Abstract
A study was made of the effects of environmental factors on the development and control of hydrogen production in the marine blue-green alga Miami BG 7 Oscillatoria sp. 000701.The production of cellular biomass capable of evolving hydrogen gas was strongly effected by light intensity, temperature, and the input of ammonia as a nutrient. Given ideal temperature and light conditions Miami BG 7 is a fast growing (i.e., 9hrs/doubling) cyanobacteria capable of generating substantial biomass (i.e., 250 mg dry weight/liter). It is also characterized by tolerance to a broad range of salinities (i.e., near optimal growth from 2.5 to 35('o)/oo) and a resistence to high temperature (i.e., lethal temperature of 46(DEGREES)C).One of the most critical aspects of environmental regulation is the depletion of combined nitrogen from the growth media, which is a prerequisite for the initiation of hydrogen production. The achievement of maximum hydrogen producing capability appears to coincide with the depletion of internal nitrogen reserves. The timing of peak activity is strongly dependent on temperature and light intensity because of the impact of these factors on growth and nitrogen depletion.The hydrogen production process exhibits greater flexibility to environmental extremes than growth. The rate of production saturates at low light intensities and no photoinhibition is observed at high light intensity (i.e., 1000 (mu)Einsteins/m('2)/sec.). As in the case of growth hydrogen production is tolerant to high temperatures (i.e., 1/2 of the saturating rate at 42.5(DEGREES)C) and shows no adverse response to salinities ranging from 2.5 to 35('o)/oo.The inhibition of hydrogen production by photosynthetically produced oxygen was studied. The capacity of cells to evolve oxygen photosynthetically deteriorates rapidly during nitrogen depletion. Cells capable of active hydrogen production exhibit only a fraction of their maximum oxygen evolving capacity. In addition the ability of these cells to produce oxygen in closed anaeorobic hydrogen production systems is short-lived. Finally the maintenance of high temperatures in production systems not only enhances the rate of hydrogen evolution but increases respiration and the oxygen compensation light intensity. Taken together these three facts open up new options for the avoidance of oxygen inhibition.In the last phase of this research the response of hydrogen production to light quality was studied. Hydrogen production responds best to red light. But the specific reaction of cells to different parts of the spectrum depends on the age of the cells used in the assay. The results of action spectra, DCMU and enhancement studies with Miami BG 7 indicate that hydrogen production based on a two photosystem reaction may exist at the early stages of hydrogen producing capability. A two photosystem hydrogen production reaction has not been reported in other studies of blue-green algae.