Enhanced extracellular ammonium release in the plant endophyte Gluconacetobacter diazotrophicus through genome editing

The plant growth-promoting bacterium Gluconacetobacter diazotrophicus was originally discovered in association with sugarcane plants as an endophyte. As a member of the small class of organisms definedas diazotrophs, G. diazotrophicus is capable of fixingnitrogen from the atmosphere and could serve an important role in minimizing the requirements for nitrogen from industrial-derived fertilizers. In addition to sugarcane, G. diazotrophicus is capable of forming endophyte associations with a variety of other important crops. It has been reported that this microbe requires micro-aerobic conditions to effectivelyfixnitrogen gas from the atmosphere through the enzyme nitrogenase, making it slightly more difficultto study the diazotrophic lifestyle in the laboratory. The ability of the strain to reside within the plant during growth means that any extracellular nitrogen released by this microbe would immediately become available to the plant host. For this reason, it is an ideal target for development as an improved biofertilizer strain. In this work, we constructed strains of G. diazotrophicus that result in enhanced ammonium release, as measured by growing with a closely associated algal strain under micro-aerobic conditions, and by further quantifying ammonium concentrations accumulated under micro-aerobic and aerobic growth.