Comparison of carbon metabolism dynamics between Lake Michigan coastal and offshore bacterial communities as assessed through metatranscriptomics

Despite their small share of Earth’s surface, freshwater ecosystems contribute significantly to regional and global carbon budgets. Bacterial communities in these ecosystems play a fundamental role in the biogeochemistry and food web dynamics. In this study, we characterized the spatiotemporal patterns in bacterial dissolved organic carbon (DOC) metabolism in Lake Michigan, one of the largest lakes in the world. Using metatranscriptomics, we investigated bacterial community gene expression across a nearshore-to-offshore transect in the lake during spring and summer seasons in 2017-2018. Comparison of transcript abundance for gene families between nearshore and offshore bacterioplankton highlighted differential expression for several genes between the two regions. Notably, genes involved in the uptake and metabolism of various DOC substrates such as amino acids and sugars were over-expressed in the offshore bacterial communities as compared to nearshore. A more detailed analysis of all the transporter genes expressed for DOC substrates revealed similar trends – a higher overall expression of DOC transporter genes in the offshore versus nearshore. These results imply that the offshore bacterial communities in Lake Michigan are more carbon limited than in nearshore and are likely spending more metabolic energy in acquiring various DOC substrates. Overall, this study provides molecular ecology-based evidence of the current oligotrophic conditions in offshore Lake Michigan, and identifies the DOC compounds that contribute to carbon flux in this valuable freshwater resource.

Primary Presenter: Adit Chaudhary, Rush University (adit.chaudhary89@gmail.com)

Authors:

Adit Chaudhary, Rush University  (adit.chaudhary89@gmail.com)

Rachel Poretsky, University of Illinois at Chicago  (microbe@uic.edu)