Calcium requirement in nitrogen fixation in the cyanobacterium Synechococcus RF-1

Area of Science:

• Microbiology
• Biochemistry
• Photosynthesis

Background:

• Nitrogen fixation is crucial for primary production in many ecosystems.
• Rhythmic nitrogenase activity in cyanobacteria is influenced by environmental factors.
• The role of divalent cations in nitrogenase regulation requires further elucidation.

Purpose of the Study:

• To investigate the role of calcium (Ca2+) in regulating nitrogenase activity in Synechococcus RF-1.
• To determine if Ca2+ protects nitrogenase from oxygen-induced inactivation.
• To understand the impact of Ca2+ on the diurnal rhythm of nitrogen fixation.

Main Methods:

• Utilized ethyleneglycol-bis-(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) to chelate Ca2+ and inhibit nitrogenase activity.
• Administered Ca2+ and Strontium (Sr2+) to assess their ability to restore activity.
• Manipulated oxygen levels to evaluate its interaction with Ca2+ and nitrogenase.

Main Results:

• EGTA completely blocked rhythmic nitrogenase activity.
• Ca2+ restored nitrogenase activity, with timing influencing the activity peak.
• Sr2+ partially reversed EGTA's inhibition.
• Reduced oxygen levels lessened EGTA's inhibitory effect.
• A positive correlation between Ca2+ concentration and nitrogenase activity was observed.

Conclusions:

• Ca2+ is vital for maintaining nitrogenase activity in Synechococcus RF-1.
• Ca2+ plays a protective role for nitrogenase against oxygen inactivation.
• Ca2+ influences the temporal regulation of nitrogen fixation under diurnal cycles.