Identification of the Functionally Active Methanotroph Population in a Peat Soil Microcosm by Stable-Isotope Probing

Abstract

ABSTRACT The active population of low-affinity methanotrophs in a peat soil microcosm was characterized by stable-isotope probing. “Heavy” 13 C-labeled DNA, produced after microbial growth on 13 CH 4 , was separated from naturally abundant 12 C-DNA by cesium chloride density gradient centrifugation and used as a template for the PCR. Amplification products of 16S rRNA genes and pmoA , mxaF , and mmoX , which encode key enzymes in the CH 4 oxidation pathway, were analyzed. Sequences related to extant type I and type II methanotrophs were identified, indicating that these methanotrophs were active in peat exposed to 8% (vol/vol) CH 4 . The 13 C-DNA libraries also contained clones that were related to β-subclass Proteobacteria , suggesting that novel groups of bacteria may also be involved in CH 4 cycling in this soil.