Cell-specific nitrogen uptake by natural cyanobacterial harmful algal bloom communities in Lake Erie

Each summer western Lake Erie experiences an annual cyanobacterial harmful algal bloom (cyanoHAB), often dominated by the non-diazotrophic and toxigenic cyanobacteria species, Microcystis. The annual phosphorus (P) load has a well-established role in determining the overall bloom size each year, but nitrogen (N) availability is also important as it likely influences the production of the N-rich toxin microcystin, as well as the population dynamics of toxic and non-toxic Microcystis strains. Both the dominant form of N (organic vs. inorganic) and the cyanobacterial strain composition shift as the bloom progresses, as does the composition of the heterotrophic bacterial communities associated with Microcystis colonies. Recent metagenomics and culture-based work suggests that some of these heterotrophs may be involved in N acquisition and cycling processes with Microcystis. In this study we examined the relative N uptake of both Microcystis and heterotrophic bacteria in natural bloom communities during the 2021 Lake Erie CyanoHAB. We used nano-secondary ion mass spectrometry (nano-SIMS) complemented with shotgun metagenomic community data, to measure N incorporation of three substrates (nitrate, ammonia, and urea) at single cell resolution during early, peak, and late bloom phases. Results show that the amount of N assimilated by Microcystis and heterotrophic bacteria varies between substrates and bloom stage, and provide insight into the role of heterotrophs in N assimilation by CyanoHAB bloom communities.

Primary Presenter: Jenan Kharbush, University of Michigan (jenanjk@umich.edu)

Authors:

Jenan Kharbush, University of Michigan  (jenanjk@umich.edu)

Hadley Vande Vusse, University of Michigan  (hadvusse@umich.edu)

Wei Li, Lawrence Livermore National Laboratory  (li81@llnl.gov)

Xavier Mayali, Lawrence Livermore National Laboratory  (mayali1@llnl.gov)

E. Anders Kiledal, University of Michigan  (kiledal@umich.edu)

Sara Rivera, University of Michigan  (sarariv@umich.edu)

Megan Keene, University of Michigan  (mekeene@umich.edu)

Mallory Armstrong, University of Michigan  (malarmst@umich.edu)