Variation with depth of the abundance, diversity and pigmentation of culturable bacteria in a deep ice core from the Yuzhufeng Glacier, Tibetan Plateau

It has been suggested that the cryosphere is a new biome uniquely dominated by microorganisms, although the ecological characteristics of these cold-adapted bacteria are not well understood. We investigated the vertical variation with depth of the proportion of pigmented bacteria recovered from an ice core drilled in the Yuzhufeng Glacier, Tibetan Plateau. A total of 25,449 colonies were obtained from 1250 ice core sections. Colonies grew on only one-third of the inoculated Petri dishes, indicating that although the ice core harbored abundant culturable bacteria, bacteria could not be isolated from every section. Four phyla and 19 genera were obtained; Proteobacteria formed the dominant cluster, followed by Actinobacteria, Bacteroidetes and Firmicutes. The proportion of pigmented bacteria increased with depth from 79 to 95% and yellow-colored colonies predominated throughout the ice core, making up 47% of all the colonies. Pigments including α- and β-carotene, diatoxanthin, peridinin, zea/lutein, butanoyloxy, fucoxanthin and fucoxanthin were detected in representative colonies with α-carotene being the dominant carotenoid. To the best of our knowledge, this is the highest resolution study of culturable bacteria in a deep ice core reported to date.

Changes of the Bacterial Abundance and Communities in Shallow Ice Cores from Dunde and Muztagata Glaciers, Western China

In this study, six bacterial community structures were analyzed from the Dunde ice core (9.5-m-long) using 16S rRNA gene cloning library technology. Compared to the Muztagata mountain ice core (37-m-long), the Dunde ice core has different dominant community structures, with five genus-related groups Blastococcus sp./Propionibacterium, Cryobacterium-related., Flavobacterium sp., Pedobacter sp., and Polaromas sp. that are frequently found in the six tested ice layers from 1990 to 2000. Live and total microbial density patterns were examined and related to the dynamics of physical-chemical parameters, mineral particle concentrations, and stable isotopic ratios in the precipitations collected from both Muztagata and Dunde ice cores. The Muztagata ice core revealed seasonal response patterns for both live and total cell density, with high cell density occurring in the warming spring and summer months indicated by the proxy value of the stable isotopic ratios. Seasonal analysis of live cell density for the Dunde ice core was not successful due to the limitations of sampling resolution. Both ice cores showed that the cell density peaks were frequently associated with high concentrations of particles. A comparison of microbial communities in the Dunde and Muztagata glaciers showed that similar taxonomic members exist in the related ice cores, but the composition of the prevalent genus-related groups is largely different between the two geographically different glaciers. This indicates that the micro-biogeography associated with geographic differences was mainly influenced by a few dominant taxonomic groups.

The dynamic bacterial communities of a melting High Arctic glacier snowpack

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.