Figure 4.

Rates of alkaline phosphatase activity (APA) in Halothece sp. PCC 7418 under optimal ${\mathrm{NO}}_3^{-}$ and [Low ${\mathrm{NO}}_3^{-}$] conditions. (A) End point assay of APA under optimal and [Low ${\mathrm{NO}}_3^{-}$] conditions with 2 μM of MUF-P. (B) Saturation curve, velocity (V, fmole MUF cell⁻¹ h⁻¹) vs. substrate (S, μM) under [Low ${\mathrm{NO}}_3^{-}$] in [Low ${\mathrm{P}\mathrm{O}}_4^{3-}$–Low Fe], [Low ${\mathrm{P}\mathrm{O}}_4^{3-}$–High Fe], [Medium ${\mathrm{P}\mathrm{O}}_4^{3-}$–Medium Fe], and [Medium ${\mathrm{P}\mathrm{O}}_4^{3-}$–High Fe], up to 5 μM of MUF-P. ${\mathrm{P}\mathrm{O}}_4^{3-}$ is represented as Pi. In (A,B), values are the mean and the error bar is the spanning range between the duplicate measurements. Asterisks (*) indicate significant differences (p < 0.05) between ${\mathrm{NO}}_3^{-}$ optimal and [Low ${\mathrm{NO}}_3^{-}$] conditions of the same ${\mathrm{P}\mathrm{O}}_4^{3-}$ and Fe combination treatments, by individual t student test. Different letters indicate pairwise significant differences (p < 0.05) among treatments in [Low ${\mathrm{NO}}_3^{-}$] using a post-hoc test (Bonferroni) after ANOVA over the whole dataset was done.