Consumption of sugars and inhibitors of softwood hemicellulose hydrolysates as carbon sources for polyhydroxybutyrate (PHB) production with Paraburkholderia sacchari IPT 101

Abstract

The future industrial success of the compostable bio-polyesters known as polyhydroxyalkanoates, which includes polyhydroxybutyrate (PHB), depends mainly on their production using cheaper carbon sources than food-derived glucose. The existing pulp and paper infrastructure enables an alternative sugar supply in the form of wood hydrolysates. Softwood hemicellulose hydrolysates have a favourable sugar profile for fermentations and can be produced in such emerging integrated forest biorefineries. The processes can lead to varying amounts of inhibitors which can lead to the reduction or prevention of bacterial growth. A dilute acid pretreatment was used to produce a softwood hemicellulose hydrolysate containing the sugars mannose, xylose, glucose, galactose, and arabinose. To study the effects of increasing sugar diversity and inhibitor concentration, the softwood hydrolysate was mixed in varying proportions with a hardwood holocellulose hydrolysate obtained from the TMP-Bio process (a thermomechanical pulping-based process producing glucose and xylose). In fermentations with Paraburkholderia sacchari IPT 101, the sugars were depleted at different rates in the following order: glucose, mannose, xylose, galactose, and arabinose. All potential inhibitors except phenols were metabolized. The maximum cell dry weight reached 6.7 ± 0.1 g/L with 71 ± 5% PHB with hardwood holocellulose hydrolysate after 48 h. The analyses of the sugar and inhibitor consumption provided valuable information to validate approaches for the detoxification of softwood hemicellulose hydrolysates. Overall, the detoxification would allow PHB production in an integrated softwood biorefinery scheme.