MMG 301
Fall 2002
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Lecture 35: Carbon Cycle 2: Decomposers, Methanogenic Archaea and Methylotrophs
(unless noted otherwise, all figures & tables are from: Microbial Life by Perry, Staley & Lory (2002)  Sinauer Associates, Inc.)
Comparison of respiratory versus fermentative decomposition of “biomass”
Respiratory (can often be accomplished by single species of microbes)
aerobic
anaerobic
CH4 (-4) ↔ CH3OH (-2) ↔ HCHO (0) ↔ HCOOH (+2) ↔ CO2 (+4)
“biomass”
Fermentative (requires many different species, cooperating in an anaerobic food web)
Desired end products: CO2 + CH4 (why are these desireable??)
e.g.
nC6H12O6 (cellulose, a major component
of plant biomass)
↓
3n CO2 + 3n CH4
MMG 301
Fall 2002
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Habitats of fermentative communities
anoxic sediments (esp. freshwater), sewage sludge digesters, landfills, animal intestinal tracts.
MMG 301
Fall 2002
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Methanogenic Archaea: “Methano” prefix: Methanobrevibacter, Methanosarcina, etc.
Strict anaerobes; terminal organisms in anaerobic food webs; thermodynamically help “pull” anaerobic
decomposition processes (forming CH4 ± CO2 as products).
-
Presumptive ID in natural samples by UV autofluorescence of F420 (an e carrier).
Methylotrophs: Bacteria that aerobically oxidize one-carbon compounds, including methane (CH4; by
a special subset, “methanotrophs”) or multi-C compounds lacking C-C bonds, e.g. H3C-O-CH3
(dimethylether).
MMO
CH4 → CH3OH → HCHO → HCOOH → CO2
MMG 301
Fall 2002
Genus prefix “Methylo”
Figs 19.44b↓ (Methylomonas methanica)
and 19.45 (Methylocystis parvus) →
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