Abstract

Poly(3-hydroxybutyrate) (P(3HB)) is a biopolymer produced by many microorganisms, in unbalanced media conditions. One of the most studied biopolymer producer microorganisms is the bacterium Cupriavidus necator. Many studies have been done to understand the metabolic pathways of this bacterium and, based on this knowledge, the metabolic flux analysis (MFA) for the assimilation of different substrates, in the P(3HB) production, was developed. It is possible to apply the MFA to build structured models able to describe and predict the behavior of this microorganism in specifics scenarios. The purpose of the present study was to develop a structured model capable of predicting the behavior of C. necator, in the P(3HB) production, through the assimilation of glucose. Two scenarios of P(3HB) production, under nitrogen and oxygen limitation, were evaluated after the development of the model. To build the model, 17 intermediate metabolites and 15 reactions were considered in the metabolic network, based in the MFA studies presented in the literature. For each reaction, an equation with the Monod (for multiples substrates) structure was written considering the reactions activation or inhibition by intermediate metabolics. The mass balance of the system was considered and the system of ordinary differential equations was solved using the software Matlab. This model may describe the behavior of the intra and extracellular metabolites, as glucose, ATP, Acetyl-CoA, P(3HB), between others, during the culture, that can be used to define which scenario may promote the best results related to growth or P(3HB) production, depending on the goal of the study. For the first scenario evaluated, in the present study, it was possible to notice that when the nitrogen limitation happened, the biomass production stopped, and the accumulation of P(3HB), that was small before the limitation, increased substantially, once the flux of the Acetyl-CoA was redirected to the P(3HB) production instead of the biomass. In the second scenario, with oxygen limitation, the P(3HB) production increased, however, differently than at the nitrogen limitation, the biomass production did not stop, because the oxygen needed to be supplied in limited amounts to maintain the viability of the cells. Since, in this case, the Acetyl-CoA was used to produce biomass and P(3HB), the specific P(3HB) production rate was lower than in the first scenario. The structured model developed in this work could represent the behavior of C. necator reported in the literature and can be applied as a predictive model.