Sustainable Production of Poly(3-hydroxybutyrate) Using Eucalyptus Bark: Integration with Green Downstream Processing

This study integrates the valorization of a lignocellulose material into poly-(3-hydroxybutyrate), P-(3HB), with biopolymer extraction from bacterial cells with the enzyme alcalase. The work focused on Burkholderia thailandensis DSM 13276 as the P-(3HB) producer and on eucalyptus bark, a byproduct from the pulp industry, as the sole feedstock for bacterial cultivation. The eucalyptus bark was hydrolyzed by a cellulolytic enzymatic cocktail following steam explosion and further subjected to ultrafiltration for enzyme recovery. The resulting hydrolysate supported good cell growth, achieving a cell dry weight of 7.67 ± 0.16 g/L within 72 h of cultivation, and high P-(3HB) content (60.0 ± 2.19 wt %) in the bacterial cells, clearly favoring biopolymer synthesis over cell growth, as demonstrated by the polymer and growth yields (0.190 g_P(3HB)/g_sugar and 0.026 g_X/g_sugar, respectively). High extraction efficiency (96%) and biopolymer purity (100 ± 3.38%) were reached by enzymatic treatment, resulting in a sample with properties aligned with those of commercial P-(3HB) in terms of molecular mass distribution, crystallinity, and thermal properties. These findings demonstrate the successful use of a sustainable feedstock together with the application of environmentally friendly technologies based on the use of enzymes for both lignocellulosic saccharification and biopolymer recovery to develop high-quality bioplastics, advancing the goals of a circular bioeconomy.