Microbial diversity in arctic freshwaters is structured by inoculation of microbes from soils

Abstract

Microbes are transported in hydrological networks through many environments, but the nature and dynamics of underlying microbial metacommunities and the impact of downslope inoculation on patterns of microbial diversity across landscapes are unknown. Pyrosequencing of small subunit ribosomal RNA gene hypervariable regions to characterize microbial communities along a hydrological continuum in arctic tundra showed a pattern of decreasing diversity downslope, with highest species richness in soil waters and headwater streams, and lowest richness in lake water. In a downstream lake, 58% and 43% of the bacterial and archaeal taxa, respectively, were also detected in diverse upslope communities, including most of the numerically dominant lake taxa. In contrast, only 18% of microbial eukaryotic taxa in the lake were detected upslope. We suggest that patterns of diversity in surface waters are structured by initial inoculation from microbial reservoirs in soils followed by a species-sorting process during downslope dispersal of both common and rare microbial taxa. Our results suggest that, unlike for metazoans, a substantial portion of bacterial and archaeal diversity in surface freshwaters may originate in complex soil environments.

Diversity and abundance of microbial eukaryotes in stream sediments from Svalbard

“…1) and it is possible that it could be influenced by exogenous eukarya transported or deposited by the snow. Similarities were observed between Sample L and a cobble-bottomed headwater stream on the North Slope of Alaska which also drains an unglaciated area underlain by continuous permafrost (Crump et al 2012). Similar to Sample L (Fig.…”

“…High abundances of Ciliophora were observed in porewater near Toolik Lake (40%, Crump et al 2012) and high relative abundances (>45%) of the superphylum Alveolata have additionally been reported in permafrost soil samples (Mackelprang et al 2011;Tveit et al 2013;Jansson and Taş 2014) and glacial meltwater (Luo et al 2009). The relative proportion of Ciliophora in a sample inferred from 18S-rRNA gene sequencing can be greater than their actual abundance since genomes can encode for multiple copies of this gene (Gong et al 2013).…”

“…3). Chlorophytes, which are phototrophic algae, also formed a minor component of a glacial meltwater sample from Svalbard (8%, Luo et al 2009) and an Alaskan headwater stream sample (5%, Crump et al 2012). The presence of Bacillariophyta (diatoms) in sample L may reflect the lower suspended sediment concentrations of the unglaciated stream, compared to the stream draining the glaciated catchment (Fig.…”

“…However, there have been comparatively fewer studies conducted on microbial eukaryotes in cold, highlatitude ecosystems despite the potentially important role that they have in nutrient cycling in these environments. The few cold high-latitude terrestrial ecosystems where microbial eukaryotes have been investigated (Table 1) have focussed on their diversity in glacial cryoconite habitats (Christner et al 2003;Cameron et al 2012;Hamilton et al 2013), freshwater cyanobacterial mats (Jungblut et al 2012) permafrost soils (Coolen et al 2011;Mackelprang et al 2011;Tveit et al 2013Tveit et al , 2014Geisen et al 2015), snow (Harding et al 2011;Hamilton et al 2013;Cameron et al 2015), streams and porewaters (Luo et al 2009;Crump et al 2012), and subglacial environments (Hamilton et al 2013). One of the most abundant phyla found in highlatitude environments are Ciliophora (Tveit et al 2013;Geisen et al 2015) and their presence may control the abundance of bacteria and recycling of soil organic matter (Coolen et al 2011).…”

Determining indicator taxa across spatial and seasonal gradients in the Columbia River coastal margin

“…Biogeography of aquatic microbial communities has been well described across spatial and seasonal scales (Gilbert et al, 2009;Galand et al, 2010;Kirchman et al, 2010;Crump et al, 2012;Fortunato et al, 2012), and although most studies discuss changes in community composition and structure, little is known about the specific taxa that distinguish one community from another. In one long-term study of the English Channel, Gilbert et al (2012) showed strong repeatable seasonal patterns in the general bacterioplankton community and in specific taxonomic groups, and found that seasonal variability was influenced by length of day, temperature, nutrients, and photosynthetically active radiation, rather than biomass of zooplankton species.…”