An improved screening method for microorganisms able to convert crude glycerol to 1,3-propanediol and to tolerate high product concentrations

A new screening method was developed and established to find high-performance bacteria for the conversion of crude glycerol to 1,3-propanediol. Three soil samples from palm oil-rich habitats were investigated using crude glycerol of a German biodiesel plant. Nine promising 1,3-propanediol producers could be found. Because of a special pH buffer system, a fast evaluation on microscale and high 1,3-propanediol concentrations up to 40 g L⁻¹ could be achieved. Three strains demonstrated very high product tolerance and were identified as Clostridium butyricum. Two strains, AKR91b and AKR102a, grew and produced 1,3-propanediol in the presence of 60 g L⁻¹ initial 1,3-propanediol, the strain AKR92a even in the presence of 77 g L⁻¹ 1,3-propanediol. The strains AKR91b and AKR102a tolerated up to 150 g L⁻¹ crude glycerol and produced 80% of the 1,3-propanediol attained from pure glycerol of the same concentration. Further criteria for the choice of a production strain were the pathogenicity (risk class), ability to grow on low-cost media, e.g., with less yeast extract, and robustness, e.g., process stability after several bioconversions. Overall, the strain C. butyricum AKR102a was chosen for further process optimization and scale-up due to its high productivity and high final concentration in a pH-regulated bioreactor.