Geomicrobiology of the carbon, nitrogen and sulphur cycles in Powell Lake: a permanently stratified water column containing ancient seawater

Abstract

Summary We present the first geomicrobiological characterization of the meromictic water column of Powell Lake (British Columbia, Canada), a former fjord, which has been stably stratified since the last glacial period. Its deepest layers (300–350 m) retain isolated, relict seawater from that period. Fine‐scale vertical profiling of the water chemistry and microbial communities allowed subdivision of the water column into distinct geomicrobiological zones. These zones were further characterized by phylogenetic and functional marker genes from amplicon and shotgun metagenome sequencing. Binning of metagenomic reads allowed the linkage of function to specific taxonomic groups. Statistical analyses (analysis of similarities, Bray–Curtis similarity) confirmed that the microbial community structure followed closely the geochemical zonation. Yet, our characterization of the genetic potential relevant to carbon, nitrogen and sulphur cycling of each zone revealed unexpected features, including potential for facultative anaerobic methylotrophy, nitrogen fixation despite high ammonium concentrations and potential micro‐aerobic nitrifiers within the chemocline. At the oxic–suboxic interface, facultative anaerobic potential was found in the widespread freshwater lineage acI (Actinobacteria), suggesting intriguing ecophysiological similarities to the marine SAR11. Evolutionary divergent lineages among diverse phyla were identified in the ancient seawater zone and may indicate novel adaptations to this unusual environment.

Bacterial, Phytoplankton, and Viral Distributions and Their Biogeochemical Contexts in Meromictic Lake Cadagno Offer Insights into the Proterozoic Ocean Microbial Loop

“…6). The increases in genotypic and phenotypic alpha diversity in the lower chemocline and monimolimnion were consistent with previous 16S rRNA genebased studies of Lake Cadagno (33) and other permanently stratified systems, including Powell Lake (45), Ursu Lake (46), and Fara Fund Lake (46). Given the evidence that in microbial ecology "diversity begets diversity" (47), the observed increase in substrate diversity in the lower chemocline and monimolimnion (Fig.…”

Draft Metagenome-Assembled Genomes from Methane-Rich Echo Lake, Montana

“…The presence of microbes related to Chlorobium , Methylotenera , and Rhodoferax within Echo Lake is consistent with communities in other old, stratified lakes in which sulfur cycling and methylotrophy is prevalent ( 17 ). The genome related to the genus Methylovulum contains both particulate and soluble methane monooxygenase genes; this suggests that this genus is a major contributor to the steep methane chemocline and plays a vital role in regulating methane efflux from Echo Lake.…”

Depth-discrete metagenomics reveals the roles of microbes in biogeochemical cycling in the tropical freshwater Lake Tanganyika

“…Much remains to be learnt about microbial biodiversity inhabiting lakes’ hypolimnions and deep lakes worldwide. With few microbial ecology studies focused on lake hypolimnions 16–19 , we cannot speculate if microbes in the hypolimnion of Lake Tanganyika are truly endemic. Nevertheless, we note the contrast between typical freshwater microbes dominating the epilimnion, and the high prominence of Archaea and CP, including Candidate Phyla Radiation (CPR) in the anoxic zones.…”