Nitrogen-obtaining and -conserving strategies in xylotrophic basidiomycetes

ABSTRACT

Nitrogen in sufficient quantities is strictly necessary for all living organisms. In this study, the ability of some xylotrophic basidiomycetes to grow extremely long on a solid growth medium full of carbon nutrition but lacking a nitrogen source in its composition was discovered. The nitrogen oligotrophy of wood-decaying fungi is associated with their adaptation to live in a wood substrate, which is also deficient in nitrogen content. This nitrogen-depleted cultural growth is called “pseudo-foraging” and can be used as a simplified model of wood-decaying growth. Four main nitrogen-obtaining and -conserving strategies (nitrogen concentration, using alternative sources of nitrogen, economy of growth, and nutritional recycling), which are attributed to wood-colonizing xylotrophs in the literature, were revised studying the pseudo-foraging model. Based on the results, some aspects of the behavior of xylotrophs deep in undecomposed wood were predicted. For example, one of the results is that for pseudo-foraging xylotrophs, the main way to obtain nitrogen is its concentration in their mycelium from the nutrient medium in which nitrogen is contained in the impurities of the components of the medium. The result suggests that in bulk solid wood, the nitrogen concentration strategy also dominates the strategy of using diazotrophic and other alternative nitrogen. In addition, three individual unprecedented mechanisms, which supposedly help the xylotrophic fungi to colonize wood in nature (generation of fine mycelium, macrovesicular endocytosis, formation and conversion of super-elongated mitochondria), were investigated in the laboratory.

KEYWORDS:

• BAM15
• fine mycelium
• foraging growth
• hybrid growth
• macrovesicular endocytosis
• nitrogen fixation
• nonyl acridine orange
• pseudo-foraging growth
• rhodamine 6G
• super-elongated mitochondria
• wood-decaying fungi

ACKNOWLEDGMENTS

The authors dedicate this work to the memory of the prominent mycologist and phytopathologist, Prof. Yu. T. Dyakov, teacher and friend.

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Funding

This study was funded by Russian Foundation for Basic Research (research project no. 18-04-00266 А) and conducted within the framework of the State Assignment contracts 0112-2019-0002 (VIGG RAS) and АAAА-А16-116021660088-9 (MSU, part 2, section 01 10 336). The Moscow University Development Program (UDP-10) provided part of the equipment for this study.