Metagenomics-informed community structure of photoautotrophs in meromictic Green Lake

Green Lake is an euxinic, meromictic lake producing unique sulfur and carbon cycling. Its bacterial community includes sulfur oxidizers, photosynthetic green and purple sulfur bacteria, and cyanobacteria capable of both oxygenic and anoxygenic photosynthesis, previously described using 16S rDNA sequencing in the context of its geochemistry. Here, we couple community 18S and 16S rDNA and geochemistry with concurrent metagenomics and 16S rRNA sequencing.  The mixolimnion prokaryotic phototrophs were a mix cyanobacteria, primarily Synechococcus, transitioning to Chlorobium and Chromatium below the chemocline with increasing sulfide concentrations. Other anoxygenic photosynthetic capable cyanobacterial taxa included Phormidium, Leptolyngbya, and Oscillatoria. Eukaryotic phototrophs included gymnodinian dinoflagellates, restricted to the surface, and cryptomonads throughout the mixolimnion. Many cryptomonad taxa have demonstrated sulfide tolerance and migration into sulfide rich layers in other lakes, which may explain the disparate distribution. The Synechococcus assembled genome included sqr genes which enable sulfide detoxification and anoxygenic photosynthesis. The Synechococcus persisted below the increase in sulfide, but decreased abruptly, corresponding to changes in cyanobacterial phage abundance. Green Lake photosynthesis was dominated by sulfide tolerant eukaryotes and cyanobacteria, and sulfide mediated anoxygenic photosynthesis, further detailing our understanding of sulfur and carbon cycling in euxinic, meromictic lakes.

Primary Presenter: William Edwards, Niagara University (wje@niagara.edu)

Authors:

William Edwards, Niagara University  (wje@niagara.edu)

Grace Sweeney, Niagara University  (gsweeney@mail.niagara.edu)

Cassandra Marnocha, Niagara University  (cmarnocha@niagara.edu)