Response and adaptation of different methanotrophic bacteria to low methane mixing ratios

Abstract

Described genera of methanotrophic bacteria are present in most upland soils, but it is not known whether these are sufficiently oligotrophic to oxidize methane at its trace atmospheric mixing ratio of 1.75 ppmv. Members of the genera Methylocystis, Methylosinus, Methylocaldum and Methylobacter were isolated from different upland soils and compared with type strains for growth and activity under low methane mixing ratios. The specific affinity (a0s) varied by about one order of magnitude among different methanotrophs. It was highest in some Methylocystis spp., suggesting that these were the most oligotrophic. In direct tests, the threshold mixing ratio of methane required by most methanotrophs for growth ranged from 100 to greater than 1000 ppmv. However, two Methylocystis strains grew at only 10-100 ppmv of methane and one oxidized atmospheric methane for >3 months with little or no decline in the absolute rate. The results show that some cultivated methanotrophic bacteria are much more oligotrophic than others, and may contribute to atmospheric methane oxidation in soils. However, it is likely that these need additional energy sources for long-term survival, and that uncultivated groups of methanotrophic bacteria are primarily responsible for the process in soils possessing high methane oxidation rates.

The Impact of Aridification and Vegetation Type on Changes in the Community Structure of Methane-Cycling Microorganisms in Japanese Wetland Soils

“…Physiological characterizations of isolated methanotrophs (types I and II) have shown that the growth of type I methanotrophs is greater than that of type II methanotrophs at higher methane concentrations, whereas type II methanotrophs outgrow type I under relatively low methane concentrations. [45][46][47] Taken together with previous observations, our findings strongly suggest that the rate of methane emission, linked to vegetation type, is a decisive factor determining the predominance of particular methanotrophs in a wetland.…”

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

“…The a s 0 values of pMMO2 determined for wild-type strain SC2 and mutant SC2-P2 (Table 4) were higher than those measured for cultured methanotrophs recently tested for their response to low methane mixing ratios (7). Of the strains studied in ref.…”

“…7. In brief, the serum vials were connected to a 54-liter gas reservoir (2 ϫ 27-liter plastigas bags, Linde) via tygon and iso-versinic tubes.…”

One millimetre makes the difference: high-resolution analysis of methane-oxidizing bacteria and their specific activity at the oxic–anoxic interface in a flooded paddy soil

“…This is much higher than the atmospheric methane concentration (1.8 ppm v , corresponding to 2.3 nM), but cultures of and sequences affiliated to Methylosarcina have so far only been retrieved from high-methane environments, such as lake sediments, rice paddies and landfills (Wise et al, 2001;Kalyuzhnaya et al, 2005;Henneberger et al, 2011;. Apparent K m constants in environments with high source strength are usually 41 mM CH 4 (Conrad, 1996), but some cultivated MOB, in particular Methylocystis strains, may grow for an extended period at 120 nM CH 4 and less (Knief and Dunfield, 2005). For Methylosarcina-like MOB, however, activity at low methane concentrations has not yet been reported.…”