Biofabrication of polyhydroxybutyrate (PHB) in engineered Cupriavidus necator H16 from waste molasses

Background

Cupriavidus necator H16, a native polyhydroxybutyrate (PHB) producer, has emerged as a promising candidate for sustainable bioproduction to replace conventional plastics. However, most fermentation processes still rely on expensive substrates. Therefore, developing an eco-friendly bioprocess for PHB using waste materials is urgent and essential.

Method

An engineered strain Lgg-H16, incorporating galactose permease (galP) and glucokinase (glk), was employed to boost glucose uptake and phosphorylation. Then, biomass and PHB production were improved by fine-tuning the carbon, nitrogen, and phosphorus ratios. Yeast extract was supplemented as an additional nutrient, and a tailored feeding strategy was applied to maximize PHB output. To lower the manufacturing costs, waste molasses from the sugar industry, was utilized for fed-batch fermentation. The physical properties of the PHB, such as molecular weight and crystallinity, were analyzed using differential scanning calorimeter (DSC) and gel permeation chromatography (GPC), respectively.

Significant results

Engineered Lgg-H16 strain exhibited a 2.15-fold increase in specific growth rate compared to the wild type with a C:N:P ratio of 20:1:18, as well as supplemented 2 g/L yeast extract in the medium. PHB yield reached 17.4 g/L with 70 % content from waste molasses in fed-batch fermentation with an atomizer to increase gas dispersion, costing only 1 % of pharmaceutical-grade glucose. All physical properties of the PHB produced by Lgg-H16 were comparable to commercial product, supporting this promising bioprocess by using the low-cost feedstocks for high-value bioplastic PHB.