Poly-3-(R)-hydroxybutyrate (PHB) is a biobased polymer with different biological roles and biotechnological applications. In this project, we studied its accumulation in the bacteria Escherichia coli and Rhodospirillum rubrum under anaerobic conditions, combining different approaches.

Some bacterial species generate poly-3-(R)-hydroxybutyrate (PHB) coupled to NADPH reoxidation while other species generate this polymer using NADH. Given the different physiological roles of NAD(H) and NADP(H), it is expected that PHB accumulation has different functions depending on the kind of cofactor used during its accumulation. In this context, the observation and engineering of the genes and proteins enabling PHB accumulation in Rhodospirillum rubrum (a natural PHB producer) and Escherichia coli (a bacterium where it is possible to introduce the PHB production pathway) should improve (i) our understanding of the PHB accumulation as a biological process and (ii) our interventions to promote PHB accumulation for biotechnological purposes. Broadly speaking, Rhodospirillum rubrum has a versatile metabolism, including the possibility of using CO as an energy source. During the anaerobic growth of this bacterium, it is possible to observe different carbon partitions between PHB and biomass while supplying CO combined with other electron and/or carbon source(s). However, our understanding of the biological processes and operative conditions that determine the partition of the carbon between PHB and the rest of the biomass is limited. A better comprehension of these biological processes and operative conditions should contribute to our basic knowledge of the metabolic laws ruling the fate of the electrons and the carbon during the anaerobic growth and to applied biotechnological approaches for the production of tailored polyhydroxyalkanoates at a lower cost. On the other hand, the possibility to easily introduce PHB production pathways in E. coli is a convenient tool for the above mentioned purposes.