title: From CO2 to cell: energetic expense of creating biomass using the Calvin-Benson-Bassham and reductive citric acid cycles based on genome data.
abstract: The factors driving the dominance of the Calvin-Benson-Bassham cycle (CBB) or reductive citric acid cycle (rCAC) in autotrophic microorganisms in different habitats are debated. Based on costs for synthesizing a few metabolic intermediates, it has been suggested that the CBB poses a disadvantage due to higher metabolic cost. The purpose of this study was to extend this estimate of cost from metabolite synthesis to biomass synthesis. For 12 gammaproteobacteria (CBB) and five epsilonproteobacteria (rCAC), the amount of ATP to synthesize a gram of biomass from CO2 was calculated from genome sequences via metabolic maps. The eleven central carbon metabolites needed to synthesize biomass were all less expensive to synthesize via the rCAC (66%-89% of the ATP needed to synthesize them via CBB). Differences in cell compositions did result in differing demands for metabolites among the organisms, but the differences in cost to synthesize biomass were small among organisms that used a particular pathway (e.g. rCAC), compared to the difference between pathways (rCAC versus CBB). The rCAC autotrophs averaged 0.195 moles ATP per g biomass, while their CBB counterparts averaged 0.238. This is the first in silico estimate of the relative expense of both pathways to generate biomass.
authors.affiliation: Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Mangiapia
authors.affiliation: Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA kmscott@usf.edu.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Scott
mesh_terms: D052818:Autotrophic Processes / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D018533:Biomass; D057486:Carbon Cycle / Q000235:genetics; D002245:Carbon Dioxide / Q000378:metabolism*; D002952:Citric Acid Cycle / Q000235:genetics*; D003198:Computer Simulation; D004269:DNA, Bacterial / Q000235:genetics; D004734:Energy Metabolism; D020565:Epsilonproteobacteria / Q000235:genetics / Q000378:metabolism*; D020563:Gammaproteobacteria / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D060086:Hydrothermal Vents / Q000382:microbiology; D009876:Operon; D010788:Photosynthesis
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D002245:Carbon Dioxide
keywords: Calvin cycle; autotroph; carbon fixation; deep-sea; hydrothermal; reductive citric acid cycle