Biofilms on glacial surfaces: hotspots for biological activity.

Heidi J Smith,Amber Schmit,Sten Littman,Marcel Mm Kuypers,Rachel Foster,Christine M Foreman

doi:10.1038/npjbiofilms.2016.8

Abstract

Glaciers are important constituents in the Earth’s hydrological and carbon cycles, with predicted warming leading to increases in glacial melt and the transport of nutrients to adjacent and downstream aquatic ecosystems. Microbial activity on glacial surfaces has been linked to the biological darkening of cryoconite particles, affecting albedo and increased melt. This phenomenon, however, has only been demonstrated for alpine glaciers and the Greenland Ice Sheet, excluding Antarctica. In this study, we show via confocal laser scanning microscopy that microbial communities on glacial surfaces in Antarctica persist in biofilms. Overall, ~35% of the cryoconite sediment surfaces were covered by biofilm. Nanoscale scale secondary ion mass spectrometry measured significant enrichment of 13C and 15N above background in both Bacteroidetes and filamentous cyanobacteria (i.e., Oscillatoria) when incubated in the presence of 13C–NaHCO3 and 15NH4. This transfer of newly synthesised organic compounds was dependent on the distance of heterotrophic Bacteroidetes from filamentous Oscillatoria. We conclude that the spatial organisation within these biofilms promotes efficient transfer and cycling of nutrients. Further, these results support the hypothesis that biofilm formation leads to the accumulation of organic matter on cryoconite minerals, which could influence the surface albedo of glaciers.

Highlights

Glaciers cover roughly 10% of Earth’s land surface
We propose that the biofilm matrix is integral to biological activity in cryoconite holes through enhanced nutrient storage, cell adhesion and the promotion of efficient nutrient transfer between community members
A diverse microbial community associated with these particles was determined from 454 pyrosequencing to be dominated by Cyanobacteria (27%), Actinobacteria (24%), Proteobacteria (22%) and Bacteroidetes (19%; Supplementary Table S1)

Summary

Introduction

Glaciers cover roughly 10% of Earth’s land surface. As the Earth warms, losses in glacial mass will lead to an export of freshwater to marine ecosystems and a rise in sea level. The photoautotrophic cyanobacteria were further identified by epifluorescent microscopy to be Oscillatoria, the dominant cyanobacterial genus present in cryoconite holes globally.[8] To further explore interactions between auto- and heterotrophic organisms, Bacteroidetes were selected as they have been shown to be a dominant heterotrophic lineage (87%) within Antarctic cryoconite particles.[9] Phylum-specific fluorescent in situ hybridisation probes targeting Bacteroidetes enabled the visualisation of cells within the Oscillatoria phycosphere biofilm (Supplementary Figure S3).

Results

Conclusion