Vertical stratification patterns of methanotrophs and their genetic controllers in water columns of oxygen-stratified boreal lakes

Antti J Rissanen, Taija Saarela, Helena Jäntti, Moritz Buck, Sari Peura, Sanni L Aalto, Anne Ojala, Jukka Pumpanen, Marja Tiirola, Marcus Elvert, Hannu Nykänen

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Abstract

The vertical structuring of methanotrophic communities and its genetic controllers remain understudied in the water columns of oxygen-stratified lakes. Therefore, we used 16S rRNA gene sequencing to study the vertical stratification patterns of methanotrophs in two boreal lakes, Lake Kuivajärvi and Lake Lovojärvi. Furthermore, metagenomic analyses were done to assess the genomic characteristics of methanotrophs in Lovojärvi and a previously studied Lake Alinen Mustajärvi. The methanotroph communities were vertically structured along the oxygen gradient. Alphaproteobacterial methanotrophs preferred oxic water layers, while Methylococcales methanotrophs, consisting of putative novel genera and species, thrived especially at and below the oxic-anoxic interface and showed distinct depth variation patterns, which were not completely predictable by their taxonomic classification. Instead, genomic differences among Methylococcales methanotrophs explained their variable vertical depth patterns. Genes in COG categories L (Replication, recombination and repair) and S (Function unknown) were relatively high in metagenome-assembled-genomes representing Methylococcales thriving clearly below the oxic-anoxic interface, suggesting genetic adaptations for increased stress tolerance enabling living in the hypoxic/anoxic conditions. In contrast, genes in COG category N (Cell motility) were relatively high in metagenome-assembled-genomes of Methylococcales thriving at the oxic-anoxic interface, which suggests genetic adaptations for increased motility at the vertically fluctuating oxic-anoxic interface.

Original languageEnglish
Article numberfiaa252
Number of pages16
JournalFEMS Microbiology Ecology
Volume97
Issue number2
Early online date14 Dec 2020
DOIs
Publication statusPublished - 2021
Publication typeA1 Journal article-refereed

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