Growth and Metabolism of Fungi in an Atmosphere of Nitrogen

Optimizing Conditions of a Cell-Free Toxic Filtrate Stem Cutting Assay to Evaluate Soybean Genotype Responses to Fusarium Species that Cause Sudden Death Syndrome

Cell-free toxic culture filtrates from Fusarium virguliforme, the causal fungus of soybean sudden death syndrome (SDS), cause foliar symptoms on soybean stem cuttings similar to those obtained from root inoculations in whole plants and those observed in production fields. The objectives of this study were to (i) optimize the production conditions for F. virguliforme cell-free toxic culture filtrates and the incubation conditions of the stem cutting assay used to test the toxicity of the cell-free toxic culture filtrates, and (ii) use the optimized assay and a whole plant root inoculation assay to compare four SDS-causing isolates on a panel of selected soybean genotypes. Area under the disease progress curve (AUDPC) values were highest (P = 0.05) when cuttings were immersed in culture filtrate of fungus grown in soybean dextrose broth, in filtrate produced from the fungus grown for 18 or 22 days, and when stem cuttings were incubated at 30°C. AUDPC values and shoot dry weights from the whole plant root inoculations and the AUDPC values from the stem cutting assay differed (P < 0.05) among nine soybean genotypes tested with F. virguliforme and F. tucumaniae isolates, and the AUDPC values from the two assays were positively correlated (r = 0.44 at P < 0.0001).

Hypoxia and fungal pathogenesis: to air or not to air?

Over the last 3 decades, the frequency of life-threatening human fungal infections has increased as advances in medical therapies, solid-organ and hematopoietic stem cell transplantations, an increasing geriatric population, and HIV infections have resulted in significant rises in susceptible patient populations. Although significant advances have been made in understanding how fungi cause disease, the dynamic microenvironments encountered by fungi during infection and the mechanisms by which they adapt to these microenvironments are not fully understood. As inhibiting and preventing in vivo fungal growth are main goals of antifungal therapies, understanding in vivo fungal metabolism in these host microenvironments is critical for the improvement of existing therapies or the design of new approaches. In this minireview, we focus on the emerging appreciation that pathogenic fungi like Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus are exposed to oxygen-limited or hypoxic microenvironments during fungal pathogenesis. The implications of these in vivo hypoxic microenvironments for fungal metabolism and pathogenesis are discussed with an aim toward understanding the potential impact of hypoxia on invasive fungal infection outcomes.

[The influence of atmospheric gases on growth and toxin production of sterigmatocystin-and patulin-producing molds (author's transl)]

The influence of one-and two-sided regulated atmospheres with lower 02-and increased CO2-concentrations in comparison with air was studied on the growth and toxin-production of 4 different mycotoxin-producing molds (A. versicolor, P. expansum, P. urticae, B. nivea). Low O2-values in the atmosphere (2-0.5%) had scarely an influence on the development and toxinproduction in different nutrient media after 14 d at 25 degrees C. Only higher CO2-and lower O2-concentrations than that of the air (e.g. 40% CO2, 6% O2) reduced the sterigmatocystin-and patulin-production in nearly all cultures, whereas growth was only retarded insignificantly. Atmospheres with 90% CO2 and 10% air as well nitrogen atmospheres with 10% CO2 inhibited remarkably the growth of molds and prevented the toxin-production of nearly all strains. In pure N2-atmospheres most of the A. versicolor strains exhibited growth with toxic mycelia whereas only minimum growth of the patulin-producing species without any patulin synthesis had been observed.