Methanotrophic Activity, Abundance, and Diversity in Forested Swamp Pools: Spatiotemporal Dynamics and Influences on Methane Fluxes

Abstract

Methane oxidation (methanotrophy) in the water column and sediments of forested swamp pools likely control seasonal and annual emission of CH4 from these systems, but the methanotrophic microbial communities, their activities, locations, and overall impact, is poorly understood. Several techniques including 14CH4 oxidation assays, culture-based most probable number (MPN) estimates of methane-oxidizing bacteria (MOB) and protozoan abundance, MOB strain isolation and characterization, and PCR techniques were used to investigate methanotrophy at a forested swamp near Ithaca, New York. The greatest methanotrophic activity and largest numbers of MOB occurred predominantly at the low oxygen sediment/water interface in the water column. Seasonally, methanotrophic activity was very dynamic, ranging from 0.1 to 61.9 μ moles CH4 d−1 g−1 dry sediment, and correlated most strongly with dissolved inorganic carbon (r = 0.896). Incorporation of methanotrophic variables (abundance and activity) into existing CH4 flux regression models improved model fit, particularly during mid summer when CH4 fluxes were most dynamic. Annually integrated methane flux and methanotrophic activity measurements indicate that differences in methanotrophic activity at the sediment/water interface likely accounted for differences in the annual CH4 emission from the field site. Direct isolations of MOB resulted in the repeated isolation of organisms most closely related to Methylomonas methanica S1. A single acidophilic, type II MOB related to Methylocella palustris K was also isolated. Using a PCR-based MPN method and 16S rRNA genome copy number from isolates and control strains, type I and type II MOB were enumerated and revealed type I dominance of the sediment-associated MOB community.