Microbial catalysis of renewable resources into aromatics via the central metabolic precursor phenylalanine; 1. Auflage

Dissertation, RWTH Aachen University, 2020; Aachen : Apprimus Verlag, Applied microbiology 21, 1 Online-Ressource (XIII, 133 Seiten) : Illustrationen (2020). = Dissertation, RWTH Aachen University, 2020
Aromatics are versatile compounds required for numerous applications used in everyday life. Today, most aromatics are produced from crude oil in petrochemical processes, which goes along with fossil resource depletion and negative environmental impacts. Microbial catalysis can offer alternative production concepts for aromatics, in processes that utilize renewable substrates and cause less emissions. As many aromatics display enhanced toxicity towards microbes, the utilization of especially robust host cells is required to allow their efficient microbial production. Bacteria of the genus Pseudomonas thrive in challenging environments and possess the native ability to cope with many different chemicals and are thus promising candidates for the production of toxic aromatics. The aim of this thesis was the domestication of Pseudomonas species to produce various aromatic chemicals. For this, the aromatic amino acid L-phenylalanine was defined as inherent precursor. The application of rational metabolic engineering strategies, including the deletion and alteration of chromosomal elements and the overexpression of heterologous genes, resulted in Pseudomonas taiwanensis chassis strains that efficiently accumulate L-phenylalanine. The expression of a phenylalanine ammonia lyase from the plant Arabidopsis thaliana then allowed synthesis of the aromatic building block trans-cinnamate with yields of up to 48% Cmol Cmol-1using glycerol as sole carbon source. These strains were then used as platform to produce several chemical compounds of industrial interest. A ferulic acid decarboxylase led to the production of styrene, the monomer of polystyrene, which is used in different plastic products. In another approach, the plantpolyphenol pinosylvin was produced using the t-cinnamate-producing chassis strains by additional expression of a 4-coumarate ligase from Streptomyces coelicolor and a stilbene synthase from Arachis hypogaea. This work further describes the establishment of a novel pathway for the production of benzoate via enzymes of the phenylpropanoid degradation pathway of Corynebacterium glutamicum, which also allowed the production catechol and cis,cismuconatevia native pathways of Pseudomonas. In addition, a novel tool for the targeted integration of heterologous genetic elements into ribosomal operons of Pseudomonas was established. Here, the high activity of ribosomal promoters in combination with transcript-modulation by synthetic elements allowed high expression rates of foreign genes. The tool furthermore allowed analysis of the different ribosomal operons in the strain Pseudomonas putida S12. In summary, this thesis describes a rational approach towards the development of sustainable processes for the production of a variety of L-phenylalanine derived chemicals. The novel tool for heterologous gene expression delivers a further engineering approach of highly versatile Pseudomonas species, thereby bringing the application of this interesting host one step closer towards efficient industrial processes.
Published by Apprimus Verlag, Aachen