Samad Md Sainur, Bertilsson Stefan
Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala UniversityUppsala, Sweden; Department of Microbiology and Immunology, University of OtagoDunedin, New Zealand.
Department of Ecology and Genetics, Limnology and Science for Life Laboratory, Uppsala University Uppsala, Sweden.
Front Microbiol. 2017 Feb 3;8:142. doi: 10.3389/fmicb.2017.00142. eCollection 2017.
Lakes are significant sources of methane (CH) to the atmosphere. Within these systems, methanotrophs consume CH and 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 CH explained 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 CH and methanotrophs, which was possibly due to usage of CH. Methanotrophs were present at concentrations ranging from 10 to 10 copies/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 of genes in two clone libraries from two of the ice-covered lakes (Ekoln and Ramsen) separated the methanotrophs into five distinct clusters of sp. (Type I). Terminal restriction fragment length polymorphism analysis of the gene 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.
湖泊是大气中甲烷（CH）的重要来源。在这些系统中，甲烷氧化菌消耗CH，并作为一种潜在的生物过滤器减轻这种强效温室气体的排放。然而，环境参数的时空变化如何影响湖泊中甲烷氧化菌的丰度、多样性和群落结构，目前仍未得到很好的理解。为了填补这一知识空白，我们在冬季（冰封期）和夏季从瑞典五个不同湖泊的三个深度（表层、中层和底层）采集了水样，这些深度代表了从有氧到亚氧或缺氧区域。通过定量实时聚合酶链反应测定甲烷氧化菌的丰度，并与环境变量进行比较，结果表明温度、季节以及深度、磷酸盐浓度、溶解氧和CH解释了观察到的甲烷氧化菌丰度变化。由于甲烷浓度差异极小（夏季和冬季分别为0.19和0.29 μM），CH与甲烷氧化菌之间仅观察到微弱甚至负相关，这可能是由于CH的消耗所致。在湖泊的整个有氧（表层）和亚氧/缺氧（底层）水体中，甲烷氧化菌的浓度范围为10至10拷贝/升，但在总微生物群落中的占比始终低于1.3%。冬季甲烷氧化菌的相对丰度显著高于夏季，并且在湖泊中随深度持续增加。对来自两个冰封湖泊（埃科尔恩湖和拉姆森湖）的两个克隆文库中的基因进行系统发育分析，将甲烷氧化菌分为五个不同的 sp.（I型）簇。对基因的末端限制性片段长度多态性分析进一步揭示了湖泊之间以及冬季和夏季之间甲烷营养群落的显著差异，而水层之间没有显著差异。该研究为低甲烷双季湖淡水甲烷氧化菌的多样性、丰度、群落组成以及时空分布提供了新的见解。
