Geomicrobiology of Eukaryotic Microorganisms

Eukaryotic microbes participate in many biogeochemical cycles, although quantifying their role is not easy, and the discussion below comes generally to only qualitative conclusions. Eukaryotes lack a number of the biogeochemically important functions that are carried out only by archaea (e.g., methanogenesis), bacteria (the anammox chemolithotrophic denitrification reaction), or archaea and bacteria (e.g., chemolithotrophy, diazotrophy, and dissimilatory reduction of sulfate). Microbial eukaryotes have one ancestral attribute, phagotrophy, which adds a novel link to food webs and thus modifies biogeochemical cycles, and have endosymbioses as well as ectosymbioses which can recruit metabolism from archaeans (methanogenesis) and bacteria (chemolithotrophic sulfide oxidation, diazotrophy). The ability of eukaryotes to carry out oxidative phosphorylation and the related respiratory carbonmetabolism, and photosynthesis, as genetically integrated processes is an outcome of bacterial symbioses. The biogeochemical importance of fungi is significant in several key areas. These include organic and inorganic transformations, nutrient and element cycling, rock and mineral transformations, bioweathering, mycogenic mineral formation, fungal-clay interactions, and metal-fungal interactions. Although such transformations can occur in both aquatic and terrestrial habitats, it is in the terrestrial environment where fungi probably have the greatest influence especially when considering soil, rock and mineral surfaces, and the plant root-soil interface. Of special significance are the mutualistic symbioses, lichens and mycorrhizas. Geochemical transformations that take place can influence plant productivity and the mobility and speciation of toxic elements, and are therefore of considerable socioeconomic relevance. Some fungal transformations have beneficial applications in environmental biotechnology, e. g., in metal and radionuclide leaching, recovery and detoxification, and xenobiotic and organic pollutant degradation. They may also result in adverse effects when these processes are associated with the degradation of foodstuffs, natural products and building materials, including wood, stone and concrete.