title: Anaerobic Fungi: A Potential Source of Biological H2 in the Oceanic Crust.
abstract: The recent recognition of fungi in the oceanic igneous crust challenges the understanding of this environment as being exclusively prokaryotic and forces reconsiderations of the ecology of the deep biosphere. Anoxic provinces in the igneous crust are abundant and increase with age and depth of the crust. The presence of anaerobic fungi in deep-sea sediments and on the seafloor introduces a type of organism with attributes of geobiological significance not previously accounted for. Anaerobic fungi are best known from the rumen of herbivores where they produce molecular hydrogen, which in turn stimulates the growth of methanogens. The symbiotic cooperation between anaerobic fungi and methanogens in the rumen enhance the metabolic rate and growth of both. Methanogens and other hydrogen-consuming anaerobic archaea are known from subseafloor basalt; however, the abiotic production of hydrogen is questioned to be sufficient to support such communities. Alternatively, biologically produced hydrogen could serve as a continuous source. Here, we propose anaerobic fungi as a source of bioavailable hydrogen in the oceanic crust, and a close interplay between anaerobic fungi and hydrogen-driven prokaryotes.
authors.affiliation: Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History Stockholm, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Ivarsson
authors.affiliation: Department of Microbiology, Uppsala BioCenter, Swedish University of Agricultural Sciences Uppsala, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Schnürer
authors.affiliation: Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History Stockholm, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bengtson
authors.affiliation: Department of Geological Sciences, Stockholm University Stockholm, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Neubeck
keywords: anaerobic fungi; chemoautotrophs; deep biosphere; fungal interactions; ocean crust