Exploring and exploiting yeast volatile metabolites

Mengers, Hendrik Gerhard; Blank, Lars M. (Thesis advisor); Jupke, Andreas (Thesis advisor)

1. Auflage. - Aachen : Apprimus Verlag (2023)
Book, Dissertation / PhD Thesis

In: Applied microbiology 30
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2023

Abstract

The sensation of "smell", caused by volatile organic compounds, is native to all domains of life. The sum of all emitted molecules is called the volatilome but this is a sparsely populated research field. Saccharomyces cerevisiae is a common host for modern biotechnology and has been used for biotechnological production of ethanol for most of human civilisation, but still, the gas phase above fermentations is yet to be fully understood. This thesis aims to contribute to the knowledge of different aspects of the yeast volatilome. Carbon dioxide, even with the current fight against human-made climate change, is an often neglected metabolite. Through complementing a bioethanol fermentation in an overpressure reactor with a Ru-catalyst in an organic phase and high hydrogen pressure, carbon dioxide was converted to formic acid. With optimised reaction parameters, over 26 % of the greenhouse gas were converted to the non-volatile, nontoxic,C1-source formate. Biotechnological production processes often suffer from high downstream purificationcosts, which could be minimised through the targeted overproduction of volatile metabolites. One prime example is acetaldehyde, with a worldwide production of over 1 Mt/a, which is chiefly synthesised from petrochemical feedstocks. S. cerevisiae with completely deleted alcohol dehydrogenase activity was used to produce acetaldehyde from glucose at rates of up to 100 mg/g/h in up to 750 mL scale. Because of the compound’s low boiling point, it is inevitably stripped from the reactor. For this in situ separation, water traps were designed to trap the acetaldehyde from the off-gas. As a new method for volatile and volatilome analysis, SESI-Orbitrap MS was established on the example of the heat-labile allicin from garlic. This compound was measured from a microreaction tube with a solution of synthetic allicin, freshly crushed garlic, and from human breath after garlic consumption. Further, the differences between different Allium species were examined, showing the versatility of this measurement methodology. Lastly, the complete volatilome was measured online with a time resolution of0.4 Hz from the off-gas of a yeast fermentation. While the ethanol signal showed high agreement to standard measurement techniques, acetaldehyde as an example of low-abundance high-volatile compounds, was measured hours earlier. In over 16,000scans, over 200 compounds were identified by their molecular formula, each with their unique intensity over time profile. Two metabolic shifts were visible, and, for example, the production of medium-chain fatty acid ethyl esters was shown uniquely in the transition period during the C-source shift. In conclusion, diverse aspects of the yeast volatile space were examined: omitting unwanted volatiles, overproducing valuable volatiles, and finding new methods to analyse volatiles.

Institutions

• Department of Biology [160000]
• Chair of Applied Microbiology [161710]