Effect of PelB signal sequences on Pfe1 expression and ω-hydroxyundec-9-enoic acid biotransformation in recombinant Escherichia coli

Systematic Engineering of Escherichia coli for Efficient Production of Pseudouridine from Glucose and Uracil

In this study, we proposed a biological approach to efficiently produce pseudouridine (Ψ) from glucose and uracil in vivo using engineered Escherichia coli. By screening host strains and core enzymes, E. coli MG1655 overexpressing Ψ monophosphate (ΨMP) glycosidase and ΨMP phosphatase was obtained, which displayed the highest Ψ concentration. Then, optimization of the RBS sequences, enhancement of ribose 5-phosphate supply in the cells, and overexpression of the membrane transport protein UraA were investigated. Finally, fed-batch fermentation of Ψ in a 5 L fermentor can reach 27.5 g/L with a yield of 89.2 mol % toward uracil and 25.6 mol % toward glucose within 48 h, both of which are the highest to date. In addition, the Ψ product with a high purity of 99.8% can be purified from the fermentation broth after crystallization. This work provides an efficient and environmentally friendly protocol for allowing for the possibility of Ψ bioproduction on an industrial scale.

Pseudomonas putida as a platform for medium-chain length α,ω-diol production: Opportunities and challenges

Medium-chain-length α,ω-diols (mcl-diols) play an important role in polymer production, traditionally depending on energy-intensive chemical processes. Microbial cell factories offer an alternative, but conventional strains like Escherichia coli and Saccharomyces cerevisiae face challenges in mcl-diol production due to the toxicity of intermediates such as alcohols and acids. Metabolic engineering and synthetic biology enable the engineering of non-model strains for such purposes with P. putida emerging as a promising microbial platform. This study reviews the advancement in diol production using P. putida and proposes a four-module approach for the sustainable production of diols. Despite progress, challenges persist, and this study discusses current obstacles and future opportunities for leveraging P. putida as a microbial cell factory for mcl-diol production. Furthermore, this study highlights the potential of using P. putida as an efficient chassis for diol synthesis.

Characterization of Putative Virulence Factors of Pseudomonas aeruginosa Strain RBS Isolated from a Saltern, Tunisia: Effect of Metal Ion Cofactors on the Structure and the Activity of LasB

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. P. aeruginosa can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated P. aeruginosa strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. β-Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.