Gene disruption to improve 1,3-propanediol production in Citrobacter braakii strain TB-96

Abstract

Crude glycerol is an excellent carbon source for bacterial production systems. Bacterial fermentation often generates by-products that can offer an additional carbon pool to improve the product profile for optimal valorization. In this study, the properties of two phylogenetically distinct bacteria, Acinetobacter baylyi ADP1 and Clostridium butyricum, were coupled in a one-pot batch process to co-produce 1,3 propanediol (PDO) and long-chain alkyl esters (wax esters, WEs) from crude glycerol. In the process, A. baylyi deoxidized the growth medium allowing glycerol fermentation and PDO production by C. butyricum. Reaeration of the co-cultivations enabled A. baylyi to metabolize the fermentation by-products, acetate and butyrate, and synthesize intracellular WEs. To improve PDO production and A. baylyi growth, carbon and macronutrients in the growth medium were screened and optimized using Plackett-Burman and Box-Behnken models. The validation experiment revealed a good correlation between the observed and predicted values. The salting-out method recovered 89.5% PDO from the fermentation broth and in vacuo extraction resulted in a PDO content of 5.3 g L−1. Nuclear magnetic resonance revealed a WE content and yield of 34.4 ± 1.4 mg L−1 and 34.2 ± 3.2 mg WE g−1 dry cell weight, respectively. A molar yield of 0.65 mol PDO mol−1 and 0.62 μmol WE mol−1 crude glycerol was achieved with the synthetic consortium. This work emphasizes the strength of response surface methodology in improving production processes from the mutualistic association of divergent bacterial species in consortium. The co-production of PDO and WEs from crude glycerol is demonstrated for the first time in this study.