Optimization of conditions for photoproduction of ammonia from nitrate by Anacystis nidulans

Abstract

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 (micromolar) 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 CO2 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.