Fungi in freshwaters: ecology, physiology and biochemical potential

Abstract

Research on freshwater fungi has concentrated on their role in plant litter decomposition in streams. Higher fungi dominate over bacteria in terms of biomass, production and enzymatic substrate degradation. Microscopy-based studies suggest the prevalence of aquatic hyphomycetes, characterized by tetraradiate or sigmoid spores. Molecular studies have consistently demonstrated the presence of other fungal groups, whose contributions to decomposition are largely unknown. Molecular methods will allow quantification of these and other microorganisms. The ability of aquatic hyphomycetes to withstand or mitigate anthropogenic stresses is becoming increasingly important. Metal avoidance and tolerance in freshwater fungi implicate a sophisticated network of mechanisms involving external and intracellular detoxification. Examining adaptive responses under metal stress will unravel the dynamics of biochemical processes and their ecological consequences. Freshwater fungi can metabolize organic xenobiotics. For many such compounds, terrestrial fungal activity is characterized by cometabolic biotransformations involving initial attack by intracellular and extracellular oxidative enzymes, further metabolization of the primary oxidation products via conjugate formation and a considerable versatility as to the range of metabolized pollutants. The same capabilities occur in freshwater fungi. This suggests a largely ignored role of these organisms in attenuating pollutant loads in freshwaters and their potential use in environmental biotechnology.

Tar-spot infection delays fungal colonization and decomposition of maple leaves

“…Aquatic hyphomycetes are regarded as the main fungal drivers of leaf decomposition in streams (Krauss et al 2011), and maximum spore release from recovered leaves usually is correlated with decay rate (Gessner and Chauvet 1994, Maharning and Bä rlocher 1996. We have insufficient data for a comparative analysis, but the trend among the 3 disk types supports the notion that aquatic hyphomycetes are important decomposers.…”

Changes in dominance among species in aquatic hyphomycete assemblages do not affect litter decomposition rates

“…Identification of species contributions to total fungal biomass in microcosm experiments could, however, be achieved with molecular techniques (e.g. realtime PCR) (Krauss et al 2011). Also, the substitution of the conidial suspension with sterile nutrient solution every 3 d might have affected the assemblage structure.…”

High habitat-specificity in fungal communities in oligo-mesotrophic, temperate Lake Stechlin (North-East Germany)

“…The low diversity of aquatic compared to terrestrial (e.g., soil) fungi partly results from the fact that mycological studies in aquatic systems remain rare. Apart from a few well studied lotic ecosystems and wetlands (Wong et al 1998;Shearer et al 2007;Gulis et al 2009;Krauss et al 2011), the total diversity of aquatic fungi has not been linked to habitat heterogeneity. Most studies in freshwaters have focussed on marshlands (reviewed in Kuehn 2008) and examined the open water, leaf litter or emergent macrophytes (e.g., Typha, Phragmites).…”