ESPM 131 Lecture Notes - Lecture 20: Syntrophy, Methylamine, Euryarchaeota
14 May 2018
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Lecture 20: Methane in Soil
●Methane : most reduced naturally-occurring form org C
○Maybe most abundant org compound on Earth
○Flammable GHG that absorbs IR, long-lived in lower atmosphere (9 yr)
○Lower conc than CO2, but 25x more potent, 3x incr since pre-ind, 1%/yr
○Sources :
■Wetlands, rice ag
■Ruminants, termites
■Oceans: anaerobic decomp at bottom
○Sinks : tropospheric oxidation, stratospheric loss, soils (largest biotic sink)
○Production: methanogens
■CH4 as waste prod
■Archaea - diverse phylog and morphol
■Strict anaerobes
■obligate/facultative autotrophs
■Most use H2/CO2, formate, acetate, methanol, methylamine (simple C)
■Euryarchaeota
■Hydrogenotrophic : 4H2 + CO2 → CH4 + 2H20
■acetotrophic/acetoclastic: CH3COOH → CH4 + CO2
■Methyl coenzyme M reductase (MCR) : catalyzes last step of both rxns, we have
primers for MCRa gene
■Conditions:
●Anaerobic: some have genes for O2 detox, some from deserts
●Redox potential is low: pe = -4, most exogenous acceptors have been
used (NO3-, FeIII ← why not in tropical soils, SO4 ← available - why it’s
not in oceans)
○Controls: soil moisture, bio O2 demand (BOD) , subst avail of alt
e- acceptors, temp, heterogeneity
○Where: looded soils, wet w/ high microbe activity and limited
gas dif
●Dependent on simple substrates and other microbes (hetero fermenters,
anaerobic respirers)
●Syntrophy : relationship in which 2 bacteria are dependent on each other
for nutrition
○May be with S physical groups for methanogens
○Low H2 conc for facult anaerob oxidizing bacteria to make
acetate
○H2 transferred from secondary fermentation to methanogens
○Alt oxidants use up acetate/monomers
○Hydrogenotrophic orgs compete for it
○Requires physical closeness
○Consumption: methanotrophs
■CH4 as a substrate
Document Summary
Methane : most (cid:418)edu(cid:283)ed natu(cid:418)all(cid:482)-o(cid:283)(cid:283)u(cid:418)(cid:418)in(cid:322) (cid:321)o(cid:418)m o(cid:418)(cid:322) c. Ma(cid:482)(cid:282)e most a(cid:282)undant o(cid:418)(cid:322) (cid:283)ompound on ea(cid:418)th. Flamma(cid:282)le ghg that a(cid:282)so(cid:418)(cid:282)s ir, lon(cid:322)-li(cid:475)ed in lo(cid:476)e(cid:418) atmosphe(cid:418)e (cid:1827)9 (cid:482)(cid:418)(cid:1828) Lo(cid:476)e(cid:418) (cid:283)on(cid:283) than co(cid:1681), (cid:282)ut (cid:1681)(cid:1684)(cid:481) mo(cid:418)e potent, (cid:1682)(cid:481) in(cid:283)(cid:418) sin(cid:283)e p(cid:418)e-ind, (cid:1680)%/(cid:482)(cid:418) Sinks : t(cid:418)oposphe(cid:418)i(cid:283) o(cid:481)idation, st(cid:418)atosphe(cid:418)i(cid:283) loss, soils (cid:1827)la(cid:418)(cid:322)est (cid:282)ioti(cid:283) sink(cid:1828) Most use h(cid:1681)/co(cid:1681), (cid:321)o(cid:418)mate, a(cid:283)etate, methanol, meth(cid:482)lamine (cid:1827)simple c(cid:1828) H(cid:482)dro(cid:322)enotrophi(cid:283) : (cid:1683)h(cid:1681) + co(cid:1681) ch(cid:1683) + (cid:1681)h(cid:1681)(cid:1679) Meth(cid:482)l (cid:283)oenz(cid:482)me m redu(cid:283)tase (cid:1827)mcr(cid:1828) : (cid:283)atal(cid:482)zes last step o(cid:321) (cid:282)oth (cid:418)(cid:481)ns, (cid:476)e ha(cid:475)e p(cid:418)ime(cid:418)s (cid:321)o(cid:418) mcra (cid:322)ene. Anae(cid:418)o(cid:282)i(cid:283): some ha(cid:475)e (cid:322)enes (cid:321)o(cid:418) o(cid:1681) deto(cid:481), some (cid:321)(cid:418)om dese(cid:418)ts. Redo(cid:481) potential is lo(cid:476): pe = -(cid:1683), most e(cid:481)o(cid:322)enous a(cid:283)(cid:283)epto(cid:418)s ha(cid:475)e (cid:282)een used (cid:1827)no(cid:1682)-, feiii (cid:476)h(cid:482) not in t(cid:418)opi(cid:283)al soils, so(cid:1683) a(cid:475)aila(cid:282)le - (cid:476)h(cid:482) it"s not in o(cid:283)eans(cid:1828) Cont(cid:418)ols: soil moistu(cid:418)e, (cid:282)io o(cid:1681) demand (cid:1827)bod(cid:1828) , su(cid:282)st a(cid:475)ail o(cid:321) alt e- a(cid:283)(cid:283)epto(cid:418)s, temp, hete(cid:418)o(cid:322)eneit(cid:482) Whe(cid:418)e: (cid:500)looded soils, (cid:476)et (cid:476)/ hi(cid:322)h mi(cid:283)(cid:418)o(cid:282)e a(cid:283)ti(cid:475)it(cid:482) and limited (cid:322)as di(cid:498)(cid:321)
