Sequential processing with fermentative Caldicellulosiruptor kronotskyensis and chemolithoautotrophic Cupriavidus necator for converting rice straw and CO₂ to polyhydroxybutyrate

Unpretreated rice straw was fermented by the extremely thermophilic bacterium Caldicellulosiruptor kronotskyensis, generating solubilized carbohydrates, organic acids, lignin-derived aromatics, H₂ , and CO₂ , which were subsequently used to produce polyhydroxybutyrate (PHB) by the chemolithoautotrophic bacterium Cupriavidus necator. The fermented liquid significantly enhanced the growth of C. necator, leading to a five-fold cell biomass yield, and a nine-fold PHB yield compared to what was obtained from conventional mineral media. This integrated process utilized all products of lignocellulose fermentation without H (electron) loss and carbon emission, while concomitantly enhancing CO₂ fixation by C. necator for PHB production. The sequential coupling of C. kronotskyensis and C. necator provides not only a new biorefinery paradigm characterized by reduced pretreatment and saccharification requirements but also an efficient way for enhancing CO₂ fixation.