TABLE 1.

Some characteristics of AAOB (nitrifying bacteria), methanotrophic bacteria, and unknown high-affinity methane oxidizers in soil^a

Bacteria	Phylogenetic affiliation	Membrane type	Major fatty acidsb	Key enzyme	Apparent Km for CH4 (μM)c	Vmax for CH4 (mmol · g of cells−1 · h−1)	Oxidation inhibited by C2H2, C2H4, DME, and COd	Growth inhibited by elevated NH3 concn	CH4 required to maintain activity	% Assimilation of oxidized CH4e
MAB
Group 1	γ-Proteobacteria	Stacked, central	14:0, 16:0, and 16:1 species	pMMO (+ some sMMO)	0.8–32	10–31	+	+	+	29–62
Group 2	α-Proteobacteria	Flat, peripheral	18:1 species	pMMO (+ some sMMO)	0.8–32	10–31	+	+	+	29–62
Soil high affinity	?	?	18:1 species	?	0.01–0.06	?	+	+	+	20–54
AAOB
Group 3	β-Proteobacteria	Flat, peripheral	16:0 and 16:1 species	AMO	2,000	0.03–0.59	+	−	−	0–17
Group 4	γ-Proteobacteria	Stacked, central	16:0 and 16:1 species	AMO	6.6	0.01–0.08	+	−	−	1–47

^aData from references 1, 2, 5, 9, 12, 17, 19, 20, 22, 28, 30, 31, 39, and 40. 

^bA major fatty acid is present at a concentration of >10% in at least one member of each group. 

^cThe values for nitrifiers were based on the K_i of CH₄ for ammonia oxidation. 

^dDME, dimethyl ether. 

^eThe fate of labelled methane in nitrifiers is not known. The apparent assimilation could be due to nonspecific labelling by formaldehyde or assimilation at the level of CO₂.