Changes in a glycerol-degrading bacterial community in an upflow anaerobic reactor for 1,3-propanediol production

The evolution of the bacterial community in an up-flow anaerobic reactor with silicone support, continuously fed with pure glycerol (day 0-293) and crude glycerol (day 294-362), was studied. Biomass from a former glycerol-degrading reactor was used as inoculum. The maximum yield and productivity of 1,3-propanediol (PDO) (0.62 mol.mol-gly^-1 and 14.7 g.L^-1.d^-1, respectively) were obtained with crude glycerol. The inoculum had low diversity, with dominance of Lactobacillus (70.6%) and Klebsiella/Raoultella (23.3%). After 293 days of feeding with pure glycerol, the abundance of both taxa decreased to less than 10%, either in the attached biofilm or in the biomass growing in suspension. The genus Clostridium and members of the Ruminococcaceae family then became the majority. In the period after feeding with crude glycerol, Clostridium remained as the majority genus in the biofilm; however, it was partially replaced in the suspension by Eubacterium, a non-glycerol degrading bacterium. This fact, together with the prevalence of other glycerol-degrading genera in the biofilm, such as Caproiciproducens and Lactobacillus, indicated that the bacteria attached to the silicone support were responsible for converting glycerol into 1,3-PDO. Therefore, to increase the 1,3-PDO productivity, a good approach would be to maximize the amount of reactor support. Other genera that do not degrade glycerol, such as Anaerobacter and Acetomaculum, thrived at the expense of cellular decay material. The Canonical Correspondence Analysis demonstrated that the origin of glycerol is an important variable to consider during the bioreactor operation for producing 1,3-PDO, while the glycerol loading rate is not. KEY POINTS: • Microbial community showed robustness in a range of operational conditions. • A significantly high 1,3-propanediol yield can be achieved using crude glycerol. • The attached biofilm appears to be key to the high production of 1,3-propanediol.