Microbial eukaryotes play critical roles in the MCM ecosystems as the major primary producers at the base of the food webs through top predators. Our new focus on microbial eukaryotes contributes to addressing all 4 of our working hypotheses and are a critical part of several new and ongoing experiments (LICE, tLICE, SLIME).
Lakes - We hypothesized that owing to lake-specific biogeochemical signatures, microbial eukaryote diversity and function in the water columns would be distinct across the MCM lakes. Next generation sequencing of 18S rRNA from the water columns of Lakes Bonney and Fryxell revealed that microbial eukaryote communities are distinct between the photic zone of the lakes as well as the aphotic anoxic layers of the water column (Fig. 1). Lake Bonney (east and west lobe) eukaryote communities are dominated by chlorophytes as well as mixotrophic algae (cryptophytes, haptophytes) and several heterotrophic protists (choanoflagellates, dinoflagellates, Ochrophyta). In contrast, a cryptophyte related to an Antarctic marine mixotroph, Gemingera cryophila, dominates the photic zone of Lake Fryxell (Fig. 1). In addition, microbial eukaryote community structure in the oxic zones of the east and west lobes of Lake Bonney was distinct from Lake Fryxell, and communities were also sorted based on the presence/absence of oxygen.
As the microbial eukaryotes contribute the vast majority of new carbon in the MDV lake ecosystems, we also hypothesized that microbial eukaryote community structure would be linked with the occurrence of heterotrophic bacteria. To test this hypothesis, we investigated co-occurrence patterns between eukaryotes and prokaryotes across the water columns of Lakes Bonney and Fryxell. We identified four eukaryote OTUs which were positively correlated with 14 bacterial OTUs.
Soils - Microbial eukaryotes, and heterotrophic soil protists in particular play important roles in MCM ecosystem functioning. Preliminary studies are beginning to reveal their patterns of biodiversity and soil food webs.
Streams and aeolian material - Because the distinctive silica frustules of diatoms are well preserved in sediments, fossil diatom preserved in lake sediments are useful tracers for the origins of accumulated materials, as was done for a sediment core from Lake Fryxell (Konfirst et al 2011). Using a similar approach, we have studied diatoms present in the aeolian material collected at different locations in the MDV to understand meta-community dynamics. Aeolian transport is an important dispersal vector for microorganisms in the MDV and could play a role in community assembly. While the diatoms in the aeolian samples are sparse in terms of concentration, most (over 85%) of the diatom species that have been described for the MDV overall were found in 17 samples of aeolian material from 7 different sites in the MDV. An even more compelling result was that a number of intact diatom cells with chloroplasts were found, which indicate viability. A meta-analysis of the diatom records for the MDV, shows that the aeolian diatom communities lie between the communities found in the streams and those found in the lakes and ponds. This result suggests that Aeolian materials derived from the abundant cyanobacterial mats in the streams may seed these communities found in cryoconite holes, lakes and ponds.