Optimizing the DO-stat protocol for enhanced production of thermostable pullulanase in Escherichia coli by using oxygen control strategies

Method for high-efficiency fed-batch cultures of recombinant Escherichia coli

Fed-batch processes are commonly used in industry to obtain sufficient biomass and associated recombinant protein or plasmids. In research laboratories, it is more common to use batch cultures, as the setup of fed-batch processes can be challenging. This method outlines a robust and reliable means to generate Escherichia coli biomass in a minimum amount of fermentation time using a standardized fed-batch process. Final cell densities can reach over 50g dry cell weight per liter (gdcw/L) depending on the strain. This method uses a predefined exponential feeding strategy and conservative induction protocol to achieve these targets without multiple trial and error studies. If desired, productivity can be optimized by balancing the induction time and feed rates. This method utilizes cost-efficient defined media, minimizes process control complexity, and potentially aids downstream purification.

Microbial starch debranching enzymes: Developments and applications

Starch debranching enzymes (SDBEs) hydrolyze the α-1,6 glycosidic bonds in polysaccharides such as starch, amylopectin, pullulan and glycogen. SDBEs are also important enzymes for the preparation of sugar syrup, resistant starch and cyclodextrin. As the synergistic catalysis of SDBEs and other starch-acting hydrolases can effectively improve the raw material utilization and production efficiency during starch processing steps such as saccharification and modification, they have attracted substantial research interest in the past decades. The substrate specificities of the two major members of SDBEs, pullulanases and isoamylases, are quite different. Pullulanases generally require at least two α-1,4 linked glucose units existing on both sugar chains linked by the α-1,6 bond, while isoamylases require at least three units of α-1,4 linked glucose. SDBEs mainly belong to glycoside hydrolase (GH) family 13 and 57. Except for GH57 type II pullulanse, GH13 pullulanases and isoamylases share plenty of similarities in sequence and structure of the core catalytic domains. However, the N-terminal domains, which might be one of the determinants contributing to the substrate binding of SDBEs, are distinct in different enzymes. In order to overcome the current defects of SDBEs in catalytic efficiency, thermostability and expression level, great efforts have been made to develop effective enzyme engineering and fermentation strategies. Herein, the diverse biochemical properties and distinct features in the sequence and structure of pullulanase and isoamylase from different sources are summarized. Up-to-date developments in the enzyme engineering, heterologous production and industrial applications of SDBEs is also reviewed. Finally, research perspective which could help understanding and broadening the applications of SDBEs are provided.

Effective production of single-chain variable fragment (scFv) antibody using recombinant Escherichia coli by DO-stat fed-batch culture

Dissolved oxygen (DO)-stat fed-batch culture, which allows a high cell density culture of microorganisms under constant DO conditions, was applied to anti-CRP single-chain variable fragment (scFv) production using recombinant Escherichia coli. The DO-stat fed-batch culture was successfully performed under various DO conditions for more than 50 h, resulting in increased scFv production from 0.5 to 0.8 g/L by flask and batch cultures to 2.8-3.0 g/L by the fed-batch culture under the conditions of 5-40% of DO saturation. The formation of inclusion bodies was effectively depressed during DO-stat fed-batch operation; consequently, the solubility of anti-CRP scFv was significantly improved from 36-43% by the flask and batch cultures to 96-98% by the DO-stat fed-batch culture under a wide range of DO conditions. From the kinetic analysis of fed-batch experiments, it was also found that the successful folding of anti-CRP scFv in the cytoplasm occurred when metabolic rates, such as the specific growth rate and specific glucose consumption rate, were relatively low. These results show that the fed-batch culture operated by the DO-stat feeding strategy was effective for the enhanced production of anti-CRP scFv with high solubility.