Methods for Generating Microbial Cocultures that Grow in the Absence of Fixed Carbon or Nitrogen

This work is motivated by both (1) the desire to make interesting products without the reliance on fixed carbon or fixed nitrogen using microbial cocultures, and (2) the desire to develop new methods for growing microbial communities. The bioplastic polyhydroxybutyrate (PHB), for example, is considered prohibitively expensive to make from sugar (compared to polypropylene). Utilizing and building on engineered strains of Synechococcus elongatus and Azotobacter vinelandii, we have combined a nitrogen-fixing organism with a carbon-fixing organism to make PHB from air, water, sunlight, and trace minerals. Our observations of coculture growth in batch culture led us to develop an improved system based on manipulating the osmotic pressure within a hydrogel. The methods we used to develop this coculture are described in detail in the following chapter, including notes detailing some of our additional observations or thoughts on this system.