Influence of nitrogen on the growth and morphology of cyanobacteria, Anabaena sp.

Cyanobacteria are the primary culprits responsible for deteriorating the health of aquatic ecosystems in lakes or rivers. Nitrogen concentration is a crucial factor affecting the synthesis of cellular contents, which, in turn, influence the growth of cyanobacteria. This study focused on the growth and morphological characteristics of Anabaena sp., a representative filamentous cyanobacteria, depending on nitrate concentrations varying from 0.5 to 20.0 mg N/L. As the nitrate concentration increased, the filament density, optical density (OD680), cellular protein content proportionally increased. While growing, both nitrate and phosphate concentration depleted, notably affecting the cell compositions in filament: akinete, vegetative, and heterocyst cell. When nitrate concentration was exhausted, the heterocyst cell density of Anabaena sp. increased to supplement nitrogen through nitrogen fixation, whereas vegetative cell density kept increasing as long as nitrate remained. Morphological changes in akinete and heterocyst cells in Anabaena sp. were less affected by nitrogen concentration, whereas those in vegetative cells were affected by both growth state and nitrogen concentration. The close relationship between heterocyst cells and nitrogen concentration suggests that heterocyst cell can be used to characterize Anabaena growth responding to nitrogen loading, as well as provide an important information on nitrogen level affecting Anabaena bloom potential.