High cell density propionic acid fermentation with an acid tolerant strain of Propionibacterium acidipropionici

Abstract

Propionic acid is an important chemical with wide applications and its production via fermentation is of great interest. However, economic production of bio-based propionic acid requires high product titer, yield, and productivity in the fermentation. A highly efficient and stable high cell density (HCD) fermentation process with cell recycle by centrifugation was developed for propionic acid production from glucose using an acid-tolerant strain of Propionibacterium acidipropionici, which had a higher specific growth rate, productivity, and acid tolerance compared to the wild type ATCC 4875. The sequential batch HCD fermentation at pH 6.5 produced propionic acid at a high titer of ∼40 g/L and productivity of 2.98 g/L h, with a yield of ∼0.44 g/g. The product yield increased to 0.53-0.62 g/g at a lower pH of 5.0-5.5, which, however, decreased the productivity to 1.28 g/L h. A higher final propionic acid titer of >55 g/L with a productivity of 2.23 g/L h was obtained in fed-batch HCD fermentation at pH 6.5. A 3-stage simulated fed-batch process in serum bottles produced 49.2 g/L propionic acid with a yield of 0.53 g/g and productivity of 0.66 g/L h. These productivities, yields and propionic acid titers were among the highest ever obtained in free-cell propionic acid fermentation.

Bio-produced Propionic Acid: A Review

“…It is noted that a significantly higher yield of 0.48 g*g -1 and productivity of ~3 g*L -1 *h -1 were obtained in the third batch, which achieved the highest cell density of ~49 g*L -1 in terms of the dry weight of the cell (corresponding to OD 244.8). The highest propionic acid titre of 42.7 g*L -1 obtained in the second batch also confirmed that ACT-1 had a relatively high tolerance to propionate at pH 6.5 [21].…”

“…Both the productivity and yield were comparable to those of high cell density sequential batch fermentations at pH 6.5, suggesting that ACT-1 can tolerate a propionic acid concentration in excess of 50 g*L -1 at pH 6.5 [21].…”

“…There are reported solutions that increase this tolerance. One of them is serial adaptation followed by screening and isolation of single colonies on propionate-containing agar plates [21]. Genetic engineering provides new tools for generating mutants with improved fermentation capabilities [3,22], e.g.…”

“…The second highest propionic acid productivity in Table 2 is 2.23 g*L -1 *h -1 achieved by fed-batch fermentation also with cell recycling [21]. Propionibacterium acidipropionici ACT-1 was used in the study, as well.…”

Microbial Propionic Acid Production

“…The benchmark for an economically feasible fermentation process by 2020 from sugar has been set at a yield of 0.6 g/g (1.52 mol propionate/mol glucose) and a productivity of 1 g/L/h [9]. Various fermentation technologies including batch, fed-batch, continuous fermentation and immobilised cells to prevent product inhibition [11][12][13][14][15] have been explored, but still fermentations fall short on simultaneously meeting both criteria (Table 2). While a single study simultaneously met both requirements, an exceptionally high initial biomass of~56g/L was used and a low final propionate titre of 34.5 g/L was achieved [15].…”