CO2 fixation in extreme conditions

Both in society and industry awareness is raising that a transition from petrochemical industry towards more sustainable bio-based processes is urgent. In this context, the use of microorganisms with autotrophic metabolism as cell factories for the direct conversion of CO 2 into high-added value chemicals or fuels is a promising approach. Recently, a unique autotrophic CO 2 fixation pathway was discovered in thermoacidophilic archaea, growing optimally at industrially relevant conditions of high temperature and low pH. While the genetically amendable and industrially promising species Sulfolobus acidocaldarius encodes the pathway genes, it has lost the capability to fix CO 2 . Here, we will investigate the factors that have caused this loss: either one or several pathway enzymes are dysfunctional, or the expression and transcriptional regulation of the pathway is defect. Omics- methods will be combined with detailed biochemical analyses to generate deep insights into the functioning of the pathway. These insights will be used for the re-engineering of CO2 fixation in S. acidocaldarius by restoring the identified defects, followed by bioprocess engineering for pilot scale autotrophic growth. This project aims to develop an efficient microbial CO 2 fixation process working in extreme conditions. Furthermore, fundamental insights into the functioning of the 3- hydroxypropionate/4-hydroxybutyrate cycle as well as in its transcriptional regulation will be generated.

In this joint FWO-FWF project, performed by the partners TU Wien (TUW) and Vrije Universiteit Brussel (VUB), the understanding of extremophilic organisms and their respective bioprocessing was enhanced and several applications of two members of the order Sulfolobales, namely S. acidocaldarius and Metallosphaera sedula, were studied. We present the first ever detailed physiological characterization of S. acidocaldarius in a controlled, continuously performed bioreactor environment on different substrates. We successfully developed an urgently needed method to determine the viability of these extremophiles. We investigated the effect of oxygen on these special organisms and successfully scaled up a bioreactor cultivation process from 2 L to 200 L. We analyzed the special tetra-ether lipids of these organisms, for which we developed an unprecedented analytical method, and used them to generate novel liposomes and lipid nanoparticles, which we analyzed in detail. These lipids present highly interesting building blocks for future medical applications. We also developed a novel, defined cultivation medium for M. sedula, allowing more detailed basic research with this organism in the future. Finally, we also elucidated the overflow metabolism of S. acidocaldarius - a yet unknown phenomenon in the scientific community. The scientific outcome of this successful project have been 6 peer-reviewed published scientific papers and 1 accepted manuscript.