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 performed to assess the genomic characteristics of methanotrophs in Lovojärvi and the 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 clusters of orthologous groups (COG) categories L (replication, recombination and repair) and S (function unknown) were relatively high in metagenome-assembled genomes representing Methylococcales clearly thriving below the oxic-anoxic interface, suggesting genetic adaptations for increased stress tolerance enabling living in the hypoxic/anoxic conditions. By 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.

中文翻译：

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氧气分层的北方湖泊水柱中甲烷营养生物的垂直分层模式及其遗传控制因子

摘要

在氧分层湖泊的水柱中，对甲烷营养群落的垂直结构及其遗传控制因子的研究仍然不足。因此，我们使用16S rRNA基因测序研究了两个北方湖泊，库瓦贾尔维湖和洛沃贾尔维湖的甲烷营养生物的垂直分层模式。此外，进行了宏基因组分析，以评估Lovojärvi和先前研究过的AlinenMustajärvi湖中甲烷菌的基因组特征。甲烷营养菌群落沿氧梯度垂直构造。Alphaproteobacterial甲烷营养优选好氧水层，而Methylococcales由推定的新属和种组成的甲烷营养生物，特别是在有氧-缺氧界面及其以下，兴旺发达，并表现出明显的深度变化模式，这不能通过其分类学分类完全预测。相反，甲基球菌甲烷营养菌之间的基因组差异解释了它们可变的垂直深度模式。在代表甲基球菌的超基因组组装基因组中，直系同源族（COG）的L（复制，重组和修复）和S（功能未知）类簇中的基因相对较高。明显地在有氧-缺氧的界面之下兴旺，这表明遗传适应可以增加耐压性，从而使生活在低氧/缺氧条件下成为可能。相比之下，COG类别N（细胞运动性）中的基因在氧化-缺氧界面上旺盛的甲基球菌的元基因组组装基因组中相对较高，这表明在垂直波动的氧化-缺氧界面上的遗传适应性增加。