Sustained Photoproduction of Ammonia from Nitrate by Anacystis nidulans

Sustained Photoproduction of Ammonia from Dinitrogen and Water by the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain ATCC 33047

Conditions have been developed that lengthen the time during which photosynthetic dinitrogen fixation by filaments of the cyanobacterium Anabaena sp. strain ATCC 33047 proceeds freely, whereas the subsequent conversion of ammonia into organic nitrogen remains blocked, with the resulting ammonia released to the outer medium. When l-methionine-dl-sulfoximine was added every 20 h, maximal rates of ammonia production (25 to 30 mumol/mg of chlorophyll per h) were maintained for about 50 h. After this time, ammonia production ceased due to a deficiency of glutamine and other nitrogenous compounds in the filaments, conditions which finally led to cell lysis. The effective ammonia production period could be further extended to about 7 days by adding a small amount of glutamine at the end of a 40-h production period or by allowing the cells to recover for 8 h in the absence of l-methionine-dl-sulfoximine after every 40-h period in the presence of the inhibitor. A more prolonged steady production of ammonia, lasting for longer than 2 weeks, was achieved by alternating treatments with the glutamine synthetase inhibitors l-methionine-dl-sulfoximine and phosphinothricin, provided that 8-h recovery periods in the absence of either compound were also alternated throughout. The biochemically manipulated cyanobacterial filaments thus represent a system that is relatively stable with time for the conversion of light energy into chemical energy, with the net generation of a valuable fuel and fertilizer through the photoreduction of dinitrogen to ammonia.

Optimization of Conditions for Photoproduction of Ammonia from Nitrate by Anacystis nidulans

The effect of several relevant environmental factors influencing the photoproduction of ammonia from nitrate by Anacystis nidulans cells treated with the glutamine synthetase inhibitor l -methionine- dl -sulfoximine has been investigated. The optimal ratio between l -methionine- dl -sulfoximine concentration (micro-molar) and cell density (micrograms of chlorophyll per milliliter) was around 1, the process taking place at maximal rate at a temperature of about 40°C, within the pH range of 7 to 10. Ammonia production was stimulated by CO 2 or bicarbonate and was not affected by the accumulation of ammonia in the medium up to concentrations of 30 mM. The rate of ammonia production was found to be determined by the interaction of at least four factors, namely, irradiance and the density, depth, and turbulence of the cell suspension. Ammonia photoproduction from nitrate and water represents an interesting process for the conversion of light energy into chemical energy, which can operate at high efficiency, around 30% of its theoretical maximum.