Crude glycerol is an ideal feedstock for bioproduction of 1,3-propanediol (1,3-PDO) while pure culture always shows low substrate tolerance and limited productivity. In this study, an anaerobic microbial consortium for conversion of crude glycerol was selected and its 1,3-PDO production capacity was evaluated. The consortium was obtained from anaerobic activated sludge by 19 serial transfers and mainly consisted of 94.64% Clostridiaceae and 4.47% Peptostreptococcaceae. The consortium adapted well with high glycerol concentration of 120 g/L as well as wide substrate concentration fluctuation from 15 to 80 g/L, producing 60.61 and 82.66 g/L 1,3-PDO in the batch and fed-batch fermentation, with the productivity of 3.79 and 3.06 g/(L∙h), respectively, which are among the best results published so far. Furthermore, mini consortia isolated by serial dilution exhibited similar microbial composition but gradually decreasing tolerance to crude glycerol. Four randomly selected Clostridium butyricum displayed different substrate tolerance and insufficient 1,3-PDO production capacity. This work demonstrated that the high adaptation to crude glycerol of the consortium was the collaborative effort of different individuals.
One of the important targets of industrial biotechnology is using cheap biomass resources. The traditional strategy is microbial fermentations with single strain. However, cheap biomass normally contains so complex compositions and impurities that it is very difficult for single microorganism to utilize availably. In order to completely utilize the substrates and produce multiple products in one process, industrial microbiome based on microbial consortium draws more and more attention. In this review, we first briefly described some examples of existing industrial bioprocesses involving microbial consortia. Comparison of 1,3-propanediol production by mixed and pure cultures were then introduced, and interaction relationships between cells in microbial consortium were summarized. Finally, the outlook on how to design and apply microbial consortium in the future was also proposed.
1,3-Propanediol (1,3-PD) is a versatile bulk chemical and widely used as a monomer to synthesis polymers, such as polyesters, polyethers and polyurethanes. 1,3-PD can be produced by microbial fermentation with the advantages of the environmental protection and sustainable development. Low substrate tolerance and wide by-product profile limit microbial production of 1,3-PD by Klebsiella pneumonia on industrial scale. In this study, microbial consortia were investigated to overcome some disadvantages of pure fermentation by single strain. Microbial consortium named DL38 from marine sludge gave the best performance. Its bacterial community composition was analyzed by 16S rRNA gene amplicon high-throughput sequencing and showed that Enterobacteriaceae was the most abundant family. Compared with three K. pneumonia strains isolated from DL38, the microbial consortium could grow well at an initial glycerol concentration of 200 g/L to produce 81.40 g/L of 1,3-PD with a yield of 0.63 mol/mol. This initial glycerol concentration is twice the highest concentration by single isolated strain and more than the critical value (188 g/L) extrapolated from the fermentation kinetics for K. pneumonia. On the other hand, a small amount of by-products were produced in batch fermentation of microbial consortium DL38, especially no 2,3-butanediol detected. The mixed culture of strain W3, Y5 and Y1 improved the tolerance to glycerol and changed the metabolite profile of single strain W3. The batch fermentation with the natural proportion (W3: Y5: Y1 = 208: 82: 17) was superior to that with other proportions and single strain. This study showed that microbial consortium DL38 possessed excellent substrate tolerance, narrow by-product profile and attractive potential for industrial production of 1,3-PD.
Ionic liquids (ILs) as "green" solvents have been widely used owing to their excellent properties, e.g., for biodiesel production. Crude glycerol as a by-product in biodiesel production is an ideal feedstock for the microbial production of 1,3-propanediol (PDO), which is a versatile bulk chemical. PDO can be produced by microbial consortium with the advantages of high substrate tolerance and narrow by-product profile. In the present study, the effect of IL 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][TfO]) was evaluated on the capacity of PDO production from crude glycerol by microbial consortium DL38-BH. In the batch fermentation at 60 g/L crude glycerol and 10 g/L [Emim][TfO], the concentration and yield of PDO from glycerol increased from 23.14 g/L and 0.45 mol/mol to 31.17 g/L and 0.60 mol/mol, respectively. Our results showed that [Emim][TfO] decreased the ratio of intracellular NADH to NAD and increased the concentration of 3-HPA during batch fermentation. The activities of three key enzymes in glycerol metabolism were stimulated by [Emim][TfO] during the batch fermentation by microbial consortium DL38-BH. Compared to the control, the proportion of Klebsiella genus which could convert glycerol to PDO increased significantly from 79.19% to 89.49% and the other genera that did not produce PDO were dramatically decreased (P < 0.05) at the end of batch fermentation. This work demonstrated that [Emim][TfO] significantly improved the concentration and yield of PDO from crude glycerol by adjusting microbial community during batch fermentation by microbial consortium.
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