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. 2019 Sep 2;9(1):12638.
doi: 10.1038/s41598-019-49079-z.

Modeling the Interplay between Photosynthesis, CO2 Fixation, and the Quinone Pool in a Purple Non-Sulfur Bacterium

Adil Alsiyabi  1 , Cheryl M Immethun  1 , Rajib Saha  2
Affiliations

Modeling the Interplay between Photosynthesis, CO2 Fixation, and the Quinone Pool in a Purple Non-Sulfur Bacterium

Adil Alsiyabi et al. Sci Rep. .

Abstract

Rhodopseudomonas palustris CGA009 is a purple non-sulfur bacterium that can fix carbon dioxide (CO2) and nitrogen or break down organic compounds for its carbon and nitrogen requirements. Light, inorganic, and organic compounds can all be used for its source of energy. Excess electrons produced during its metabolic processes can be exploited to produce hydrogen gas or biodegradable polyesters. A genome-scale metabolic model of the bacterium was reconstructed to study the interactions between photosynthesis, CO2 fixation, and the redox state of the quinone pool. A comparison of model-predicted flux values with available Metabolic Flux Analysis (MFA) fluxes yielded predicted errors of 5-19% across four different growth substrates. The model predicted the presence of an unidentified sink responsible for the oxidation of excess quinols generated by the TCA cycle. Furthermore, light-dependent energy production was found to be highly dependent on the quinol oxidation rate. Finally, the extent of CO2 fixation was predicted to be dependent on the amount of ATP generated through the electron transport chain, with excess ATP going toward the energy-demanding Calvin-Benson-Bassham (CBB) pathway. Based on this analysis, it is hypothesized that the quinone redox state acts as a feed-forward controller of the CBB pathway, signaling the amount of ATP available.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Summary of the iRpa940 model statistics and validation. (A) Overall model statistics. (B) Model biomass component compositions. (C) Sources of gene annotation. (D) Gene essentiality analysis results. G: Growth (non-essential gene), NG: No Growth (essential gene).
Figure 2
Figure 2
Effect of the Quinol sink rate on: (A) Light uptake rate, (B) Growth rate, (C) Carbon source uptake rate, and (D) Carbon fixation rate for growth on four carbon sources. ace: acetate, but: butyrate, suc: succinate, fum: fumarate.
Figure 3
Figure 3
Comparison of model-predicted vs MFA-generated flux values for reactions involved in central carbon metabolism. (A) Metabolic flux map showing reaction rates for growth on acetate (B) Percentage error between model predictions and MFA flux values for growth on four carbon sources.
Figure 4
Figure 4
Effect of the light uptake rate on (A) Growth rate, (B) Carbon source uptake rate, (C) Carbon fixation rate, and (D) Carbon dioxide excretion rate for growth on four carbon sources. ace: acetate, but: butyrate, suc: succinate, fum: fumarate. In A, B, and D, the lines for succinate and fumarate lie on top of each other.
Figure 5
Figure 5
Schematic of a proposed mechanism for the interaction between the quinone redox state, electron transport rate, and carbon fixation. (A) High rate of quinol oxidation. (B) Low rate of quinol oxidation.
See this image and copyright information in PMC

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