Investigating the Spatial and Temporal Variations in Methanotroph Population in “Pulsing” Wetlands by Stable Isotope Probing.

Quantitative information about methanotroph community dynamics can yield critical information about which factors regulate competition between Type I and Type II methanotrophs in nature. Stable isotopic probing using ¹³C-CH₄ offers the tool to track methane-derived carbon (C) uptake by methanotrophs and the fate of the C in soil and microbial pool. However, the huge diversity and complexity of the methanotrophs have constrained the use of ¹³C-phospholipid fatty acid (PLFA) compared to pure-culture based studies.  Therefore, the objective of this study was to determine the effectiveness of the ¹³C-PLFA method in characterizing spatial and temporal dynamics of Type I and II methanotrophs and thereby, elucidate the flow paths of ¹³C-CH₄. Soil samples were collected from the permanently flooded site of two “pulsing” wetlands located at the Olentangy River Wetland Research Park, Columbus, Ohio. Soil samples incubated with ¹³C-CH₄ showed strong labeling of Type I (containing 16:1 PLFA) and Type II (containing 18:1 PLFA) methanotroph groups. The relative abundances of the two groups reflect in situ conditions in small, difficult-to-probe spatial niches where methanotrophs are active in flooded soils. Label was incorporated in the PLFAs 16:1ɷ7c, 16:1ɷ5c, and to a lesser extent into 16:1ɷ6c in the soil samples. Labeling patterns in soil changed under the higher (60-100 ppmv) CH₄ mixing ratio compared to the lower ratio of 2-30 ppmv. Label also appeared in 18:0 and 18:1ɷ9c in addition to the Type II biomarker 18:1ɷ8c. This study provides critical information on the fate of ¹³C in soil microbial pool during methanotrophy.