Anaerobic conversion of a non-sugar substrate for the microbial production of chemicals

Microbial processes are currently used for food, feed and pharmaceutical markets but are too expensive for the production of chemicals and cannot compete with the petrochemical-based ones. Thanks to recent advances in –omics, metabolic engineering and genetic techniques, microorganisms can be improved, leading to the production of valuable chemicals.

Microbial production of chemicals

Microbial production of chemicals is either aerobic or anaerobic processes. In most cases, they are performed aerobically because microbial processes are mainly oxidative therefore require an electron acceptor. An easy solution is to use oxygen. Nevertheless, during aerobic fermentation, a lot of energy is produced leading to the generation of large amounts of biomass. Moreover, part of the substrate is oxidized to CO2 and the oxygen transfer rate is limiting, which contributes to lower yields and productivity. Therefore anaerobic processes are more industrially relevant but in some cases, energy generation can become a problem.

Problem description and aim of the project

Anaerobic fermentation of sugars leads to the generation of energy for the cells but starting from a non-sugar substrate, not or less. It has been shown that some bacteria are able to convert non-sugar substrates into various products, mainly acetate and propionate. Most of the time, substrate level phosphorylation (generation of ATP) is the only way for microorganisms to produce energy. Nevertheless, more-valuable chemicals can be produced after metabolic engineering of the strains.

The aim of my project is the microbial conversion of a non-sugar substrate into valuable chemicals under anaerobic conditions. Furthermore, inventive solutions have to be found to generate sufficient energy supply for cells.

Approach

The first step of the project consists of investigating microorganisms naturally able to convert our substrate under anoxic conditions, the products formed and the pathways involved. A list of interesting chemicals that can be produced from the non-sugar substrate will be drawn up, taking into account the energy supply and the redox balance. Energy generation being one of the main goal of this project, the different systems occurring in microorganisms will be investigated and the feasibility of their expression in specific organisms as well. Later, metabolic engineering will be applied to microorganisms to obtain the desired pathway. Fermentation studies will be performed under the conditions we are interested in with the modified microorganism and some parameters will be assessed such as yield, productivity or enzymatic activities. Further improvement can be done but also production of other valuable chemicals, close from the one we chose in the first place.