Fig. 1.

Transition towards electron donors and carbon sources that are not relying on arable land or fossil fuels, enabled by ‘green’ electrification of the chemical industry based on water electrolysis and carbon capture and utilization approaches. These routes can generate several electron donors and/or carbon sources such as hydrogen gas (H₂), methane (CH₄), methanol (CH₃OH), formic acid (HCOOH), acetic acid (CH₃COOH) and carbon dioxide (CO₂), which are directed to the production of several major classes of chemotrophic and phototrophic microbes and metabolisms. A simplified technology readiness level (TRL), based on the Horizon 2020 work programme definitions, indicates the highest level of maturity of the microbial protein production technology. For commercial products (TRL 5‐9), examples of brand names are indicated, and for others, indicative scientific literature sources are given (TRL 1‐4). Copyright‐free images were sourced from Freepik.com.