Coordinated Diel Gene Expression of Cyanobacteria and Their Microbiome

Diel rhythms have been well recognized in cyanobacterial metabolisms. However, whether this programmed activity of cyanobacteria could elicit coordinated diel gene expressions in microorganisms (microbiome) that co-occur with cyanobacteria and how such responses in turn impact cyanobacterial metabolism are unknown. To address these questions, a microcosm experiment was set up using Lake Erie water to compare the metatranscriptomic variations of Microcystis cells alone, the microbiome alone, and these two together (whole water) over two day-night cycles. A total of 1205 Microcystis genes and 4779 microbiome genes exhibited significant diel expression patterns in the whole-water microcosm. However, when Microcystis and the microbiome were separated, only 515 Microcystis genes showed diel expression patterns. A significant structural change was not observed for the microbiome communities between the whole-water and microbiome microcosms. Correlation analyses further showed that diel expressions of carbon, nitrogen, phosphorous, and micronutrient (iron and vitamin B₁₂) metabolizing genes were significantly coordinated between Microcystis and the microbiome in the whole-water microcosm. Our results suggest that diel fluxes of organic carbon and vitamin B₁₂ (cobalamin) in Microcystis could cause the diel expression of microbiome genes. Meanwhile, the microbiome communities may support the growth of Microcystis by supplying them with recycled nutrients, but compete with Microcystis for iron.