Technical-Economical Approach for PHB Production by Ralstonia Eutropha Strain Using Concentrated Vinasse as Carbon Source and Other Biotechnological Applications

Abstract

The Brazilian ethanol industry is one of the most important in the global market, however these important industrial activities have been generating significant amounts of vinasse and its management has become costly for distilleries. In this study, the aim was to evaluate concentrated and in natura vinasse as basal culture media for biotechnological processes. Different bacteria and processes were assessed: L-threonine production by E. coli THR14, with glucose as carbon source; PHB production by halophilic strain Halomonas sp. HG03, with sucrose as carbon source; and PHB biosynthesis by R. eutropha L359PCJ, which used glycerol from vinasse as carbon source. Strains were evaluated firstly in shake flasks cultivations using vinasse-based media. E. coli THR14 had no statistical difference for biomass and L-threonine concentrations among control and vinasse-based treatments (up to 50% v v-1 of in natura vinasse). Halomonas sp. HG03 and R. eutropha L359PCJ were cultivated in mineral media diluted by in natura (50% and 75% v v-1) and concentrated (50% and 75% v v-1) vinasses. Higher vinasse concentrations resulted in higher cellular growth rather than PHB accumulation for both bacteria. In vinasse-based treatments, Halomonas sp. HG03 had PHB content between 19.6 – 75.2% and R. eutropha L359PCJ, 48.4 – 68.5%. 50% (v v-1) of concentrated vinasse was the most attractive condition for PHB production by both bacteria. Further experiments in CSTR bioreactors used this nutritional condition and R. eutropha L359PCJ had PHB content of 66.3%, concentrations of residual cell dry weight (rCDW) = 9.4 g L-1 and PHB = 18.6 g L-1, with YX/S = 0.16 g gGLYCEROL-1, YP/S = 0.32 g gGLYCEROL-1 and 0.25 gPHB Lh-1. Halomonas sp. HG03 had PHB content of 45.7%, rCDW = 9.8 g L-1, PHB = 8.3 g L-1 and YX/S = 0.18 g gSUCROSE-1, YP/S = 0.16 g gSUCROSE-1 and 0.12 gPHB Lh-1. Finally, cost reductions of PHB production by R. eutropha L359PCJ with concentrated vinasse-based medium were evaluated in silico by using SuperPro Designer. As a partial source of glycerol and other nutrients for PHB production by R. eutropha L359PCJ, vinasse reduced overall production costs by 13%. Simulated processes that used concentrated vinasse-based media combined with improvements of PHB productivity and higher cellular densities had production costs between US$ 3.9 – 7.5/kgPHB and 2.6 – 7.3 years of payback time.