The use of elements of the E. coli Ntr-system for the design of an optimized recombinant expression system for high cell density cultivations

RpoN-Based stapled peptides with improved DNA binding suppress Pseudomonas aeruginosa virulence

Stapled peptides have the ability to mimic α-helices involved in protein binding and have proved to be effective pharmacological agents for disrupting protein-protein interactions. DNA-binding proteins such as transcription factors bind their cognate DNA sequences via an α-helix interacting with the major groove of DNA. We previously developed a stapled peptide based on the bacterial alternative sigma factor RpoN capable of binding the RpoN DNA promoter sequence and inhibiting RpoN-mediated expression in Escherichia coli. We have elucidated a structure-activity relationship for DNA binding by this stapled peptide, improving DNA binding affinity constants in the high nM range. Lead peptides were shown to have low toxicity as determined by their low hemolytic activity at 100 μM and were shown to have anti-virulence activity in a Galleria mellonella model of Pseudomonas aeruginosa infection. These findings support further preclinical development of stapled peptides as antivirulence agents targeting P. aeruginosa.

Adaptastat—a new method for optimising of bacterial growth conditions in continuous culture: Interactive substrate limitation based on dissolved oxygen measurement

A new method for continuous cultivation of microbes, called adaptastat, is described. It involves automatic adaptation of microbial cultures to their maximum feeding rates and avoids substrate accumulation. The state of the culture is estimated at intervals by briefly (and markedly) decreasing the substrate feeding rate and measuring, via the dissolved oxygen response, the time taken to exhaust the residual substrate. The method has been exemplified by cultivating Escherichia coli on single carbon sources (glucose, acetate, succinate, and fully deuteriated medium based on deuteriated succinate) and also by simultaneous limitation of two feeding channels (succinate/acetate and glucose/ammonium chloride). Several possible applications of the adaptastat technology are presented. The method provides an efficient means of labelling microbial components and products with stable isotopes. In particular, adaptastat technology can be used to adapt disabled bacterial strains to the use of simple, inexpensive substrates. It can also be used more generally in the study of microbial cell cultures, for example for the determination of maximum specific growth rates and the stoichiometric ratio of utilisation of two nutrients in conditions of simultaneous limitation.

Understanding the art of producing protein and nonprotein molecules in Escherichia coli

The high-level production of functional proteins in E. coli is a very extense field of research in biotechnology. A number of important aspects to be considered in the initial design of an expression system and their interplay, were clear years ago. However, in recent times, strategies that go beyond transcription, translation, stability, vector, and strain choice, have been developed; so now expression of active peptides can be viewed as a more integrated process. Coexpression of protein subunits, foldases and chaperones, protein folding, location and purification schemes, metabolic engineering of the cell's central metabolism, and in vitro refolding strategies, are some of the novelties that are now available to aid in the success of an efficient expression system for active heterologous proteins. This review presents a compilation of the basic issues that influence the success in the production of protein and nonprotein products in Escherichia coli, as well as some general strategies designed to facilitate downstream process operations and improve biosynthesis yields.