The active methanotrophic community in hydromorphic soils changes in response to changing methane concentration

Abstract

Methanotrophic communities were studied in several periodically water-saturated gleyic soils. When sampled, each soil had an oxic upper layer and consumed methane from the atmosphere (at 1.75 ppmv). In most gleyic soils the K(m(app)) values for methane were between 70 and 800 ppmv. These are higher than most values observed in dry upland soils, but lower than those measured in wetlands. Based on cultivation-independent retrieval of the pmoA-gene and quantification of partial pmoA gene sequences, type II (Alphaproteobacteria) methanotrophs of the genus Methylocystis spp. were abundant (> 10(7) pmoA target molecules per gram of dry soil). Type I (Gammaproteobacteria) methanotrophs related to the genera Methylobacter and Methylocaldum/Methylococcus were detected in some soils. Six pmoA sequence types not closely related to sequences from cultivated methanotrophs were detected as well, indicating that diverse uncultivated methanotrophs were present. Three Gleysols were incubated under different mixing ratios of (13)C-labelled methane to examine (13)C incorporation into phospholipid fatty acids (PLFAs). Phospholipid fatty acids typical of type II methanotrophs, 16:0 and 18:1omega7c, were labelled with (13)C in all soils after incubation under an atmosphere containing 30 ppmv of methane. Incubation under 500 ppmv of methane resulted in labelling of additional PLFAs besides 16:0 and 18:1omega7c, suggesting that the composition of the active methanotrophic community changed in response to increased methane supply. In two soils, 16:1 PLFAs typical of type I methanotrophs were strongly labelled after incubation under the high methane mixing ratio only. Type II methanotrophs are most likely responsible for atmospheric methane uptake in these soils, while type I methanotrophs become active when methane is produced in the soil.

Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2

“…Although the pMMO2 presumably allows type II methanotrophs to survive in dry upland soils for extended periods by consuming atmospheric methane, the overall activity response of strain SC2 during incubation at 1.75 ppmv CH 4 , including the slight decline in cell numbers, implies that these methanotrophic bacteria may not be sufficiently oligotrophic for permanent activity in this type of soil. Rather, the presence of two pMMO isozymes with different thresholds for methane oxidation suggests that these organisms play an important role in consuming atmospheric methane if their growth is periodically supported by methane produced in anoxic microsites, in anoxic deep soil layers, or during temporary flooding (11,(27)(28)(29). In support of this view, Methylocystis spp.…”

“…In support of this view, Methylocystis spp. were recently found to be the most abundant methanotrophs in various hydromorphic soils (11). These soils possess an oxic surface layer and subsurface zones that are usually anoxic and methanogenic because of permanent or periodic water saturation.…”

“…In contrast to methanotrophs in the aerobic interfaces of methanogenic environments, the methanotrophs active in dry, well aerated upland soils, for example, forest soils, consume methane with high apparent affinity (K m(app) values of 0.01-0.28 M CH 4 ) (6). Molecular studies have indicated the presence of type II methanotrophs in most upland soils (10,11) and have provided increasing evidence that, in these soils, the most abundant methanotrophs belong to several uncultivated groups, including upland soil cluster ␣ (USC␣) and upland soil cluster ␥ (USC␥) (10,12,13). Members of USC␣ and USC␥ are presumed to be specialized oligotrophs adapted to living solely on atmospheric methane.…”

Influence of elevated ozone concentration on methanotrophic bacterial communities in soil under field condition

“…The primers used were A189 (Bodrossy et al, 1997) and mb661 (Knief et al, 2006). Their sequences are listed in Table 1.…”

“…The specific primers of the 16S rRNA gene in methanotrophic bacteria were selected to distinguish between type I and type II methanotrophic bacteria. The primers A189 (Bodrossy et al, 1997)/mb661 (Knief et al, 2006) were used to quantify the pmoA gene copy number in the total methanotrophic bacteria. The primers MB10g/533r and MB9a/533r were used to quantify the 16S rRNA gene copy number of type I and type II methanotrophic bacteria (Henckel et al, 1999;Bodelier et al, 2000).…”