ABSTRACT

Common but ecophysiologically unexplored Anabaena sp. strain FS 77 (Cyanoprokaryota/ Cyanophyta), isolated from oil polluted soils of southern Iran (Khuzestan province), has been characterized by a combination of extremely low irradiance (2 µE·m⁻²·s⁻¹), different pHs (5, 7, 9, 10), and inorganic carbon availability (extremely limited and relatively available). Maximum growth rates were observed at pH 9 when dissolved inorganic carbon was extremely limited. This strain has a relatively powerful carbon dioxide concentrating system which may be induced by alkaline conditions. Phycobilisomes seem more sensitive to pH than carbon dioxide concentration. The size of phycobilisomes increased, but the photosystem II to photosystem I ratio decreased significantly under neutral conditions. Extremely alkaline conditions (pH 10) caused no significant fluctuation in photosynthesis efficiency. The maximum nitrogenase activity was seen in cells grown at a pH of 9 and 10 under carbon dioxide limitation. The pattern of nitrogenase activity was more or less the same under photosynthesis. Sugar and protein content decreased at pH 10 compared to pH 9. Carotenoid content was not affected by pH and carbon dioxide fluctuations. Cylindrical heterocysts were the main form found but may be transformed to sub-cylindrical and oval-cylindrical at pH and carbon dioxide fluctuations. Collectively, results indicate that Anabaena sp. FS77 shows the ability to acclimate growth, excretion behavior, photosynthetic apparatus, and nitrogen fixation machinery operation at combined variations of pH and carbon dioxide under extremely limited irradiance in the range usually found in oil polluted soils of southern Iran.