Engineering microbial hosts for the production of aromatic compounds

With the global population surpassing 8 billion individuals, there has been a parallel increase in demand for indispensable commodities like fuels, food, and consumer goods. Aromatic compounds play an integral role in these essential commodities, as they are widely utilized in pharmaceuticals, food ingredients, flavorings, cosmetics, and plastic precursors. However, aromatic compounds are typically sourced from non-sustainable sources, causing environmental destruction and contributing to climate change.

Biotechnological production utilizing microbial cell factories has emerged as a promising alternative for manufacturing aromatic compounds, enabling the conversion of renewable substrates into a diverse array of high-value aromatics. However, this approach faces certain limitations that hinder its widespread implementation for larger-scale production of compounds. This thesis focuses on investigating and addressing some of these challenges, aiming to provide solutions for improved utilization of biotechnological systems in aromatic compound production.

We first explore the use of the oleaginous yeast Yarrowia lipolytica for the production of aromatic compounds, as an alternative to Escherichia coli and the baker’s yeast Saccharomyces cerevisiae, the conventional hosts typically engineered for the production of aromatics in literature. We demonstrate high-level production of the plant antioxidant resveratrol with limited genetic engineering, showing the potential of Y. lipolytica for the production of these compounds.

Next, we investigate in vivo halogenation of the aromatic amino acid L-tryptophan by the expression of tryptophan halogenases. We show how L-tryptophan can be halogenated at different positions of the molecule with either chlorine or bromine, and how these can be decarboxylated into halogenated tryptamine, precursor for a wide range of compounds with pharmaceutical applications.

Another topic researched is the toxicity of aromatic compounds against common production hosts, as many of these products are naturally produced by plants as a defense mechanism against microbes. We perform a systematic analysis of the toxicity of over 50 aromatics in multiple production hosts and use a transporter deletion library to investigate transporters that affect product tolerance and might be involved in transport mechanisms.

These findings present avenues for further exploration and innovation in developing sustainable and efficient microbial cell factories to produce valuable aromatic compounds.