Towards economic and sustainable production of poly-3-hydroxybutyrate by Halomonas boliviensis using as feedstock industrial residues of seaweed Gelidium corneum.

The production of the biopolymer poly-3-hydroxybutyrate (P3HB) by the halophile Halomonas boliviensis in fed-batch cultivations using bench-scale bioreactors was re-examined aiming to improve productivity and decrease production costs. To improve productivity, controlled feeding of glucose and nitrogen source, and supplementation of extra monosodium glutamate (MSG), phosphate, and trace elements were assessed. Non-aseptic conditions were investigated as a strategy to reduce costs related to medium and equipment sterilization. Further, to reduce production costs, glucose-rich hydrolysates derived from industrial residues of the red macroalga Gelidium corneum were used as an alternative carbon source to glucose. These hydrolysates were produced through hydrothermal pretreatment to remove residual agar followed by enzymatic hydrolysis. Enzyme recycling was evaluated as a strategy to improve process economics. After hydrolysis, the enzymatic cocktail was recovered using an ultrafiltration membrane and reused in the next batch. Supplementation of trace elements and increased phosphate addition contributed to a significant increase of cell dry weight (CDW), P3HB titer and overall P3HB volumetric productivity up to 103.1 ± 1.9 g/L, 70.9 ± 0.3 g/L, and 0.92 ± 0.04 g/L·h, respectively. Under non-aseptic conditions, P3HB titers and productivities were comparable to those achieved under axenic conditions. Algal hydrolysates proved to be an effective glucose source, yielding results similar to those obtained with commercial glucose. This study shows that H. boliviensis is a promising platform for P3HB production and can efficiently convert carbohydrate-rich residual biomass under non-sterile conditions.