Synthesis of poly-3-hydroxybutyrate (PHB) by Bacillus cereus using grape residues as sole carbon source

Abstract

ABSTRACT Polyhydroxyalkanoates (PHA) are bacterial polyesters that have been described as one of the most promising sustainable alternatives to petroleum-based plastics. A major challenge for PHA to become market-competitive, is to decrease the associated production costs. According to several studies, about 20–50% of the total production costs is attributed to the raw materials and therefore, the use of different types of organic residues have been evaluated as substrates for the microorganisms. In this study, the strain Bacillus cereus ATCC 14579 was cultivated in shake flasks using a defined medium and pretreated grape peel as sole carbon source. The pretreatment of the grape peels was performed by a hydrolysis step with diluted sulfuric acid yielding up to 52.9% (w/w) of total sugars from the dry residue. PHB extraction using dry and wet biomass was performed and evaluated showing up to 3.7-higher yields when using the latter. PHB accumulation of 18.79% (w/w), corresponding to 0.53 gPHB/L, was achieved using the grape peel hydrolyzate at 72 h of cultivation. Eventually, the possibility of producing PHB by the use of non-treated lignocellulosic biomass (LCB) with high contents of fermentable sugars is presented as an interesting alternative to be optimized and projected for sustainable bioplastic production processes.