Northern lakes are ice-covered for a large part of the year, yet our understanding of microbial diversity and activity during winter lags behind that of the ice-free period. In this study, we investigated under-ice diversity and metabolism of Verrucomicrobia in seasonally ice-covered lakes in temperate and boreal regions of Quebec, Canada using 16S rRNA sequencing, metagenomics and metatranscriptomics. Verrucomicrobia, particularly the V1, V3 and V4 subdivisions, were abundant during ice-covered periods. A diversity of Verrucomicrobia genomes were reconstructed from Quebec lake metagenomes. Several genomes were associated with the ice-covered period and were represented in winter metatranscriptomes, supporting the notion that Verrucomicrobia are metabolically active under ice. Verrucomicrobia transcriptome analysis revealed a range of metabolisms potentially occurring under ice, including carbohydrate degradation, glycolate utilization, scavenging of chlorophyll degradation products, and urea use. Genes for aerobic sulfur and hydrogen oxidation were expressed, suggesting chemolithotrophy may be an adaptation to conditions where labile carbon may be limited. The expression of genes for flagella biosynthesis and chemotaxis was detected, suggesting Verrucomicrobia may be actively sensing and responding to winter nutrient pulses, such as phytoplankton blooms. These results increase our understanding on the diversity and metabolic processes occurring under ice in northern lakes ecosystems.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.

1Northern lakes are ice-covered for a large part of the year, yet our understanding 2 of microbial diversity and activity during winter lags behind that of the ice-free period. In 3 this study, we investigated under-ice diversity and metabolism of Verrucomicrobia in 4 seasonally ice-covered lakes in temperate and boreal regions of Quebec, Canada using 5 16S rRNA sequencing, metagenomics and metatranscriptomics. Verrucomicrobia, 6 particularly the V1, V3 and V4 subdivisions, were abundant during ice-covered periods. 7A diversity of Verrucomicrobia genomes were reconstructed from Quebec lake 8 metagenomes. Several genomes were associated with the ice-covered period and were 9represented in winter metatranscriptomes, supporting the notion that Verrucomicrobia are 10 metabolically active under ice. Verrucomicrobia transcriptome analysis revealed a range 11 of metabolisms potentially occurring under ice, including carbohydrate degradation, 12 glycolate utilization, scavenging of chlorophyll degradation products, and urea use. 13Genes for aerobic sulfur and hydrogen oxidation were expressed, suggesting 14 chemolithotrophy may be an adaptation to conditions where labile carbon may be limited. 15The expression of genes for flagella biosynthesis and chemotaxis was detected, 16suggesting Verrucomicrobia may be actively sensing and responding to winter nutrient 17 pulses, such as phytoplankton blooms. These results increase our understanding on the 18 diversity and metabolic processes occurring under ice in northern lakes ecosystems. 19This study demonstrates the importance of studying the ice-covered period in the face of 33 climate change and should spur future year-round investigations on microbial community 34 structure and function in ice-covered freshwater ecosystems. 35 36 37 4 Hampton, 2016;Hampton et al., 2017). To better understand the contribution of winter 60 communities to lake metabolism and nutrient cycling, year-round investigation of the 61 metabolic traits and activities of freshwater microorganisms is warranted. 62