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Little is known regarding the temporal and spatial functional variation of freshwater bacterial community (BC) under non-bloom conditions, especially in winter. To address this, we used metatranscriptomics to assess bacterial gene transcription variation among three sites across three seasons. Our metatranscriptome data for freshwater BCs at three public beaches (Ontario, Canada) sampled in the winter (no ice), summer and fall (2019) showed relatively little spatial, but a strong temporal variation. Our data showed high transcriptional activity in summer and fall but surprisingly, 89% of the KEGG pathway genes and 60% of the selected candidate genes (52 genes) associated with physiological and ecological activity were still active in freezing temperatures (winter). Our data also supported the possibility of an adaptively flexible gene expression response of the freshwater BC to low temperature conditions (winter). Only 32% of the bacterial genera detected in the samples were active, indicating that the majority of detected taxa were non-active (dormant). We also identified high seasonal variation in the abundance and activity of taxa associated with health risks (i.e., Cyanobacteria and waterborne bacterial pathogens). This study provides a baseline for further characterization of freshwater BCs, health-related microbial activity/dormancy and the main drivers of their functional variation (such as rapid human-induced environmental change and climate change)., Competing Interests: Declaration of competing interest Authors declare no competing interest., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The aquatic bacterial community (BC) plays a vital role in determining the nature and rate of ecosystem function. However, the biotic and abiotic factors influencing BC structure and function are largely unknown. Hence, the current study characterizes the impact of biotic and abiotic factors on aquatic bacterial biodiversity to determine whether the dominant effects are biotic or abiotic by partitioning their relative effects across temperate Canadian lakes. We collected water samples from sixty southern Ontario lakes and characterized their BC and microbial eukaryotic community (MEC) compositions using high throughput metabarcode sequencing of 16S and 18S rRNA gene fragments. The diversity and richness of aquatic BCs differed considerably among our study lakes, and those differences were explained by environmental, spatial, and biotic (MEC) factors (31%, 23%, and 23% of variance explained, respectively). The relatively large contribution from biotic and abiotic factors (54%), relative to spatial effects, shows deterministic processes prevail in shaping BC assembly in freshwater lakes. However, spatial effects also contributed significantly, highlighting the role of stochastic processes (ecological drift and coupled with limited dispersal) in shaping BC structure. Furthermore, our co-occurrence network analysis showed strong positive and negative interactions within and between the BCs and MECs, indicating mutualistic or antagonistic co-occurrence patterns relationships play important roles in driving the variation in BC composition among our sampled lakes. Considered together, our community analyses show that deterministic and stochastic processes combined contribute to determining the aquatic BC composition, and hence likely function as well, across a broad array of temperate freshwater lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)