cycle, (4) 3-Hydroxypropionate cycle, (5) Hydroxypropionate–hydroxybutyrate
cycle, (6) Dicarboxylate–hydroxybutyrate cycle (Atomi 2002; Madigan et al.
2003). These are the pathways which sequester carbon dioxide.
11.4.1 Calvin Cycle
It is the major and most abundant pathway for CO 2 fixation. This cycle works in
some aerobic or facultative anaerobic Proteobacteria, green sulfur bacteria, genera
Sulfobacillus, algae, cyanobacteria, and plants. In this cycle, carbon dioxide reacts
with the ribulose 1,5-bisphosphate in the presence of Rubisco enzyme to yield two
molecule of 3-phosphoglycerate, from which the sugar is regenerated (Calvin and
Massini 1952). In this pathway, several enzymes are involved but the key enzymes
and CO 2 fixing enzyme is Rubisco.
11.4.2 Reverse Krebs Cycle
This cycle occurs in green sulfur bacterium Chlorobium limicola. The complex
carbon molecules of Krebs cycle is acetyl CoA which oxidized to form CO 2 and
water. In the reverse Krebs cycle takes CO 2 and water to make complex organic
compounds acetyl CoA (Evans et al. 1966). Although several enzymes are involved
in this pathways but 2-Oxoglutarate synthase, 2-Oxoglutarate synthase and ATPcitrate lyaseare are some key enzymes. The CO 2 fixing enzymes are isocitrate
dehydrogenase, pyruvate synthase and carboxylazing PEP (Fig. 11.2) (Buchanan
and Arnon 1990; Berg et al. 2010).
11.4.3 Reductive Acetyl Coenzyme A Pathway
In this pathway one molecule of CO 2 is reduced to CO and another one is reduced to
a methyl group (bound to carrier); consequently. Acetyl-CoA is synthesized from
CO and the methyl group. This is the most energetically autotrophic carbon fixation
pathway (Ragsdale 2008). This cycle occurs strictly in anaerobic species which
includes proteobacteria, planktomycetes, spirochaetes and euryarchaeota. In this
pathway the key enzymes and CO 2 fixing enzymes are Acetyl-CoA synthase and
CO dehydrogenase (Berg et al. 2010).
11.4.4 Hydroxypropionate Cycle
This cycle is found in only some green non-sulfur bacteria Chloroflexus aurantiacus
(family Chloroflexaceae) (Fig. 11.3). The pathway has not been found elsewhere. In
this cycle Acetyl-CoA reacts with HCO 3
À in the presence of ATP to form malonylCoA which is reduced to 3-Hydroxypropionate. Then converted to four carbon
compound succinyl-CoA, which is oxidized to malyl-CoA. Finally, the cleavage
11 Sequestration of Carbon Dioxide by Microorganism and Production of Value. . .
239
cycle, (6) Dicarboxylate–hydroxybutyrate cycle (Atomi 2002; Madigan et al.
2003). These are the pathways which sequester carbon dioxide.
11.4.1 Calvin Cycle
It is the major and most abundant pathway for CO 2 fixation. This cycle works in
some aerobic or facultative anaerobic Proteobacteria, green sulfur bacteria, genera
Sulfobacillus, algae, cyanobacteria, and plants. In this cycle, carbon dioxide reacts
with the ribulose 1,5-bisphosphate in the presence of Rubisco enzyme to yield two
molecule of 3-phosphoglycerate, from which the sugar is regenerated (Calvin and
Massini 1952). In this pathway, several enzymes are involved but the key enzymes
and CO 2 fixing enzyme is Rubisco.
11.4.2 Reverse Krebs Cycle
This cycle occurs in green sulfur bacterium Chlorobium limicola. The complex
carbon molecules of Krebs cycle is acetyl CoA which oxidized to form CO 2 and
water. In the reverse Krebs cycle takes CO 2 and water to make complex organic
compounds acetyl CoA (Evans et al. 1966). Although several enzymes are involved
in this pathways but 2-Oxoglutarate synthase, 2-Oxoglutarate synthase and ATPcitrate lyaseare are some key enzymes. The CO 2 fixing enzymes are isocitrate
dehydrogenase, pyruvate synthase and carboxylazing PEP (Fig. 11.2) (Buchanan
and Arnon 1990; Berg et al. 2010).
11.4.3 Reductive Acetyl Coenzyme A Pathway
In this pathway one molecule of CO 2 is reduced to CO and another one is reduced to
a methyl group (bound to carrier); consequently. Acetyl-CoA is synthesized from
CO and the methyl group. This is the most energetically autotrophic carbon fixation
pathway (Ragsdale 2008). This cycle occurs strictly in anaerobic species which
includes proteobacteria, planktomycetes, spirochaetes and euryarchaeota. In this
pathway the key enzymes and CO 2 fixing enzymes are Acetyl-CoA synthase and
CO dehydrogenase (Berg et al. 2010).
11.4.4 Hydroxypropionate Cycle
This cycle is found in only some green non-sulfur bacteria Chloroflexus aurantiacus
(family Chloroflexaceae) (Fig. 11.3). The pathway has not been found elsewhere. In
this cycle Acetyl-CoA reacts with HCO 3
À in the presence of ATP to form malonylCoA which is reduced to 3-Hydroxypropionate. Then converted to four carbon
compound succinyl-CoA, which is oxidized to malyl-CoA. Finally, the cleavage
11 Sequestration of Carbon Dioxide by Microorganism and Production of Value. . .
239