Occurrence of “Ca. Methylopumilus” and OM43 in metagenomic samples; (A) Metagenomic read recruitment (coverage per Gb at 95% identity) of “Ca. M. rimovensis,” “Ca. M. planktonicus,” and “Ca. M. universalis" in epi- and hypolimnetic samples of 13 central European lakes of different trophic states and seasonal samples of the Římov reservoir from 2015 to 2019. Different seasons are color-coded at the top. Mean values for each species are shown, and the full dataset can be found in Table S3; E: Epilimnion (5 m depth); H: Hypolimnion (variable depths, see Table S1); (B) coverage per Gb boxplots of individual species in epi- and hypolimnetic samples. Boxes indicate the 25th and 75th quantiles, medians are displayed by central lines, whiskers indicate the 5th and 95th quantiles, outliers are displayed by open circles; significant differences are displayed as asterisks (*P < .05; ** P < .01; ***P < .001); Mrim: “Ca. M. rimovensis”; Mpla: “Ca. M. planktonicus”; Muni: “Ca. M. universalis"; (C) coverage per Gb boxplots of individual species in oligo-, meso-, and eutrophic lakes. Trophic states are color-coded as in (A) and significant differences are displayed as asterisks as in (B); (D) Spearman correlations between metagenomic recruitment values and environmental factors across the 13 central European lakes and the Římov reservoir; significant differences are displayed as asterisks as in (B); Temp: water temperature (°C); Chla: chlorophyll a concentrations (μg l⁻¹); Cond: conductivity (μS cm⁻¹); DOC: dissolved organic carbon concentrations (mg l⁻¹); NO₃: nitrate concentrations (mg l⁻¹); Green: chlorophyll a concentrations of green algae (μg l⁻¹); Bluegreen: chlorophyll a concentrations of cyanobacteria (μg l⁻¹); Diat: chlorophyll a concentrations of diatoms (μg l⁻¹); Crypt: chlorophyll a concentrations of cryptophytes (μg l⁻¹); (E) metagenomic read recruitment (coverage per Gb at 95% identity) of OM43-a, b, c, and d in samples of the Arctic Ocean and the Delaware Bay estuary.