Lecture 35: Carbon Cycle 2: Decomposers, Methanogenic Archaea and MethylotrophsMMG 301 Fall 2002 Page 1 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 CH4MMG 301 Fall 2002 Page 2 Habitats of fermentative communities anoxic sediments (esp. freshwater), sewage sludge digesters, landfills, animal intestinal tracts.MMG 301 Fall 2002 Page 3 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 → CO2MMG 301 Fall 2002 Page 4 Genus prefix “Methylo” Figs 19.44b↓ (Methylomonas methanica) and 19.45 (Methylocystis parvus)
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