Biotransformation of 2,4-dinitrotoluene in a phototrophic co-culture of engineered Synechococcus elongatus and Pseudomonas putida

In contrast to the current paradigm of using microbial monocultures in most biotechnological applications, increasing efforts are being directed towards engineering mixed-species consortia to perform functions that are difficult to program into individual strains. Additionally, the division of labor between specialist species found in natural consortia can lead to increased catalytic efficiency and stability relative to a monoculture or a community composed of generalists. In this work, we have designed a synthetic co-culture for phototrophic degradation of xenobiotics, composed of a cyanobacterium, (Synechococcus elongatus PCC 7942) and a heterotrophic bacterium (Pseudomonas putida EM173). Cyanobacteria fix CO2 through photosynthetic metabolism and secrete sufficient carbohydrates to support the growth and active metabolism of P. putida, which has been engineered to consume sucrose as the only carbon source and to degrade the environmental pollutant 2,4-dinitrotoluene (2,4-DNT). The synthetic consortium is able to degrade 2,4-DNT with only light and CO2 as inputs for the system, and it was stable over time through repeated backdilutions. Furthermore, cycling this consortium through low nitrogen medium promoted the accumulation of polyhydroxyalkanoate (PHA)-an added-value biopolymer-in P. putida, thus highlighting the versatility of this production platform. Altogether, the synthetic consortium allows for simultaneous bioproduction of PHA and remediation of the industrial pollutant 2,4-DNT, using light and CO2 as inputs.\n\nImportanceIn this study, we have created an artificial consortium composed of two bacterial species that enables the degradation of the industrially-produced environmental pollutant 2,4-DNT while simultaneously producing PHA bioplastic. In these co-cultures, the photosynthetic cyanobacteria fuel an engineered P. putida strain programmed both to use sucrose as a carbon source and to perform the biotransformation of 2,4-DNT. The division of labor in this synthetic co-culture is reminiscent of that commonly observed in microbial communities and represents a proof-of-principle example of how artificial consortia can be employed for bioremediation purposes. Furthermore, this co-culture system enabled the utilization of freshwater sources that could not be utilized in classical agriculture settings, reducing the potential competition of this alternative method of bioproduction with current agricultural practices, as well as remediation of contaminated water streams.