Abstract
Nitrogen is globally limiting primary production in the ocean, but some species of cyanobacteria can carry out nitrogen (N) fixation using specialized cells known as heterocysts. However, the effect of N sources and their availability on heterocyst development is not yet fully understood. This study aimed to evaluate the effect of various inorganic N sources on the heterocyst development and cellular growth in an N-fixing cyanobacterium, Anabaena variabilis. Growth rate, heterocyst development, and cellular N content of the cyanobacteria were examined under varying nitrate and ammonium concentrations. A. variabilis exhibited high growth rate both in the presence and absence of N sources regardless of their concentration. Ammonium was the primary source of N in A. variabilis. Even the highest concentrations of both nitrate (1.5 g L−1 as NaNO3) and ammonium (0.006 g L−1 as Fe-NH4-citrate) did not exhibit an inhibitory effect on heterocyst development. Heterocyst production positively correlated with the cell N quota and negatively correlated with vegetative cell growth, indicating that both of the processes were interdependent. Taken together, N deprivation triggers heterocyst production for N fixation. This study outlines the difference in heterocyst development and growth in A. variabilis under different N sources.
Highlights
Cyanobacteria can survive in harsh environmental conditions such as darkness, extreme temperatures, and high salinity
This study evaluated the changes in cell growth, heterocyst development, and N cell quota in a cyanobacterial species, A. variabilis, under various concentrations of nitrate and ammonium over 14-d laboratory incubation
This study demonstrated that a filamentous cyanobacteria, Anabaena variabilis, developed heterocysts in response to N availability
Summary
Cyanobacteria can survive in harsh environmental conditions such as darkness, extreme temperatures, and high salinity. They have the ability to grow under nutrient limitations [1,2]. Cyanobacterial blooms could be controlled by reducing nutrient input, especially nitrogen (N) and phosphorus (P), which in turn leads to the reduction in their growth and development [6,7]. P deprivation is more effective in controlling cyanobacterial blooms than N deprivation. N deprivation exhibits inhibitory effect only on non-N-fixing taxa, leaving N-fixing taxa less or unaffected owing to their ability to fix N for survival [8]
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