Molecular analysis of microorganisms has lead to a rapid increase in information about prokaryotic diversity but the microbial eukaryotes of ecosystems have been less thoroughly examined.  In freshwaters, microbial eukaryotes play important roles in ecosystem function as primary producers and as grazers linking primary production to higher trophic levels. Despite these crucial roles, molecular investigations of eukaryotes in freshwaters are rare compared to those of bacteria and archaea.  Consequently there is lack of genetic information to align with taxonomic and functional descriptions of even the most abundant freshwater microbial eukaryotes.  In collaboration with Linda Amaral Zettler (MBL), and as part of the MIRADA project, we recently analyzed microbial community composition in a suite of north temperate lakes using 454 tag sequencing of ribosomal RNA genes. An analysis of this data revealed that among the ten most abundant microbial eukaryotes, only five could be identified to taxonomic family, and none to genus or species. Whereas in the same samples, six of the ten most abundant bacteria were identified to genus. This demonstrates the serious lack of knowledge about genetic diversity of freshwater microbial eukaryotes.

I am investigating biogeochemical drivers of spatial and temporal variability in microbial eukaryotic community composition. Microbial eukaryotic communities are separated by lake as well as lake depth in stratified lakes, similar to what has been shown for bacterial communities (Kent et al. 2007, Shade et al. 2008). In addition, microbial eukaryotic communities do not follow identical distributions annually, but the types of organisms observed across years is similar. Despite the observation that algal communities folllow seasonal trajectories (Kent et al. 2007), this is not observed for the entire eukaryotic community. Therefore, other, non-seasonal factors must regulate microbial eukaryotic community composition as a whole. Few biogeochemical parameters follow strict seasonal trends. I am currently comparing trends in community variation with biogeochemistry to elucidate its role in structuring microbial eukaryotic populations.

References

Shade, A., S.E.Jones, K.D. McMahon. The influence of habitat heterogeneity on bacterial community composition and dynamics. 2008.  Environmental Microbiology. 10:1057-1067.

Kent A.D., C. Yannarell, J.A. Rusak, E.W. Triplett, and K.D. McMahon. 2007. Synchrony in aquatic microbial community dynamics. The ISME Journal 1:38-47