Microbial cell factories like specialized bacteria, yeast and fungi, are used to produce relevant compounds and engineered biomolecules such as commodities, fine chemicals, food ingredients and biopharmaceuticals. Tailor-made robust microorganisms displaying novel biological behaviors produce these products in a non-chemical way utilizing nature’s toolset, in general using renewable inputs such as glucose or industrial side streams. C1 feedstocks, such as methane, methanol, formate, CO2 and CO, have important advantages over traditional organic carbon sources like glucose. They are cheap, can be obtained from CO2 in a renewable way, do not compete as food or animal feed and do not require extensive pre-processing from complex agricultural side-streams. Implementing C1 substrates in microbial cell factories would ensure a circular carbon economy that is inherently sustainable. However, due to the relative novelty of this approach, further work will be required to have abiotic C1 substrates compete with biological feedstocks. The CiTrY project will contribute to this goal by investigating and improving transport mechanisms of the C1 substrates over outer and organelle membranes of the microbial cell factories. Underexplored proteins and proteins families will be investigated, advanced protein engineering strategies and high-throughput screening will be conducted, and a novel organelle membrane targeting approach will be developed.