Fig 1.

Genotype and growth of Anabaena PCC 7120 wild type, amiC mutants SR477 andSR478, and complemented mutant SR477(pIM496) with different N sources. (A) Genomic organization of the amiC cluster in Anabaena PCC 7120 wild type (WT), amiC1 mutant strain SR477, and amiC2 mutant strain SR478. (B) Growth of pseudocolonies with and without NO₃⁻: after nitrogen step-down, filaments were resuspended in BG11 (containing NO₃⁻) or BG11₀ medium, and suspensions containing 100 ng chlorophyll were spotted on top of agar with (upper part) or without (lower part) NO₃⁻ and incubated under growth conditions for several days. (C) Light and autofluorescence microscopy images of Anabaena PCC 7120 wild type and amiC mutants SR477 and SR478 grown on BG11 at 0 h and 48 h after nitrogen step-down. BF, bright field; AF, autofluorescence. (D) Heterocyst frequency of Anabaena PCC 7120 wild type and mutant strains SR477, SR478, and SR477(pIM496). To calculate the frequency, 2,000 cells were counted. Bar = 10 μm.