Shotgun metagenomes from productive lakes in an urban region of Sweden.

Urban lakes provide multiple benefits to society while influencing life quality. Moreover, lakes and their microbiomes are sentinels of anthropogenic impact and can be used for natural resource management and planning. Here, we release original metagenomic data from several well-characterized and anthropogenically impacted eutrophic lakes in the vicinity of Stockholm (Sweden). Our goal was to collect representative microbial community samples and use shotgun sequencing to provide a broad view on microbial diversity of productive urban lakes. Our dataset has an emphasis on Lake Mälaren as a major drinking water reservoir under anthropogenic impact. This dataset includes short-read sequence data and metagenome assemblies from each of 17 samples collected from eutrophic lakes near the greater Stockholm area. We used genome-resolved metagenomics and obtained 2378 metagenome assembled genomes that de-replicated into 514 species representative genomes. This dataset adds new datapoints to previously sequenced lakes and it includes the first sequenced set of metagenomes from Lake Mälaren. Our dataset serves as a baseline for future monitoring of drinking water reservoirs and urban lakes.

Linking prokaryotic genome size variation to metabolic potential and environment.

While theories and models have appeared to explain genome size as a result of evolutionary processes, little work has shown that genome sizes carry ecological signatures. Our work delves into the ecological implications of microbial genome size variation in benthic and pelagic habitats across environmental gradients of the brackish Baltic Sea. While depth is significantly associated with genome size in benthic and pelagic brackish metagenomes, salinity is only correlated to genome size in benthic metagenomes. Overall, we confirm that prokaryotic genome sizes in Baltic sediments (3.47 Mbp) are significantly bigger than in the water column (2.96 Mbp). While benthic genomes have a higher number of functions than pelagic genomes, the smallest genomes coded for a higher number of module steps per Mbp for most of the functions irrespective of their environment. Some examples of this functions are amino acid metabolism and central carbohydrate metabolism. However, we observed that nitrogen metabolism was almost absent in pelagic genomes and was mostly present in benthic genomes. Finally, we also show that Bacteria inhabiting Baltic sediments and water column not only differ in taxonomy, but also in their metabolic potential, such as the Wood-Ljungdahl pathway or the presence of different hydrogenases. Our work shows how microbial genome size is linked to abiotic factors in the environment, metabolic potential and taxonomic identity of Bacteria and Archaea within aquatic ecosystems.

Microbial functional genes are driven by gradients in sediment stoichiometry, oxygen, and salinity across the Baltic benthic ecosystem.

BACKGROUND: Microorganisms in the seafloor use a wide range of metabolic processes, which are coupled to the presence of functional genes within their genomes. Aquatic environments are heterogenous and often characterized by natural physiochemical gradients that structure these microbial communities potentially changing the diversity of functional genes and its associated metabolic processes. In this study, we investigated spatial variability and how environmental variables structure the diversity and composition of benthic functional genes and metabolic pathways across various fundamental environmental gradients. We analyzed metagenomic data from sediment samples, measured related abiotic data (e.g., salinity, oxygen and carbon content), covering 59 stations spanning 1,145 km across the Baltic Sea. RESULTS: The composition of genes and microbial communities were mainly structured by salinity plus oxygen, and the carbon to nitrogen (C:N) ratio for specific metabolic pathways related to nutrient transport and carbon metabolism. Multivariate analyses indicated that the compositional change in functional genes was more prominent across environmental gradients compared to changes in microbial taxonomy even at genus level, and indicate functional diversity adaptation to local environments. Oxygen deficient areas (i.e., dead zones) were more different in gene composition when compared to oxic sediments. CONCLUSIONS: This study highlights how benthic functional genes are structured over spatial distances and by environmental gradients and resource availability, and suggests that changes in, e.g., oxygenation, salinity, and carbon plus nitrogen content will influence functional metabolic pathways in benthic habitats. Video Abstract.

A Genomic Perspective Across Earth's Microbiomes Reveals That Genome Size in Archaea and Bacteria Is Linked to Ecosystem Type and Trophic Strategy.

Our view of genome size in Archaea and Bacteria has remained skewed as the data has been dominated by genomes of microorganisms that have been cultivated under laboratory settings. However, the continuous effort to catalog Earth's microbiomes, specifically propelled by recent extensive work on uncultivated microorganisms, provides an opportunity to revise our perspective on genome size distribution. We present a meta-analysis that includes 26,101 representative genomes from 3 published genomic databases; metagenomic assembled genomes (MAGs) from GEMs and stratfreshDB, and isolates from GTDB. Aquatic and host-associated microbial genomes present on average the smallest estimated genome sizes (3.1 and 3.0 Mbp, respectively). These are followed by terrestrial microbial genomes (average 3.7 Mbp), and genomes from isolated microorganisms (average 4.3 Mbp). On the one hand, aquatic and host-associated ecosystems present smaller genomes sizes in genera of phyla with genome sizes above 3 Mbp. On the other hand, estimated genome size in phyla with genomes under 3 Mbp showed no difference between ecosystems. Moreover, we observed that when using 95% average nucleotide identity (ANI) as an estimator for genetic units, only 3% of MAGs cluster together with genomes from isolated microorganisms. Although there are potential methodological limitations when assembling and binning MAGs, we found that in genome clusters containing both environmental MAGs and isolate genomes, MAGs were estimated only an average 3.7% smaller than isolate genomes. Even when assembly and binning methods introduce biases, estimated genome size of MAGs and isolates are very similar. Finally, to better understand the ecological drivers of genome size, we discuss on the known and the overlooked factors that influence genome size in different ecosystems, phylogenetic groups, and trophic strategies.