The dynamic bacterial communities of a melting High Arctic glacier snowpack

Abstract

Snow environments can occupy over a third of land surface area, but little is known about the dynamics of snowpack bacteria. The effect of snow melt on bacterial community structure and diversity of surface environments of a Svalbard glacier was examined using analyses of 16S rRNA genes via T-RFLP, qPCR and 454 pyrosequencing. Distinct community structures were found in different habitat types, with changes over 1 week apparent, in particular for the dominant bacterial class present, Betaproteobacteria. The differences observed were consistent with influences from depositional mode (snowfall vs aeolian dusts), contrasting snow with dust-rich snow layers and near-surface ice. Contrary to that, slush as the decompositional product of snow harboured distinct lineages of bacteria, further implying post-depositional changes in community structure. Taxa affiliated to the betaproteobacterial genus Polaromonas were particularly dynamic, and evidence for the presence of betaproteobacterial ammonia-oxidizing bacteria was uncovered, inviting the prospect that the dynamic bacterial communities associated with snowpacks may be active in supraglacial nitrogen cycling and capable of rapid responses to changes induced by snowmelt. Furthermore the potential of supraglacial snowpack ecosystems to respond to transient yet spatially extensive melting episodes such as that observed across most of Greenland's ice sheet in 2012 merits further investigation.

Figure 1

Study location and design. (a) Overview of the glacier's location. Larsbreen is a High Arctic valley glacier near Longyearbyen, Svalbard (inset). (b) At each sampling station, three snowpits were at the corners of a triangle 10 m apart; snowpack profiles and the range of surface snow, snow and slush habitat thicknesses illustrated. (c) shows the locality of sampling stations 1, 2 and 3, where, triplicate snowpits were excavated as described.

Figure 2

qPCR estimation of mean β-AOB 16S rRNA gene abundance in different habitats; error bars represent ±1 s.e.m.

Figure 3

Barcoded amplicon 454 pyrosequencing of bacterial 16S rRNA genes. (a) Canonical Analysis of Principal Components of UCLUST 97%-clustered OTUs modelled by habitat type (total misclassification error=20% slush: hollow triangles, snow: filled triangles, surface snow: squares, ice: diamonds.) (b) distribution of OTUs aligned and assigned to known bacterial phyla as the cumulative relative abundance of OTUs associated with each phylum. (c) Percentage of OTUs affiliated to known bacterial phyla.

Figure 4

Canonical correspondence analysis model of environmental variable influence on the relative abundance of RDP-aligned OTUs. The variables displayed were retained following stepwise optimization of multicollinearity. Percentage of total variance explained per environmental axis is indicated for both axes. Supplementary Table 4 provides further details.