THE EFFECT OF TEMPERATURE ON THE SENSITIVITY OF NITROGENASE TO OXYGEN IN THE CYANOBACTERIA ANABAENA-CYLINDRICA (LEMMERMANN) AND GLOEOTHECE (NAGELI)

Transient exposure to elevated temperature (37-40-degrees-C) inhibited N2 fixation (acetylene reduction) in cultures of the heterocystous cyanobacterium Anabaena cylindrica (Lemmermann) ATCC 27899 and the unicellular, nonheterocystous cyanobacterium Gloeothece sp. (Nageli) ATCC 27152. In neither organism was inhibition of N2 fixation due to thermal inactivation of nitrogenase. Rather, inactivation of N2 fixation at elevated temperature was a consequence of increased sensitivity to inhibition by O2. In A. cylindrica, thermally induced inactivation of N2 fixation by O2 could be correlated with inhibition of uptake hydrogenase. However, in Gloeothece, inhibition of carbon-supported respiratory O2 consumption by elevated temperature was the probable cause of the increased sensitivity of N2 fixation to O2.