Abstract
The production of H2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H2-production, of which anaerobic fungi have been put forward as a potential source of H2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H2. A biological origin of the H2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H2 by micro-eukaryotes is an unrecognized source of H2 in hydrothermal systems that may support communities of H2-dependent prokaryotes.
Highlights
Hydrothermal systems are recognized as environments of remarkable microbiological diversity and abundance [1]
We suggest fungi as producers of H2 in subseafloor hydrothermal environments, the evaluation of the quantities and their geobiological impact remains
Mineralogy and fluid inclusions are primarily studied on samples from the sediment-hosted veins
Summary
Hydrothermal systems are recognized as environments of remarkable microbiological diversity and abundance [1]. Deeper in the underlying rocks, our knowledge of the eukaryotic abundance and diversity is still poor. Fungi are so far the only eukaryotes that have been isolated from subseafloor basalts [6]. A recently discovered fossil record in subseafloor crust indicates that fungi are, abundant and widely distributed spatially, and with depth and age [7,8,9]. The presence of fungi in such deep and remote environments raises questions regarding their metabolism and ecological role [8,10,11]. Fungi are known from other environments, like soils, to play a crucial role in biogeochemical cycles and symbiotic relationships with other organisms [12,13]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have