title: Seasonal Variation in Abundance and Diversity of Bacterial Methanotrophs in Five Temperate Lakes.
abstract: Lakes are significant sources of methane (CH4) to the atmosphere. Within these systems, methanotrophs consume CH4and act as a potential biofilter mitigating the emission of this potent greenhouse gas. However, it is still not well understood how spatial and temporal variation in environmental parameters influence the abundance, diversity, and community structure of methanotrophs in lakes. To address this gap in knowledge, we collected water samples from three depths (surface, middle, and bottom) representing oxic to suboxic or anoxic zones of five different Swedish lakes in winter (ice-covered) and summer. Methanotroph abundance was determined by quantitative real time polymerase chain reaction and a comparison to environmental variables showed that temperature, season as well as depth, phosphate concentration, dissolved oxygen, and CH4explained the observed variation in methanotroph abundance. Due to minimal differences in methane concentrations (0.19 and 0.29 μM for summer and winter, respectively), only a weak and even negative correlation was observed between CH4and methanotrophs, which was possibly due to usage of CH4. Methanotrophs were present at concentrations ranging from 105to 106copies/l throughout the oxic (surface) and suboxic/anoxic (bottom) water mass of the lakes, but always contributed less than 1.3% to the total microbial community. Relative methanotroph abundance was significantly higher in winter than in summer and consistently increased with depth in the lakes. Phylogenetic analysis ofpmoAgenes in two clone libraries from two of the ice-covered lakes (Ekoln and Ramsen) separated the methanotrophs into five distinct clusters ofMethylobactersp. (Type I). Terminal restriction fragment length polymorphism analysis of thepmoAgene further revealed significant differences in methanotrophic communities between lakes as well as between winter and summer while there were no significant differences between water layers. The study provides new insights into diversity, abundance, community composition and spatial as well as temporal distribution of freshwater methanotrophs in low-methane dimictic lakes.
authors.affiliation: Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala UniversityUppsala, Sweden; Department of Microbiology and Immunology, University of OtagoDunedin, New Zealand.
authors.forename: Md Sainur
authors.initials: MS
authors.lastname: Samad
authors.affiliation: Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University Uppsala, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bertilsson
keywords: T-RFLP; ice cover; lakes; methane; methanotrophs; pmoA; qPCR