Microbial mutualisms play critical roles in a diverse number of ecosystems and have the potential to improve the efficiency of bioproduction for desirable chemicals. We investigate the growth of a photosynthetic cyanobacterium, Synechococcus elongatus PCC 7942, and a diazotroph, Azotobacter vinelandii, in coculture. From initial studies of the coculture grown in media with glutamate, we proposed a model of cross-feeding between these organisms. We then engineer a new microbial mutualism between Azotobacter vinelandii AV3 and cscB Synechococcus elongatus that grows in the absence of fixed carbon or nitrogen. The coculture cannot grow in the absence of a sucrose-exporting S. elongatus, and neither organism can grow alone without fixed carbon or nitrogen. This new system has the potential to produce industrially relevant products, such as polyhydroxybutyrate (PHB) and alginate, from air, water, phosphate, trace metals, and sunlight. We demonstrate the ability of the coculture to produce PHB in this work.
Keywords: cyanobacteria; diazotroph; engineered coculture; metabolic syntrophy.