Lake Pavin History, geology, biogeochemistry, and sedimentology of a deep meromictic maar lake

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16.4 Biological Methane Consumption

Biological CH 4 oxidation is carried out by methanotrophs
which are estimated to consume 60 % of the biogenic CH 4
produced in the environment. In freshwater lakes, methano-
trophs oxidizes 30 to 99 % of the CH 4 produced (Bastviken
et al. 2008 ), and plays a fundamental role in regulation of
CH 4 emissions. Two biological pathways may be involved in
CH 4 oxidation^12 :

• The aerobic methane oxidation which was first described
  at the beginning of the twentieth century (Kaserer 1905 ;
  Sohngen 1906 ). The activity of aerobic CH 4 -oxidizing
  bacteria depends on the availability and concentrations of
  both CH 4 and O 2. The highest CH 4 consumption rates are
  located at oxic/anoxic interfaces where opposite fluxes of
  CH 4 and O 2 occur (Fig. 16.5).


• The anaerobic methane oxidation pathway which, until
  the 1970s, was thought to be unrealistic. The microorgan-

isms involved in this process have only been identified

during the last decade, but have not been isolated in pure

culture so far. They are anaerobic microorganisms, such

as methanogens, and their activities are located in the

anoxic compartments (Fig. 16.5).

16.4.1 Aerobic Methanotrophy

16.4.1.1 Aerobic Methanotrophs

All known aerobic methanotrophs belong to the domain

Bacteria and constitute a polyphyletic group belonging to 4

families affiliated to the γ-Proteobacteria (Methylococcaceae,

Methylocystaceae), the α-Proteobacteria (Beijerinckiaceae)

and to the Verrucomicrobia (Methylacidiphilaceae).

• Methylococcaceae (known as Type I methanotrophs): the
  intracytoplasmic membrane (ICM) forms bundles of
  vesicular disks distributed throughout the cell. These
  methanotrophs use the ribulose monophosphate pathway

Fig. 16.5 Methanotrophs in Lake Pavin. (a) Schematic representa-
tion of CH 4 and O 2 profiles along the water column of Lake Pavin.
(b) Composition of methanotrophic communities, determined from
pmoA gene clones libraries. Depths for which pmoA transcripts of
Methylobacter were detected are indicated by a star (adapted from
Biderre-Petit et al. 2011 ). (c) Transmission electron micrograph and
phylogenetic affiliation (based on 16S rRNA) of methanotrophic
strains MT2 and MT3 (Mcystis = Methylocystis) isolated from the
water column of Lake Pavin. (d) Thermograms representing the heat

production by the strain MT2 (unpublished results), measured using

microcalorimetry (Box 16.2). (e) Schematic representation of impor-

tance of the anaerobic oxidation of methane processes in the water

column of Lake Pavin (adapted from Lopes et al. 2011 ). (f)

Thermograms representing the heat production of water samples

collected at 70 m depth in the water column of Lake Pavin (unpub-

lished results), measured using microcalorimetry (Box 16.2).

Incubations were performed under N 2 and CH 4 (1 atm and 3 atm

pressure)

(^12) For more details, several reviews can be found on aerobic (Hanson
and Hanson 1996 ; Trotsenko and Murrell 2008 ) and anaerobic
oxidation of methane (Knittel and Boetius 2009 ; Thauer and Shima
2008.
16 Methanogens and Methanotrophs in Lake Pavin
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