Novel multiphase loop reactor with improved aeration enables foam-free rhamnolipid production by Pseudomonas putida

The novel multiphase loop reactor is a modified airlift reactor with an internal loop enabling continuous in situ liquid-liquid extraction. In this study, the reactor is applied for a microbial production of biosurfactants. The obligate aerobic bacterium Pseudomonas putida KT2440 was engineered for rhamnolipid production. Rhamnolipids are biosurfactants with strong foaming capabilities making cultivations in an aerated stirred tank fermenter challenging. The continuous removal of rhamnolipids via in situ liquid-liquid extraction can remedy this foam challenge, and thereby supports long-term cultivation and production. The initially designed multiphase loop reactor had an oxygen transfer rate, which was too low to meet the oxygen demand of the whole-cell biocatalyst, resulting in inefficient growth and production. A re-design of the sparger via 3D-printing enabled a raise in oxygen supply allowed rhamnolipid production at key performance indicators that matched stirred-tank reactor cultivations, but with the advantage of enabling continuous cultivation in the future. Concluding, we present the successful use of the multiphase loop reactor for rhamnolipid synthesis, highlighting its potential to become a new platform technology for intensified bioprocessing.