Unveiling the potential of a novel alkalophilic Citrobacter freundii IIPDR3 strain in valorizing glycerol to 1,3-propanediol

Abstract

Glycerol-based biotechnological production of 1,3-propanediol (PDO) has taken center stage after its recent commercialization by Metabolic Explorer. The present study unveils the potential of a novel alkalophilic, BSL-1 bacterium Citrobacter freundii IIPDR3 to produce 1,3-PDO from glycerol. The culture conditions were optimized at shake flask level using one-variable-at-a-time (OVAT) approach, and statistically significant parameters were identified. The optimal conditions for batch production of 1,3-PDO were phosphate-buffered glycerol-based medium essentially containing 1.5 gL−1 ammonium sulfate, 3 gL−1 yeast extract, and 0.5 gL−1 magnesium sulphate, temperature 36 °C, pH–stat of 8.0, and inoculum size being ≥ 35 µgbacterial cells/mL on dry cell weight (DCW) basis. Incorporation of 0.2% Tween 80 in the fermentation medium improved glycerol uptake rate and prevented self-flocculation of bacterial cells. Using liquor NH3 as a neutralizing agent, C. freundii IIPDR3 produced a maximum of 18.04 ± 0.76 gL−1 1,3-PDO from pure glycerol, with productivity and yield being 1.72 gL−1 h−1 and 0.53 gg−1, respectively. When the robustness of the strain was tested on crude glycerol (CG), it accumulated 9.65 and 11.11gL−1 1,3-PDO in 7 h and 10.5 h with initial glycerol concentrations of 20 and 40 gL−1, respectively. The study confirms that C. freundii IIPDR3 can be a promising candidate to tackle CG, a prominent waste derived from biodiesel industry, and simultaneously upgrade it to valorized products such as 1,3-PDO.