New Insight into the Role of the Calvin Cycle: Reutilization of CO2 Emitted through Sugar Degradation

Abstract

Ralstonia eutropha is a facultative chemolithoautotrophic bacterium that uses the Calvin–Benson–Bassham (CBB) cycle for CO2 fixation. This study showed that R. eutropha strain H16G incorporated 13CO2, emitted by the oxidative decarboxylation of [1-13C1]-glucose, into key metabolites of the CBB cycle and finally into poly(3-hydroxybutyrate) [P(3HB)] with up to 5.6% 13C abundance. The carbon yield of P(3HB) produced from glucose by the strain H16G was 1.2 times higher than that by the CBB cycle-inactivated mutants, in agreement with the possible fixation of CO2 estimated from the balance of energy and reducing equivalents through sugar degradation integrated with the CBB cycle. The results proved that the ‘gratuitously’ functional CBB cycle in R. eutropha under aerobic heterotrophic conditions participated in the reutilization of CO2 emitted during sugar degradation, leading to an advantage expressed as increased carbon yield of the storage compound. This is a new insight into the role of the CBB cycle, and may be applicable for more efficient utilization of biomass resources.

RubisCO selection using the vigorously aerobic and metabolically versatile bacterium Ralstonia eutropha

“…The presence of an efficient lithoautotrophic metabolism has attracted recent interest in tapping R. eutropha for biotechnological CO 2 utilization [3, 4, 39, 40]. The complementable R. eutropha strain H16ΔLS described here can now be exploited for RubisCO-selection studies, especially under robust aerobic growth conditions.…”

“…There has been considerable interest in using directed evolution strategies to improve the expression levels, assembly and kinetic performance of RubisCO so that the rates for net carboxylation may be maximized [5,[7][8][9][10][11][12][14][15][16][17][36][37][38]. The presence of an efficient lithoautotrophic metabolism has attracted recent interest in tapping R. eutropha for biotechnological CO 2 utilization [3,4,39,40]. The complementable R. eutropha strain H16DLS described here can now be exploited for RubisCO selection studies, especially under robust aerobic growth conditions.…”

“…It is uniquely suited to alternate between or concomitantly use heterotrophic (with sugars, organic acids, fatty acids or plant oils) or autotrophic (using CO 2 or formate) growth modes to drive cellular metabolism and the production of polyhydroxyalkanoates (PHAs). Industrial scalability of growth conditions and genetic amenability make R. eutropha an attractive host for use in the bioplastic and biofuel industries [3,4]. …”

Increased Dynamics of Tricarboxylic Acid Cycle and Glutamate Synthesis in Obese Adipose Tissue

“…In the metabolic turnover analysis, LC conditions were similar to those of the metabolome analysis. The MS conditions were described previously (20). In the static metabolic analysis, the final result for each sample was normalized to the respective protein content.…”

Studies on the aerobic utilization of synthesis gas (syngas) by wild type and recombinant strains of Ralstonia eutropha H16

“…The b-proteobacterium Ralstonia eutropha H16, currently named as Cupriavidus necator H16, represents a model organism for autotrophic lifestyle and has been studied extensively for its efficient utilization of carbon dioxide and hydrogen as carbon and energy sources (Friedrich and Schwartz, 1993). By means of enzymes of the Calvin-Benson-Bassham (CBB) cycle, R. eutropha H16 fixes CO 2 from the atmosphere as the sole source of carbon as well as from CO 2 , generated from its own intracellular oxidation of organic carbon compounds like formate (K€ arst and Friedrich, 1984;Shimizu et al, 2015). When growing lithotrophically, R. eutropha H16 oxidizes molecular hydrogen by a soluble and a membrane-bound hydrogenase, which are tolerant to oxygen, as well as to carbon monoxide Burgdorf et al, 2005;B€ urstel et al, 2016).…”