Ecology of aquatic hyphomycetes and the role of biodiversity

Andreas Bruder
Laboratory of Applied Microbiology, University of Applied Sciences and Arts of Southern Switzerland (SUPSI).

Aquatic hyphomycetes (or Ingoldian fungi) represent a polyphyletic group of microscopic fungi, which have their main habitat in well-oxygenated streams, mainly headwaters. The group is dominated by ascomycetes with a minority of basidiomycetes and widely distributed in most biomes worldwide. As almost exclusive saprotrophs, principal ecological roles of aquatic hyphomycetes center on the decomposition of allochthonous plant litter, which is dominated by abscised leaves from the riparian vegetation surrounding streams. For most food webs of headwater streams, allochthonous leaf litter is the main resource since primary production is limited by shading from the riparian vegetation. Most species of aquatic hyphomycetes have the enzymatic capacity to degrade refractory compounds of leaves, including lignin and hemicellulose, but also more labile polysaccharides. Nevertheless, the activity of aquatic hyphomycetes depends on litter quality, i.e. it often correlates positively with litter nutrient concentrations but negatively with concentrations of lignin and polyphenols. Headwater stream ecosystems are important in terms of their abundance and ubiquity and because of their disproportionally high biodiversity. However, the biodiversity of microbes including fungi is vastly understudied. Due to their position at the deepest point in the landscape and the various services they provide for human societies, stream ecosystems are also among the most threatened and impacted by human activities. Human uses of the land and the water modify habitat availability and physical and chemical water quality, results in pollution and facilitates species invasions. As a consequence, biodiversity of freshwaters has been declining rapidly during the past decades, probably faster than in most other ecosystem types. These changes warrant enquiries into the consequences of biodiversity loss on stream ecosystem functioning in general and on detrital food webs in particular. As the main goal of my seminar, I will take the opportunity to highlight the role of aquatic hyphomycetes in stream ecosystems. I will present and discuss examples of the role of biodiversity gradients on the activity of aquatic hyphomycetes. These examples will be drawn from recent field- and laboratory experiments. Due to the intimate connection and the importance of the processes, I will also provide examples on the influence of diversity of resources, i.e. of leaf litter on fungal activity. Some studies suggest that not only interspecific diversity but also intraspecific diversity of aquatic hyphomycetes may influence their sensitivity to environmental stressors and their performance when decomposing leaf litter. Detailed studies addressing these research questions require quantification of intraspecific diversity, which, however, is challenging at best with established approaches in fungal taxonomy (i.e. morphological identification and DNA barcoding). The final part of my seminar will be dedicated to a novel proteomic approach that we are developing based on MALDI TOF mass spectrometry and which is addressing this challenge. Due to the broad range of ribosomal proteins analyzed simultaneously, this technique provides vast genomic information. It thus lends itself for detailed characterization and identification of cultures and for quantification of inter- and intraspecific diversity.

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