Study shows the CellMaker outperforms traditional stirred tank reactor in production of carotenoids

The CellMaker Airlift bioreactor outcompetes a traditional stirred tank reactor in production of carotenoids, valuable secondary metabolites from yeast, a study has shown.

The Cellexus CellMaker systems are designed to be flexible, and to be used with most bioprocesses. The CellMaker bioreactor has a long-proven track record in fermentation of bacteriophages or recombinant proteins and we are expanding into the recombinant antibody production, cell and gene therapy and stem cell research areas to expand our offer even further. However, not all biotechnological products are created by the means of genetic modification. Many naturally produced secondary metabolites can be valuable compounds, as is the case with carotenoids. These naturally occurring pigments are produced by many species of plants, algae, fungi and bacteria. Many have also found use as antioxidants, or antibacterial and antitumor agents. A way to efficiently produce these compounds is a highly desirable development in industrial biotechnology, however, a transfer of technology from traditional stainless-steel fermenters and optimising industry-standard single use bioreactors for this process can be challenging.

In 2019, a group of Romanian researchers published a paper in the journal Revista de Chimie (Mihalcea, A., Onu, A., Chirvase, A. A. & Ungureanu, C.; Rev. Chim. (2019) 70, 124–127) where they tested the feasibility of using SU systems for carotenoid production from yeast Rhodotorula rubra. The authors have tested 3 types of bioreactors: a traditional reusable continuously stirred tank reactor (CSTR), a rocking wave-motion single use bioreactor and the Cellexus CellMaker Regular single-use airlift system. All three tested systems operate using very different principles, creating a very interesting study setup to compare various cultivation conditions. Additionally, 3 variants of growth media were used in 3 sets of experiments, comparing the effects of nutrients available from carotenoids production. The principal idea of this study was to establish if the carotenoid mix containing Torularhodin can be produced as efficiently in a single use bioreactor, compared to the traditional CSTR regularly used in their laboratory.

From the 3 technologies tested in the study, the CSTR yielded the highest biomass in all 3 conditions tested, with the CellMaker matching the biomass yield in 2 out of 3 conditions. The essential experimental difference in the conditions, where the CellMaker was outcompeted by the CSTR, was the source of organic nitrogen. The authors have found that NH4H2PO4 is much more bioavailable than NH4NO3, and the additional phosphates further stimulates the growth of R. rubra, which explained the initial growth difference. The third medium used (NH4)2SO4 as nitrogen source yielding similar biomass in all 3 bioreactors.

Upon the analysis of the produced carotenoids, the authors have found more significant differences, which were not directly linked to the biomass yield. The yeast grown in the CellMaker have generated the highest quantities of the target carotenoid, Torularhodin, in both conditions with NH4NO3 and NH4H2PO4, despite the fact the biomass yield in the first experimental setup was significantly lower than in the CSTR. The yield of carotenoids per unit volume in the CellMaker was 44% higher than in the CSTR in the first medium and 20% higher under the optimal growth conditions, in comparison to the CSTR. The rocking bed bioreactor did not produce competitive quantities of carotenoids in any of the tested conditions and, despite good biomass yield, the production of carotenoids in the media supplemented with (NH4)2SO4 was very low in all fermenters.

The results of this study have shown that the SU technologies can successfully replace traditional steel tank reactors in production of valuable secondary metabolites. The finding that the CellMaker has not only provided the best production yields, but also the best yield per gram of biomass, shows that optimisation of any bioprocess is an essential step to success. Providing optimal growth environment for the cells in the bioprocess, here in the airlift single use CellMaker bag, are just as important as achieving the best possible production yields, as optimising the media. We were delighted to see the results of this study and we wish the authors many more successes in their work.