Isolation and characterization of Anacystis nidulans R2 mutants affected in nitrate assimilation: Establishment of two new mutant types

Summary Eighteen mutant strains of the unicellular cyanobacterium Anacystis nidulans R2 that are unable to assimilate nitrate have been isolated after transposon Tn901 mutagenesis. Characterization of phenotypes and transformation tests have allowed the distinction of five different mutant types. The mutants exhibiting a nitrate reductase-less phenotype were identified as being affected in previously defined loci, as they could be transformed to the wild type by one of the plasmids pNR12, pNR63 or pNR193, which contain cloned genes of A. nidulans R2 involved in nitrate reduction. The mutations in strains FM2 and FM16 appear to affect two other genes involved in nitrate assimilation. Strain FM2 apparently bears a single mutation which results in both lack of nitrite reductase activity and loss of ammonium-promoted repression of nitrate reductase synthesis. FM16 has a low but significant level of nitrate reductase that is also freed from repression by ammonium, and an increased level of nitrite reductase activity. FM16 exhibited properties which indicate that this mutant strain might also be affected in the transport of nitrate into the cell.Abbreviations EDTA ethylenediamine-tetraacetic acid - MTA mixed alkyltrimethylammonium bromide - TES N-tris (hydroxymethyl)methyl-2-aminoethane sulfonic acid - Tricine N-2-hydroxy-1,1-bis (hydroxymethyl)ethyl]-glycine - Tris Tris(hydroxymethyl)aminomethane