**Abstract**

Methanotrophic bacteria can use methane as their only energy and carbon source, and they can be deployed to manufacture a broad range of value-added materials, from single-cell protein (SCP) for feed and food applications over biopolymers, such as polyhydroxybutyrate (PHB), to value-added building blocks and chemicals. SCP can replace fish meal and soy for fish (aquacultures), chicken, and other feed applications, and also become a replacement for meat after suitable treatment, as a sustainable alternative protein. Polyhydroxyalkanoates (PHA) like PHB are a possible alternative to fossil-based thermoplastics. With ongoing and increasing pressure toward decarbonization in many industries, one can assume that natural gas consumption for combustion will decline. Methanotrophic upgrading of natural gas to valuable products is poised to become a very attractive option for owners of natural gas resources, regardless of whether they are connected to the gas grids. If all required protein, (bio) plastics, and chemicals were made from natural gas, only 7, 12, 16–32%, and in total only 35–51%, respectively, of the annual production volume would be required. Also, that volume of methane could be sourced from renewable resources. Scalability will be the decisive factor in the circular and biobased economy transition, and it is methanotrophic fermentation that can close that gap.

**Keywords:** methanotroph, biopolymers, polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), single-cell protein (SCP), value-added chemicals, feed, food, scalability
