Environmental Microbiology of Aquatic and Waste Systems

11.4 Anaerobic Breakdown of Organic Matter in Landfills (and Aquatic Sediments) 299

kandleri. Examples of the coccoid methanogens

include species from Methanococcus and Methano­

sphaera to name a few. Metha noculleus and

Methanogenium are coccoid as well but are irregu-

larly shaped, possibly due to S-layers not being so

strongly bonded like other wall structures.

Methanogens are not just limited to these shapes,

but include a plate shaped genus Methanoplanus,

Methanospirillum that are long thin spirals, and

Methanosarcina that are cluster of round cells.

(b) Lack of mureins in their cell walls

Methanogens lack murein typical of bacteria

(eubacteria), but some contain pseudomurein,

which can only be distinguished from its bacteria

counterpart through chemical analysis. Those

methanogens that do not possess pseudomurein

have at least one paracrystalline array (S-layer).

An S-layer is made up of proteins that fit together

in an array like jigsaw pieces that do not covalently

bind to one another, in contrast to a cell wall that

is one giant covalent bond. Also, some methano-

gens have S-layer proteins that are glycosylated,

which could increase stability, while others do not

(e.g., Methanococcus spp).

(c) Ecological distribution in Extreme environments

Methanogens are found in extreme environments:

from the hot vents in the ocean floor to the polar

ice to hot springs.

11.4.2 Landfill Gas

Landfill gas is the gas released from landfills. The gas

produced by landfills contains about 50% each of

methane (CH 4 ) and carbon dioxide (CO 2 ). Methane is a

Organic Materials

in Aquatic Sediments

and in Landfills

CO 2

CH 4

Anaerobic Respiration

Fermentation

Aerobic Respiration

H 2

O 2

H 2 O

H 2 O

CO 2

1/2

CO 2

NO3- N 2

Anaerobic Respiration

CO 2

CO 2

H 2 S

CO 2

SO 22 −

CH 3 COOH CH 3 CH 2 OH

+

CH 3 COOH

CH 4 +

+H 2 +

Fig. 11.10 Breakdown
of organic matter in the
anaerobic regimes of
landfill and aquatic
sediments

Table 11.5 Some substrates utilized by methanogens (Modified
from Rehm and Reed 2008 )

CO 2 + H 2 Carbon dioxide + hydrogen gas
HCOO– Formate
CO + H 2 Carbon monoxide + Hydrogen gas
CH 3 OH Methanol
CH 3 NH3+ Methylamine
(CH 3 )2NH2+ Dimethylamine
(CH 3 )3NH+ Trimethylamine
CH 3 SH Mehtylmercaptan
(CH 3 )2S Dimethylsulphide
CH 3 COO– Acetate