CoConut: Cell-cell interaction in a synthetic co-culture, PHA production from sunlight and CO₂ in an artifical co-culture between Synechococcus elongatus and Pseudomonas putida

Most biotechnological processes employ bacteria that metabolize carbohydrates in order to generate the desired product. In these conventional production processes, the cost of the carbohydrate feedstock may be a significant fraction of the total production cost. Furthermore, the carbohydrate feedstock is often derived from agricultural production, thereby wasting farmland that could otherwise be used for food production. Therefore, there is great interest to replace traditional, crop-based feedstocks like sugarcane, corn, and wheat by carbohydrates derived from eukaryotic algae and cyanobacteria. This brings along many advantages: these new sources of feedstock can be produced on non-arable land, salty or brackish water freeing up farmland for the production of food. Moreover, the microbial efficiency for the conversion of captured solar energy into biomass exceeds that of terrestrial plants. At the same time, global warming is combatted as CO₂ is captured in chemical compounds. Unfortunately, the intrinsic capacities of photosynthetic microbes for the production of interesting compounds are limited and efficiencies are low.

The aim of the CoConut project is to overcome this bottleneck by using and understanding the characteristic of a synthetic co-culture under controlled conditions, in which sugar production by a photosynthetic organism is directly coupled to the growth of a heterotrophic production strain (see graphical abstract). The proof of concept was shown recently by our group (see PHA from CO2 and sunlight in a defined co-culture). This engineered mixed culture allows us to perform functions, that are difficult to program in individual cells. Additionally, both strains are genetically modified to perform their individual task in an optimal way. The division of labour of specialist species resembles the situation found in natural microbial consortia and can lead to a higher catalytic activity and stability compared to a monoculture. In the artificial co-culture the photosynthetic strain (upstream strain), here S. elongatus PCC7942, provides the substrate for the heterotrophic downstream strain, here Pseudomonas putida EM173. The cyanobacterium fixes CO₂ through photosynthesis and secretes sufficient sucrose to support the growth of P. putida, which has been genetically engineered to metabolise sucrose as the only carbon source. The downstream strain can either be used directly for the production of interesting compounds by exploiting intrinsic biotechnological properties (e.g. PHA production in case of P. putida) as it is the case in this proposed project, or can be understood as chassis, in which the genetic information for the production of the desired products is introduced.

Former project supervision: M.Sc. Franziska Kratzl