Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) is a biodegradable biopolymer produced by numerous microorganisms, and the bacterium Cupriavidus necator is one of the most studied. Considering its high production cost, cultivation strategies aimed at increasing process productivity have been studied. The aim of this work was to produce P(3HB-co-3HV) from C. necator in a system with external cell recycling and feeding limited concentrations of nitrogen during the production phase. Two cultures with cell recycling were performed: one conducted in depletion of nitrogen and another one where this nutrient was supplied in limited concentrations, during the production phase. The concentration of the carbon source (glucose) used to feed the bioreactor aimed to simulate an agro-industrial waste with low carbon concentration (90 g.L-1). Propionic acid was fed to the bioreactor continuously after the start of the production phase in order to stimulate the production of HV units. For the cultures conducted in depletion of the nitrogen source the values of Xr (residual biomass) and P(3HB-co-3HV) were equal to 16.6 and 44.6 g.L-1, which represents 72.9 % of biopolymer content and, equal to 22.5 and 54.9 g.L-1, which represents 70.9 % of biopolymer, for the culture with feeding of the nitrogen source. The percentage of biopolymer was lower in cultivation fed in nitrogen, however, the production of Xr and P(3HB-co-3HV) at the end of the culture was higher than for the culture with depletion of nitrogen, which promoted an increase in process productivity. The productivities for the cultures conducted in depletion and feeding of nitrogen source, during the production phase, were 0.87 and 1.06 g.L-1.h-1, respectively. It can be concluded that the system with external cell recycle, conducted with nitrogen feed, is a good alternative to the use of agro-industrial waste (molasse and vinasse, for example) with low carbon concentration to increase productivity in the production of P(3HB-co-3HV).