Patterns of bacterial biodiversity in the glacial meltwater streams of the McMurdo Dry Valleys, Antarctica

Abstract

Microbial consortia dominate glacial meltwater streams from polar regions, including the McMurdo Dry Valleys (MDV), where they thrive under physiologically stressful conditions. In this study, we examined microbial mat types and sediments found in 12 hydrologically diverse streams to describe the community diversity and composition within and across sites. Sequencing of the 16S rRNA gene from 129 samples revealed ∼24 000 operational taxonomic units (<97% DNA similarity), making streams the most biodiverse habitat in the MDV. Principal coordinate analyses revealed significant but weak clustering by mat type across all streams (ANOSIM R-statistic = 0.28) but stronger clustering within streams (ANOSIM R-statistic from 0.28 to 0.94). Significant relationships (P < 0.05) were found between bacterial diversity and mat ash-free dry mass, suggesting that diversity is related to the hydrologic regimes of the various streams, which are predictive of mat biomass. However, correlations between stream chemistry and community members were weak, possibly reflecting the importance of internal processes and hydrologic conditions. Collectively, these results suggest that localized conditions dictate bacterial community composition of the same mat types and sediments from different streams, and while MDV streams are hotspots of biodiversity in an otherwise depauperate landscape, controls on community structure are complex and site specific.

Keywords: 16S rRNA gene; community structure; cyanobacteria; diversity; microbial mats; polar region.

Figure 1.

Stream sampling sites from Taylor, Wright and Miers Valleys. The presence of the mat types/sediment is indicated in the figure legend (black = black mat, green = green mat, orange = orange mat, red = red mat, and brown = sediment).

Figure 2.

Stacked bar graphs of the OTUs derived from 16S rRNA gene sequences at the phylum level for all bacterial sequences (A), the order level for chemotrophic bacteria (B), and the genus level for Cyanobacteria/chloroplasts (C). The samples are averaged by the identified K-means clusters and are organized by mat/sediment type (black = black mat, green = green mat, orange = orange mat, red = red mat, and brown = sediment). See Fig. S1 for the taxonomic distribution of OTUs for individual samples.

Figure 3.

Stacked bar graphs of the OTUs derived from 18S rRNA gene sequences at the phylum level for all eukaryotes (A) and at the genus level for photosynthetic eukaryotes (B). The samples are organized by mat/sediment type (black = black mat, green = green mat, orange = orange mat, red = red mat, and brown = sediment).

Figure 4.

Principal coordinate analysis (PCoA) of UniFrac weighted distance matrices created from rarefied OTU tables containing all phototrophic and chemotrophic OTUs for all mat samples color coded by lake basin (A) and mat type (B).

Figure 5.

PCoA of UniFrac weighted distance matrices created from rarefied OTU tables for mat and sediment samples within individual streams color coded by mat/sediment type (black = black mat, green = green mat, orange = orange mat, red = red mat, and brown = sediment). Significant ANOSIM clusters are designated by dashed (P < 0.10) or solid (P < 0.05) circles.

Figure 6.

Linear regressions for AFDM and two diversity measures, Chao1 which is a non-parametric lower-bound richness estimator, and phylogenetic diversity (PD) calculated using the Faith Phylogenetic Diversity Metric.

Figure 7.

Heatmap of the correlations between stream chemistry parameters (5 of the 20 possible variables with variance inflation factors under 2.00) and the 30 most abundant Bacteria families excluding Cyanobacteria/chloroplasts (A) and the 15 most abundant Cyanobacteria/chloroplast families (B). Clustering was performed using the ‘dendrogram’ command in the heatmap.2 package in R. Abbreviations are as follows: TotalN, total nitrogen; SRP, soluble reactive phosphorus; TDS, total dissolved solids; DOC, dissolved organic carbon.