen-3-ol resulted in staining of 10-20% of the conidia with PI and TOTO, fluorescent DNA probes that cannot enter cells with an intact membrane, whereas only 3-5% of non-treated conidia were stained. Addition of 1-octen-3-ol to germinating conidia resulted in transient dissipation of the pH gradient. From this, we conclude that slight permeabilisation of the fungal membrane occurs in the presence of the inhibitor. Two-dimensional gel electrophoresis analysis of protein patterns revealed striking differences between non-germinated conidia, germinated conidia and 1-octen-3-ol-treated conidia. In conclusion, 1-octen-3-ol has mild effects on the plasma membrane, but interferes with essential metabolic processes, such as swelling and germination of the conidia, but in a reversible manner.
A primeira fase do trabalho objetivou avaliar o efeito do tempo de deslintamento químico, 1:30 e 4:30 min, sobre o nível de infecção de Colletotrichum gossypii inoculado artificialmente em sementes de algodoeiro (Gossypium hirsutum). Sementes de algodoeiro com línter foram inoculadas com C. gossypii, mediante contato das mesmas com colônias do fungo em placas de Petri de 9 cm de diâmetro, por 30 h. Os parâmetros avaliados foram a ocorrência de fungos e o poder germinativo das sementes. Na segunda fase, o objetivo foi avaliar a influência do exsudato de sementes de algodoeiro, em função do tempo da duração do deslintamento com ácido sulfúrico, considerando-se as frações de sedimentação de sementes e diferentes condições de envelhecimento artificial sobre o desenvolvimento de C. gossypii, em condições de laboratório. As sementes foram deslintadas quimicamente com ácido sulfúrico comercial concentrado pelos períodos de 1:30 e 4:30 min, separadas em frações de sedimentação em água e submetidas ao envelhecimento artificial por 0, 72 e 96 h. Os substratos foram obtidos a partir do exsudato resultante da embebição contendo os eletrólitos lixiviados das sementes. O desenvolvimento de C. gossypii na presença do exsudato das sementes foi avaliado em meio agarizado, através da medição do crescimento micelial e da esporulação do fungo. O deslintamento químico, pelo período de 1:30 min, propiciou aumento do percentual de ocorrência de C. gossypii em sementes não-desinfestadas superficialmente, e o crescimento micelial e a esporulação do fungo foram favorecidos pelo substrato proveniente de sementes deslintadas por 4:30 e 1:30 min, respectivamente.
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