8. REACTIONS OF INORGANIC SUBSTANCES
401
thiocyanate oxidation are clearly adaptive, while those involved in thiosulfate degradation are constitutive.
De Kruyff and co-workers (217) found that the ability to oxidize
thiocyanate is not restricted to T. thiocyanooxidans. Under aerobic conditions thiocyanate is utilized as a substrate in place of thiosulfate by
typical strains of T. thioparus and T. denitrificans, but not by T. thiooxidans. Moreover, the three species which can carry out this aerobic
reaction can also grow anaerobically in the presence of thiocyanate and
nitrate. Under these conditions, nitrate is reduced to N 2 by T. denitrificans but only to nitrite by the other two species. These recent observations suggest that there are no significant differences between T. thiocyanooxidans and T. denitriftcans.
C. OXIDATION OF METHANE
The oxidation of methane may be included into the group of biological litho-oxidations due to the fact that, from the biochemical point
of view, CH 4 may be thought of not only as an organic compound—
the first member of the series of paraffin hydrocarbons—but also as the
product of the complete reduction of C0 2 . This interpretation agrees
with the demonstration by Barker and associates (21) of the biological
formation of methane by the direct reduction of carbon dioxide rather
than by the degradation of organic compounds of several carbon atoms.
It also agrees with the fact that methane is used as the sole source of
energy and carbon by microorganisms whose behavior resembles closely
that of other chemo-lithotrophic bacteria.
The methane-oxidizing bacteria were discovered by Söhngen (218)
in 1906. The species he described under the name of Bacillus methanicus
is now known as Methanomonas methanica and has been studied in
detail by Hutton and ZoBell (219) and Hutton (220). It is a short
bacillus or coccobacillus, very mobile, Gram-negative, with a single
polar flagellum. M. methanica is a strict aerobe and grows actively in an
atmosphere containing methane and oxygen, forming a characteristic
pellicle at the surface of liquid media.
The over-all oxidation of methane is summarized in this reaction:
CH 4 + 20 2 = C0 2 + 2H 2 0
(-AF° 298 ° = +207 kcal.)
It certainly comprises several successive steps but these have not yet
been elucidated.
Slavnina (221) found that M. methanica can oxidize ethane and
propane as well as methane. Hutton (220) characterized another species,
M. carbonatophila, which differs primarily by the absence of a pellicle in
liquid cultures.
401
thiocyanate oxidation are clearly adaptive, while those involved in thiosulfate degradation are constitutive.
De Kruyff and co-workers (217) found that the ability to oxidize
thiocyanate is not restricted to T. thiocyanooxidans. Under aerobic conditions thiocyanate is utilized as a substrate in place of thiosulfate by
typical strains of T. thioparus and T. denitrificans, but not by T. thiooxidans. Moreover, the three species which can carry out this aerobic
reaction can also grow anaerobically in the presence of thiocyanate and
nitrate. Under these conditions, nitrate is reduced to N 2 by T. denitrificans but only to nitrite by the other two species. These recent observations suggest that there are no significant differences between T. thiocyanooxidans and T. denitriftcans.
C. OXIDATION OF METHANE
The oxidation of methane may be included into the group of biological litho-oxidations due to the fact that, from the biochemical point
of view, CH 4 may be thought of not only as an organic compound—
the first member of the series of paraffin hydrocarbons—but also as the
product of the complete reduction of C0 2 . This interpretation agrees
with the demonstration by Barker and associates (21) of the biological
formation of methane by the direct reduction of carbon dioxide rather
than by the degradation of organic compounds of several carbon atoms.
It also agrees with the fact that methane is used as the sole source of
energy and carbon by microorganisms whose behavior resembles closely
that of other chemo-lithotrophic bacteria.
The methane-oxidizing bacteria were discovered by Söhngen (218)
in 1906. The species he described under the name of Bacillus methanicus
is now known as Methanomonas methanica and has been studied in
detail by Hutton and ZoBell (219) and Hutton (220). It is a short
bacillus or coccobacillus, very mobile, Gram-negative, with a single
polar flagellum. M. methanica is a strict aerobe and grows actively in an
atmosphere containing methane and oxygen, forming a characteristic
pellicle at the surface of liquid media.
The over-all oxidation of methane is summarized in this reaction:
CH 4 + 20 2 = C0 2 + 2H 2 0
(-AF° 298 ° = +207 kcal.)
It certainly comprises several successive steps but these have not yet
been elucidated.
Slavnina (221) found that M. methanica can oxidize ethane and
propane as well as methane. Hutton (220) characterized another species,
M. carbonatophila, which differs primarily by the absence of a pellicle in
liquid cultures.