Potential sources of bacteria colonizing the cryoconite of an Alpine glacier

Abstract

We investigated the potential contribution of ice-marginal environments to the microbial communities of cryoconite holes, small depressions filled with meltwater that form on the surface of Forni Glacier (Italian Alps). Cryoconite holes are considered the most biologically active environments on glaciers. Bacteria can colonize these environments by short-range transport from ice-marginal environments or by long-range transport from distant areas. We used high throughput DNA sequencing to identify Operational Taxonomic Units (OTUs) present in cryoconite holes and three ice-marginal environments, the moraines, the glacier forefield, and a large (> 3 m high) ice-cored dirt cone occurring on the glacier surface. Bacterial communities of cryoconite holes were different from those of ice-marginal environments and hosted fewer OTUs. However, a network analysis revealed that the cryoconite holes shared more OTUs with the moraines and the dirt cone than with the glacier forefield. Ice-marginal environments may therefore act as sources of bacteria for cryoconite holes, but differences in environmental conditions limit the number of bacterial strains that may survive in them. At the same time, cryoconite holes host a few OTUs that were not found in any ice-marginal environment we sampled, thus suggesting that some bacterial populations are positively selected by the specific environmental conditions of the cryoconite holes.

Water bears dominated cryoconite hole ecosystems: densities, habitat preferences and physiological adaptations of Tardigrada on an alpine glacier

“…The most biologically active part of glacial ecosystems is the supraglacial zone (the surface of glaciers), where during summer the interaction of psychrophilic bacteria and algae along with mostly wind-blown dust form a layer of cryoconite (named from Greek 'kryos'-cold, 'konis'-dust) and influence the darkening of ice and the melting of water-filled reservoirs called cryoconite holes (Wharton et al 1985;Takeuchi et al 2000;Hodson et al 2008;Cook et al 2016). Cryoconite holes host unique assemblages mostly of bacteria, algae and microfauna different from the ones found in ice-free areas (Stibal et al 2015;Franzetti et al 2017;Ambrosini et al 2017;Liu et al 2017;Zawierucha et al 2018a, b). These specific reservoirs constitute glacial biodiversity hot spots and bioreactors responsible for organic matter production and also play an important role in glacier mass balance, glacial geochemistry, carbon cycling and as a storage of various pollutants (Mueller et al 2001;Fountain et al 2004;Bagshaw et al 2007;Stibal et al 2010;Pittino et al 2018;Łokas et al 2018;Zawierucha et al 2018aZawierucha et al , 2019a.…”

“…The ecology and biology of cryoconite holes on Forni have been the subject of intensive studies with the majority of recent works focusing on the diversity, ecology and metabolism of bacteria (Franzetti et al 2016(Franzetti et al , 2017Ferrario et al 2017;Pittino et al 2018). Franzetti et al (2017) showed that moraines may act as sources of bacteria for cryoconite holes on Forni, but different conditions limit them, and at the same time, holes are inhabited by unique bacterial strains known only from glaciers. Comparably, tardigrades from tundra and Arctic cryoconite holes show unique assemblages of animals on glaciers (Zawierucha et al 2016).…”

Bacterial communities of cryoconite holes of a temperate alpine glacier show both seasonal trends and year-to-year variability

“…This suggested that communities in new holes can be seeded by those present in previous holes melted away by ablation and that ecological succession of cryoconite bacterial communities continues throughout the ablation season, independently of the time when a hole forms (Franzetti and others, 2017a). Cryoconite communities, however, are seeded also by inputs from near glacier environments (Telling and others, 2012; Stibal and others, 2015; Franzetti and others, 2017b) and possibly by bacteria subjected to long-range transport (Cook and others, 2016a, b) or deposited by precipitations (R.S. Azzoni, personal communication).…”

Disappearing Kilimanjaro snow—Are we the last generation to explore equatorial glacier biodiversity?

“…However, as on glaciers of polar, alpine and third pole regions, scientists should expect more species of metazoans on and in the vicinity of equatorial glaciers, together with novel species of primary producers and bacteria. Glaciers worldwide as supraglacial ecosystems encompass habitats like streams, lakes, cryoconite holes (water‐filled reservoirs on glacier surfaces), weathering crusts, glacier mice (moss balls), dirt cones, and tills (Cook et al, ; Coulson & Midgley, ; Franzetti et al, ; Hodson et al, ; Zawierucha, Buda, et al, ; Figure ). Parts of equatorial glaciers covered by perennial snow also may constitute viable habitats based on recently discovered distinct and isolated biogeographic communities on snow in various parts of the world (Kuja et al, ; Lutz et al, ; Onuma et al, ).…”