Tracking Microcystis N and C Uptake from Urea in Whole Lake Water

Abstract

Lake Erie experiences annual summer cyanobacterial harmful algal blooms (cHABs) dominated by the cyanobacterium, Microcystis. Microcystis species are composed of a wide variety of strains, some of which produce the hepatotoxin microcystin. Lake Erie cHABs result from eutrophication driven primarily by agricultural runoff. About 60% of the world’s nitrogen fertilizer is in the form of urea, which has increased ~100-fold in the last four years. Unlike nitrate and ammonia, which are inorganic sources of nitrogen, urea is an organic source. A previous study found that cultured Microcystis can use both nitrogen and carbon from dual-labeled (15N, 13C) urea. To analyze the potential of carbon and nitrogen uptake from urea in uncultured Western Lake Erie Microcystis, we incubated whole lake water samples with dual-labeled urea. The collection of Microcystis strains sampled from the lake did not incorporate carbon but did incorporate nitrogen. Overall, this work provides further evidence that Microcystis uses urea as a source of nitrogen, but that the use of urea as a carbon source may vary across different Microcystis strains and/or environmental conditions.