Efficient Production of Poly-3-hydroxybutyrate by <i>Photobacterium</i> sp. TLY01 Using Hydrolysate of Cassava Powder as the Carbon Source

Poly-3-hydroxybutyrate (PHB) is an industrially significant biopolymer with abundant potential applications to replace traditional plastics. Carbon substrates contribute to a large portion of the PHB production cost. In this study, cost-effective cassava powder was employed as the substrate to synthesize PHB by Photobacterium sp. TLY01. The combination of ultrasound and deep eutectic solvent (DES) pretreatment was found to significantly improve the efficiency of enzymatic hydrolysis of cassava powder. Under optimized conditions, the highest saccharification yield of fermentable monosaccharides reached 96.92%. In addition, the DES solution could be recycled up to 10 times, and eventually, the glycerol component in the DES could be utilized as a carbon source for bacterial fermentation. Scanning electron microscope observations indicated that the structure of cassava powder changed from a compact and regular structure to a dispersed and broken state. The hydrolysate of cassava powder was employed to cultivate Photobacterium sp. TLY01 in bioreactors, in which 64.71 g/L of poly-3-hydroxybutyrate (PHB) was obtained during fed-batch fermentation. These results provide a promising way for converting low-value, nongrain products into value-added biodegradable polymers.