Temperature stress and oxygen inhibition of nitrogen fixation in a Nostoc cyanobacterium

Abstract

The effect of elevated temperature and oxygen concentration on nitrogen fixation was investigated in a Nostoc species previously isolated in Java, Indonesia. This organism grows well under nitrogen-fixing conditions at 25°C and also adapts to grow at 40°C. Cells grown at these temperatures responded differently to thermal stress at 48°C; cells grown at 25°C and stressed without oxygen at 48°C were subsequently much more sensitive to oxygen than cells grown at 40°C. This indicates an adaptation of the cells to growth at the higher temperature. In the presence of an adequate supply of CO₂, oxygenic photosynthesis in the vegetative cells was not impaired by the thermal stress, nor was whole cell respiration. The addition of H₂ substantially overcame the oxygen-inhibition for adapted cells but not for those grown at 25°C. Possible causes of the thermal inactivation of nitrogen fixation are discussed.