This bacterial population behavior could be maintained up to about 15 bacterial cell generations, until faster-growing and nonammonium excreting cells arose at an apparent high frequency. This tuning was in accordance with the intensity of the previous induction of GS accumulation in the cells.

The final bacterial population, and timing and magnitude of algal N-biofertlization was finely tuned in a deferred manner. Further dilution of GS by cell division slowed-down growth, promoted ammonium-excretion and cross-fed algae. After switching cells overaccumulating GS into a noninducing medium, they proliferated for several generations at the expense of the previously accumulated GS. Here we studied the dynamic algal cross-feeding properties of a genetically-modified Azotobacter vinelandii strain which can be tuned to over-accumulate different levels of glutamine synthetase (GS, EC 6.3.1.20) under the control of an exogenous inducer. Some of these strains also cross-feed ammonium into microalgae raising additional concerns on their sustainable use in agriculture due to the potential risk of producing a higher and longer-lasting eutrophication problem than synthetic N-fertilizers. Genetically-optimized bacteria for ammonium release have an improved biofertilization capacity. There is an increasing interest in the use of N2-fixing bacteria for the sustainable biofertilization of crops.

Strong but transient ammonium cross-feeding of microalgae.GS-dependent deferred control of bacterial growth and ammonium release.Ammonium-excreting bacteria are potential eutrophication agents.Deferred control of ammonium cross-feeding in a N2-fixing bacterium-microalga artificial consortiumР”В®nvironmental biotechnology, Published: 09 March 2021, 2021

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