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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)

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Bacterial physiology micr430

Bacterial Physiology (Micr430)

Lecture 7

C1 Metabolism

(Text Chapter: 13)



  • 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)

Bacterial physiology micr430

Calvin Cycle: key reactions

Bacterial physiology micr430

Calvin Cycle

Bacterial physiology micr430

RuBP carboxylation

Fig 13.1

Bacterial physiology micr430

Calvin cycle, glycolysis and PPP

Fig 13.3

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

Bacterial physiology micr430


Pathway in Clostridium

Fig 13.4

Bacterial physiology micr430


Pathway in Methanogens

Fig 13.7



  • 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

Bacterial physiology micr430

Reductive TCA cycle

Fig 13.9



  • 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

Bacterial physiology micr430

Serine Pathway

Fig 13.11

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