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要旨:
A circular economy requires the re-valorization of waste products. Since the beginning of the industrial age, one of the major emissions of human civilization has been CO2. While it could be regarded simply as a pollutant, it is, intrinsically, a resource – not only a carbon source, but also the main carbon source supporting all life on the planet. While it is sensible to use it as such, its chemical conversion into useful compounds is challenging – while nature has evolved pathways for its assimilation for millions of years. Biological systems for CO2 valorization have therefore come into focus. In addition to CO2, other one-carbon (C1) compounds, in particular methanol and formate, have been suggested for electro-biochemical applications. In these two-step processes, C1 compounds are generated by electrochemical hydrogenation of CO2 and subsequently utilized by biological platform organisms as a source of both carbon and reductive power. Out of the C1 compounds, formate is biologically assimilated at the highest energetic efficiency. Natural formate assimilations, however, is limited to specialist microbes that can be challenging to cultivate or genetically modify. The generation of synthetic formatotrophs, therefore, offers the potential of broadening the scope to more commonly used platform organisms such as E. coli. Here, two modes of action can be followed – one, the transposition of natural formate assimilation pathways and two, the generation of fully synthetic pathways for formate assimilation. In this thesis, two modules for synthetic formate assimilation are developed through rational enzyme engineering. First, a module for the reduction of formate to formaldehyde via formyl phosphate is created, permitting integration of formate into otherwise methanol-assimilating pathways. Second, a novel carboligase is designed that is able to condense formaldehyde with formyl-CoA, an activated formate species, into the C2 compound glycolyl-CoA. The combination of these two modules displays a potential for formate assimilation into a C2 compound at higher efficiency than previously published routes. In summary, this thesis enriches the scope of synthetic formatotrophy by two powerful building blocks that enable new paths in carbon metabolism.
