METAGENOMICS AND METATRANSCRIPTOMICS REVEAL CYANOTOXINS AS “STOPPERS” IN THE NITROGEN CYCLE

We studied 20 lakes in the southcentral USA located across a strong precipitation gradient to understand better the relationships between hydraulic flushing, nutrient loading, cyanobacteria composition and activity, the presence and expression of cellular processes related to nitrogen and phosphorus, and the presence and activity of production pathways for multiple cyanotoxins. Using metagenomics and metatranscriptomics, we found that toxin-producing cyanobacteria and toxin-production pathways were more prevalent when hydraulic flushing and loading of total phosphorus and soluble reactive phosphorus were lower. We also found that NO_X loading was associated with toxin-production pathways. Regarding the nitrogen cycle, we discovered that toxin-producing genes were negatively associated with denitrification and dissimilatory nitrate reduction and mostly negatively associated with nitrogen fixation. These same genes were positively associated with nitrification. As a whole, our findings suggest that during periods of drought, exacerbated by climate change in this region, the prevalence of toxin-producing cyanobacteria will increase and that the nitrogen cycle will be disrupted in a way that N₂ gas exchanges with the atmosphere will be reduced, and in-lake nitrogen will accumulate. Furthermore, this nitrogen will accumulate as NO₃, not NH₄. Accumulation of nitrogen in these lakes will likely increase the ambient N:P, destabilizing cyanobacteria blooms that form when N:P is low and reinforcing cyanobacteria blooms that form when N:P is high. This also suggests that in the southcentral USA, climate change will make more pressing the issue of regulating nitrogen and phosphorus loading in managing cyanobacteria blooms.

Presentation Preference: Oral

Primary Presenter: Daniel Roelke, Texas A&M University Galveston (droelke@tamu.edu)

Authors:

Daniel Roelke, Texas A&M University  (droelke@tamu.edu)

Crista Kieley, Texas A&M University  (ckieley@tamu.edu)

Smita Pal, Texas A&M University  (smita30@tamug.edu)

Hagen Klobusnik, University of Connecticut  (hagen.klobusnik@uconn.edu)

Jordan Walker, University of Miami  (jordan.walker@miami.edu)

Sierra Cagle, Texas A&M University  (sec1414@tamug.edu)

Jessica Labonté, Texas A&M University  (labontej@tamug.edu)