Matthew J. Wooller John W. Pohlman Catharine Catranis John Quensen James M. Tiedje Mary Beth Leigh Ruo He 2012 Arctic lakes are a significant source of the greenhouse gas methane (CH₄), but the role that methane oxidizing bacteria (methanotrophs) play in limiting the overall CH₄ flux is poorly understood. Here, we used stable isotope probing (SIP) techniques to identify the metabolically active aerobic methanotrophs in upper sediments (0&ndash;1 cm) from an arctic lake in northern Alaska sampled during ice-free summer conditions. The highest CH₄ oxidation potential was observed in the upper sediment (0&ndash;1 cm depth) with 1.59 &mu;mol g wet weight^-1 day^-1 compared with the deeper sediment samples (1&ndash;3 cm, 3&ndash;5 cm and 5&ndash;10 cm), which exhibited CH₄ oxidation potentials below 0.4 &mu;mol g wet weight^-1 day^-1. Both type I and type II methanotrophs were directly detected in the upper sediment total communities using targeted primer sets based on 16S rRNA genes. Sequencing of 16S rRNA genes and functional genes (<i>pmoA</i> and <i>mxaF</i>) in the ¹³C-DNA from the upper sediment indicated that type I methanotrophs, mainly Methylobacter, Methylosoma, Methylomonas and Methylovulum miyakonense, dominated the assimilation of CH₄. Methylotrophs, including the genera Methylophilus and/or Methylotenera, were also abundant in the ¹³CDNA. Our results show that a diverse microbial consortium acquired carbon from CH₄ in the sediments of this arctic lake. application/pdf 10.1111/j.1462-2920.2012.02725.x en Wiley Identification of functionally active aerobic methanotrophs in sediments from an arctic lake using stable isotope probing article