Ronald D. Jones1, Richard Y. Morita1
1Department of Microbiology and School of Oceanography, Oregon State University, Corvallis, Oregon 97331.
Tóm tắt
Chemolithotrophic ammonium-oxidizing and nitrite-oxidizing bacteria including
Nitrosomonas europaea, Nitrosococcus oceanus, Nitrobacter
sp.,
Nitiospina gracilis
, and
Nitrococcus mobilis
were examined as to their ability to oxidize methane in the absence of ammonium or nitrite. All ammonium oxidizers tested had the ability to oxidize significant amounts of methane to CO
2
and incorporate various amounts into cellular components. None of the nitrite-oxidizing bacteria were capable of methane oxidation. The methane-oxidizing capabilities of
Nitrosococcus oceanus
and
Nitrosomonas europaea
were examined with respect to ammonium and methane concentrations, nitrogen source, and pH. The addition of ammonium stimulated both CO
2
production and cellular incorporation of methane-carbon by both organisms. Less than 0.1 mM CH
4
in solution inhibited the oxidation of ammonium by
Nitrosococcus oceanus
by 87%. Methane concentrations up to 1.0 mM had no inhibitory effects on ammonium oxidation by
Nitrosomonas europaea.
In the absence of NH
4
-N,
Nitrosococcus oceanus
achieved a maximum methane oxidation rate of 2.20 × 10
−2
μmol of CH
4
h
−1
mg (dry weight) of cells
−1
, which remained constant as the methane concentration was increased. In the presence of NH
4
-N (10 ppm [10 μg/ml]), its maximum rate was 26.4 × 10
−2
μmol of CH
4
h
−1
mg (dry weight) of cells
−1
at a methane concentration of 1.19 × 10
−2
mM. Increasing the methane concentration above this level decreased CO
2
production, whereas cellular incorporation of methane-carbon continued to increase.
Nitrosomonas europaea
showed a linear response throughout the test range, with an activity of 196.0 × 10
−2
μmol of CH
4
h
−1
mg (dry weight) of cells
−1
at a methane concentration of 1.38 × 10
−1
mM. Both nitrite and nitrate stimulated the oxidation of methane. The pH range was similar to that for ammonium oxidation, but the points of maximum activity were at lower values for the oxidation of methane.
