A battery of bioreporters of nitrogen bioavailability in aquatic ecosystems based on cyanobacteria

Three promoters were selected to direct the expression of luxCDABE: The first, the glnA promoter, is activated in the absence of combined nitrogen. We found that it responded linearly to the addition of known amounts of combined N in the range 50-500 μM NH4+ or NO3−. The second, the nirA operon promoter, turns on in the presence of nitrate being inhibited by ammonium. The bioreporter responded linearly in the range of 10-100 μM NO3. The third, the gifA promoter, is activated in the presence of ammonium, responding linearly in the range 100-600 μM NH4+. We also used a previously described strain of Synechococcus elongatus PCC 7942 expressing glnN (glutamine synthetase type III) fused to luxAB. We found that the glnN promoter responded linearly to the addition of known amounts of N in the range 50-500 μM NH4+ or NO3−. These cyanobacterial bioreporters were tested in real environmental samples (i.e. river waters) which confirmed their validity and showed a broad spectrum response. They are therefore useful in the detection of both total N-bioavailability and specific nitrogen species.