Gene sll1454 is important for growth of Synechocystis sp. PCC 6803 on nitrate as the only source of nitrogen

The gene sll1454 (narB) encodes a nitrate reductase in Synechocystis sp. PCC 6803. Deletion of sll1454 was performed by insertion of a gene coding for a neomycin phosphate transferase (npt) in both directions to the sll1454 ORF resulting in two different mutant strains named sll1454::npt direct and sll1454::npt complementary. Both strains lost the ability to grow on nitrate as the only source of nitrogen, but instead grew at the same rate as the wild type if ammonium was supplied. Trace metal replacement experiments revealed that tungsten ions inhibited the nitrate reductase in Synechocystis sp. PCC 6803, as no growth occurred with nitrate as the sole nitrogen source, if molybdenum ions were replaced equimolarly by tungsten ions. Vanadium ions, on the other hand, did not exert any negative effect under the same conditions and neither did the omission of molybdenum, tungsten or vanadium ions in the growth medium. The co-addition of molybdenum ions to cultures containing tungsten ions restored growth to the same rate as in cultures containing only molybdenum ions or none of them. Graphical abstract: (Figure presented.)