FIG. 4.

Growth of strains CSRL16 and CSRL17 with different N sources. (A) Cell suspensions of Anabaena sp. strains PCC 7120, CSRL16, and CSRL17 grown with ammonium (with antibiotics in the case of the mutants) and washed with combined-nitrogen-free medium were used to inoculate (10 ng Chl per spot) plates of BG11 medium (NO₃⁻) or of BG11₀ medium supplemented (NH₄⁺) or not (N₂) with ammonium that were incubated for 14 days under culture conditions (see Materials and Methods for details). (B) Cell suspensions of Anabaena sp. strains PCC 7120, CSRL16, and CSRL17 grown with ammonium (and antibiotics in the case of the mutants) and washed with combined-nitrogen-free medium were used to inoculate liquid cultures with the indicated N source, which were incubated under culture conditions. The numbers are specific growth rate constants (day⁻¹) and are the averages from two independent experiments with similar results.