Diversity and Assembling Processes of Bacterial Communities in Cryoconite Holes of a Karakoram Glacier

Abstract

Cryoconite holes are small ponds that form on the surface of glaciers that contain a dark debris, the cryoconite, at the bottom and host active ecological communities. Differences in the structure of bacterial communities have been documented among Arctic and mountain glaciers, and among glaciers in different areas of the world. In this study, we investigated the structure of bacterial communities of cryoconite holes of Baltoro Glacier, a large (62 km in length and 524 km of surface) glacier of the Karakoram, by high-throughput sequencing of the V5-V6 hypervariable regions of the 16S rRNA gene. We found that Betaproteobacteria dominated bacterial communities, with large abundance of genera Polaromonas, probably thanks to its highly versatile metabolism, and Limnohabitans, which may have been favoured by the presence of supraglacial lakes in the area where cryoconite holes were sampled. Variation in bacterial communities among different sampling areas of the glacier could be explained by divergent selective processes driven by variation in environmental conditions, particularly pH, which was the only environmental variable that significantly affected the structure of bacterial communities. This variability may be due to both temporal and spatial patterns of variation in environmental conditions.

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

“…Their relative abundance can markedly vary among geographical areas; for instance, on the Rotmoosferner Glacier (Austria), Proteobacteria were more abundant than on Forni, while Bacteroidetes were more scarce (Edwards and others, 2013). On the Baltoro Glacier (Pakistani Karakoram), the most abundant orders were Burkholderiales, Enterobacteriales and Sphingobacteriales (Ambrosini and others, 2017). Finally, Cameron and others (2012) showed that cryoconite bacterial communities varied according to their geographical location on a global scale.…”

“…Cryoconite holes range in diameter from few centimetres to more than a metre and host the most metabolically active ecological communities in glacier ecosystems (Laybourn-Parry and others, 2012). These microhabitats host bacteria, tardigrades, rotifers, collembola, algae, viruses and nematodes (Hodson and others, 2008; Cook and others, 2016a, b) and have been studied on glaciers in different geographical areas, such as the Alps (Edwards and others, 2013; Franzetti and others, 2017a), Arctic (Gokul and others, 2016), Greenland (Uetake and others, 2016), Antarctica (Cameron and others, 2012), Himalaya (Takeuchi and others, 2000) and Karakoram (Ambrosini and others, 2017). Bacterial communities of cryoconite holes seem to vary according to ecological conditions of the holes, particularly with their size and pH (Ambrosini and others, 2017), sediment thickness and organic matter content (Telling and others, 2012) and the hydrology of the glacier surface (Edwards and others, 2011), as well as their location within a glacier (Stibal and others, 2015).…”

“…Bacterial communities of cryoconite holes seem dominated by Cyanobacteria, Actinobacteria, Proteobacteria and Bacteroidetes on both polar and temperate glaciers (Musilova and others, 2015; Ambrosini and others, 2017; Gokul and others, 2016; Franzetti and others, 2017a). However, most of the studies conducted so far investigated cryoconite bacterial populations by snapshot sampling, probably because of logistic limitations to the sampling design, and almost neglected the temporal variability of the ecological communities of cryoconite holes (e.g.…”

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.…”

Variation in the nitrous oxide reductase gene (nosZ)-denitrifying bacterial community in different primary succession stages in the Hailuogou Glacier retreat area, China

“…However, heterotrophic colonizers, decomposing organic material, are also important in the initial establishment of functional communities (Hodkinson et al, 2003). Previous studies in this field have mainly focused on the diversity and composition of the soil microbial community in the primary succession of receding glaciers (Ambrosini et al, 2017;Fernández-Martínez et al, 2017). Only a few studies have employed molecular tools to understand the diversity and composition of the functional microbial community along the forelands of receding glaciers (Kandeler et al, 2006;Töwe et al, 2010).…”