Flux Balance Analysis of Rhodobacter sphaeroides anaerobic metabolism
Faculty of Physics, Chair of Biophysics, Moscow State University, Leninskiye Gory 1/2, Moscow 119991, Russia1 pp. (accepted)
Purple non-sulfur bacterium Rhodobacter sphaeroides is one of the most versatile organisms with respect to metabolism. In aerobic conditions this bacterium grows chemoheterotrophically by respiration, while in anaerobic conditions it switches to photoheterotrophic or photoautotrophic mode in the presence of light or to fermentation. Besides it is considered as a potential source of polyhydroxybutyrate and molecular hydrogen industrial production. R. sphaeroides vital functions were investigated in a great number of works, and it is a target of many knockout studies. However there is no accurate mathematical model of metabolism of this bacterium yet.
Here we present a variant of such model construction based on Flux Balance Analysis (FBA). FBA enables to predict metabolic fluxes at cellular level from known stoichiometry of reactions in steady state approximation. By means of this method in the last decade several stoichiometric models of bacterial cells were constructed. The central moment of such metabolism modeling is the selection of so called objective function which simulates the “goal” of cell activity. While it is a common practice to choose for this role biomass formation, we propose another objective function, light absorption rate, which is by our opinion more appropriate for phototrophic metabolism.
We have constructed stoichiometric model of R. sphaeroides primary photoheterotrophic metabolism, which includes all central metabolic pathways of a bacterial cell (glycolysis, pentose phosphate pathway, TCA cycle), as well as amino acids, lipids, chlorophyll, caratenoids, polyhydroxybutyrate and hydrogen biosynthesis pathways. Here the first results of modeling are presented. It is shown that there is a good agreement between resultant fluxes from modeling of bacterial growth on acetate and their known experimental values, so the model can be considered as adequate. This model will help to extend our knowledge of purple bacteria activity in anaerobic conditions as well as to investigate possible ways to affect its metabolism.