Extended biosynthesis of rhamnolipid by immobilized Pseudomonas aeruginosa USM-AR2 cells in a fluidized bed bioreactor

Abstract

Abstract This study aims to evaluate rhamnolipid production by immobilized Pseudomonas aeruginosa USM-AR2 cells using waste cooking oil (WCO) as the carbon source. P. aeruginosa USM-AR2 cells were entrapped in polyvinyl alcohol (PVA)-alginate hydrogel beads. The performance of entrapped cells was compared with free cells in shake flasks before cultivation in a custom-designed fluidized bed reactor (FBR). A mass of 1 g of wet cells entrapped in PVA-alginate hydrogel beads was successfully recycled three times in shake flasks at 200 rpm, producing between 0.66 to 1.34 g L−1 rhamnolipid after 120 h. Meanwhile, cultivation of entrapped cells in FBR with broth recirculation showed that the suitable hydrogel beads to medium ratio was 1:20 at an aeration rate of 0.5 vvm, producing between 0.77 to 1.58 g L−1 rhamnolipid and degrading 8.67 to 20.93g L−1 of waste cooking oil in 15 cycles of repeated batch cultivation. Entrapped P. aeruginosa USM-AR2 cells achieved a higher rhamnolipid production by 1.03-fold during cycle 3 in shake flasks and 1.19-fold during cycle 11 in an FBR, compared to free cells. These results show that entrapment enables the reusability of viable cells and maintains the stability of rhamnolipid production throughout the extended cultivation, increasing cell tolerance to perturbations in fermentation conditions.