Strategies for the growth of fungi under conditions of nitrogen deficiency

Xylotrophic fungi are in the focus of scientists because of their capacity to grow under conditions of marked nitrogen deficiency. Basidiomycetes growing on wood developed some strategies that allow them find and consume nitrogen not easy accessible for many other organisms. In our experiments it was demonstrated that xylotrophic fungi, in contrast to basidiomycetes preferred rich organic substrates, are capable of not only prolonged searching growth (f-growth or forage growth) but also developed specific strategy to life in the wood (x-growth or xylotrophic growth). F-growth is characterized by a predominant use of resources accumulated by fungal mycelium before — that is such kind of growth is limited. X-growth is quite similar to f-growth but it is required additional nitrogen consumption and let the fungus occupy wooden substrates without limitation. Both types of growth are required recycling, but xylotrophic basidiomycetes belonging to different ecological groups use not compatible strategies to get nitrogen. While oyster mushroom could search for the rich nitrogen sources (living micro- and macroorganisms and so on) aphyllophoroids are able to extract of the trace nitrogen and include it in the recycling.Работа выполнена при финансовой поддержке РФФИ (проекты 12–04–00684, 14–04–00864, 15–04–06881) и Программы научного развития МГУ (ПНР–10)

Lomasomes and Other Fungal Plasma Membrane Macroinvaginations Have a Tubular and Lamellar Genesis

The plasma membrane of filamentous fungi forms large-sized invaginations, which are either tubes or parietal vesicles. Vesicular macroinvaginations at the ultrastructural level correspond to classical lomasomes. There is an assumption that vesicular macroinvaginations/lomasomes may be involved in macrovesicular endocytosis. The original aim of this study was to test for the presence of macroendocytosis in xylotrophic basidiomycetes using time-lapse and Z-stacks fluorescent microscopic technologies. However, the results were unexpected since most of the membrane structures labeled by the endocytic tracer (FM4-64 analog) are various types of plasma membrane macroinvaginations and not any endomembranes. All of these macroinvaginations have a tubular or lamellar genesis. Moreover, under specific conditions of a microscopic preparation, the diameter of the tubes forming the macroinvaginations increases with the time of the sample observation. In addition, the morphology and successive formation of the macroinvaginations mimic the endocytic pathway; these invaginations can easily be mistaken for endocytic vesicles, endosomes, and vacuole-lysosomes. The paper analyzes the various macroinvagination types, suggests their biological functions, and discusses some features of fungal endocytosis. This study is a next step toward understanding complex fungal physiology and is a presentation of a new intracellular tubular system in wood-decaying fungi

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

International audienceIn Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3-5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described