Ecogenomics of microbes in stratified water columns with a history of mixing disturbance

Many freshwater lakes thermally stratify seasonally. Darkly stained bog lakes have especially steep thermal and biogeochemical gradients during the summer, with high oxygen demand driving highly reducing conditions in the hypolimnion. Microbial communities stratify vertically to position themselves at optimal depths based on their lifestyles. This structure can be disrupted by physical water column mixing. Here we describe a dataset spanning 5 years in three humic bog lakes. One is polymictic, one is usually dimictic, and the third is dimictic but was artificially mixed in 2008. Metagenomic sequencing was used to study the community composition and functional potential across the time series. Green sulfur bacteria in the genus Chlorobium were abundant in the two dimitic lakes, but were absent from the polymictic lake. Organisms capable of extracellular electron transfer co-occurred with the Chlorobium, pointing to cryptic cycling of electron carriers in the water. Both the species composition and population-level genetic variation were distinct among the three lakes and thermal layers. These findings shed light on the organisms responsible for biogeochemical cycling in these lakes, which are analogs for boreal lakes with high rates of carbon burial.

Primary Presenter: Katherine Mcmahon, University of Wisconsin-Madison (trina.mcmahon@wisc.edu)

Authors:

Katherine McMahon, University of Wisconsin  (trina.mcmahon@wisc.edu)