Construcció d’un model metabòlic genèric d’un microorganisme acetogènic del gènere clostridium

Abstract

Of all the existing mechanisms for the carbon dioxide fixation in the living beings, only the WoodLjungdahl (WLP) reductive pathway, used by acetogenic bacteria, sustains the two basic requirements for life: conservation of energy and the production of biomass. In this project, a prototype model is presented allowing the development of a methodology for the modeling of culture systems in a simulated bioreactor. To illustrate this methodology, a generic metabolic model of stationary state is developed in order to make predictions based on the environmental conditions. In addition, a biological study of the model bacteria (Clostridium ljungdahlii and Clostridium kluyveri) is performed to demonstrate that both bacteria have a Rnf complex responsible for the translocation of protons through the membrane that allows them to conserve energy.

The reductive pathway of CO2 leads to the formation of high energy density chemicals such as acetate, ethanol and butyrate. Metabolic reactions in this work take place at points very close to the thermodynamic equilibrium, which allows the acceptance of different assumptions. Therefore, the purpose of this work is based on the construction of a generic metabolic model of two model organisms (C. ljungdahlii and C. kluyveri) that describes the activation of different metabolic pathways depending on the environmental conditions of the cell. The results suggest that: (i) none of the reactions that take part in the carbon flow are directly responsible for the conservation of energy, which is why a complementary system –the Rnf complex– that connects the electronic transfer from reduced ferredoxin (Fd-2) to NAD +, is executed by carrying out a translocation of protons through the membrane (this same gradient of H+ is used by an ATPase to generate ATP); (ii) the only metabolic point that allows the conservation of energy is the Rnf complex; (iii) the total amount of energy obtained in the WL route in the form of ATP varies according to the involved enzymes proposed; (iv) C.ljungdahlii and C.kluyveri are considered as interesting organisms to be used as a microbial production platform; (v) there are certain parameters that directly affect the metabolic pathways and the results of the model.

Therefore, acetogenic bacteria are organisms of great study interest as they could be used as biocatalysts in the biotechnology industry, thanks to their capacity for fermentation of gases alike CO2