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Bacterial Physiology (Micr430). Lecture 7 C1 Metabolism (Text Chapter: 13). Definition. C 1 compounds are organic compounds lacking C-C bonds Methylotrophs – organisms which use C 1 compounds other than CO 2 as sole sources of energy and carbon

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bacterial physiology micr430

Bacterial Physiology (Micr430)

Lecture 7

C1 Metabolism

(Text Chapter: 13)

definition
Definition
  • C1 compounds are organic compounds lacking C-C bonds
  • Methylotrophs – organisms which use C1 compounds other than CO2 as sole sources of energy and carbon
  • Methanotrophs - organisms which use methane as sole sources of energy and carbon
  • Methanogens – organisms that can produce methane
carbon dioxide fixation
Carbon Dioxide Fixation
  • There are three major autotrophic CO2 fixation pathways in prokaryotes:
    • Calvin cycle (or Calvin-Benson-Bassham)
    • Reductive TCA cycle
    • The Acetyl-CoA Pathway
calvin cycle 2 stages
Calvin Cycle – 2 stages
  • Stage 1, reductive carboxylation of ribulose-1,5-bisphosphate (RuBP) to form phosphoglyceraldehyde (PGALD), catalyzed by RubisCO
  • Stage 2, sugar rearrangements to regenerate three RuBPs from five of six PGALDs
calvin cycle
Calvin Cycle
  • Only two reactions are unique to this cycle (the others are the same as the oxidative pentose phosphate pathway):
    • Phosphoribulokinase
    • Ribulose bisphosphate carboxylase (RubisCO)
  • This cycle constitutes the dark reaction of photosynthesis
  • Six turns of the cycle result in the synthesis of 1 mol of hexose (F-6-P)
the acetyl coa pathway
The Acetyl-CoA Pathway
  • Bacteria that use this pathway include methanogens, acetogenic bacteria and most autotrophic sulfate-reducing bacteria
  • Acetyl-CoA is made from CO2 via Acetyl-CoA pathway
  • Acetyl-CoA then is incorporate into cell material as carbon source
slide11

Acetyl-CoA

Pathway in Clostridium

Fig 13.4

slide12

Acetyl-CoA

Pathway in Methanogens

Fig 13.7

methanogensis
Methanogensis
  • Methanogensis from CO2 and H2
  • Methanogensis from acetate
reductive tca cycle
Reductive TCA cycle
  • Reductive TCA pathway is used by
    • Desulfobacter (strict anaerobic)
    • Chlorobium (strict anaerobic)
    • Hydrogenobacter (aerobic)
    • Archaea
  • Overall reaction is the synthesis of one mole of oxaloacetate from four moles of CO2.
reductive tca cycle1
Reductive TCA cycle
  • Three new enzymes are needed to reverse TCA cycle:
    • Fumarate reductase (step 4)
    • a-Ketoglutarate synthase (step 6)
    • ATP-dependent citrate lyase (step 11)
  • In addition, pyruvate synthase replaces pyruvate dehydrogenase, and PEP synthetase replaces pyruvate kinase
methylotrophs
Methylotrophs
  • Compounds used for methylotrophic growth include:
    • Methane
    • Methanol
    • Formaldehyde
    • Formate
    • Methylamine
    • Trimethylamine (multicarbon but without C-C)
c1 carbon assimilation
C1 carbon assimilation
  • Methylotrophs assimilate C1 carbon source via either ribulose-monophosphate pathway or the serine pathway
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