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The cells of Rhodospirillum rubrum and Thiocapsa roseopersicina grown in media containing glutamate and arginine, respectively, as well as under conditions of nitrogen fixation evolve H2 in the light. If the cultures were grown in media with NH4+, NO3-, urea, glutamine or asparagine, hydrogen photoevolution by the cells and acetylene reduction started after the lag-phase and proceeded at a low rate. Extracts of such cells did not display the activity of nitrogenase which could be assayed by the ATP-dependent evolution of H2 from dithionite. The data obtained confirm the fact that hydrogen photoevolution by purple bacteria involves nitrogenase whose synthesis is regulated (according to the action of glutamine) with the participation of glutamine synthetase. NH4+, glutamine and asparagine inhibit also hydrogen photoproduction by purple bacteria and acetylene photoreduction. However, they have no effect on hydrogen evolution in the dark by the cells of R. rubrum and T. roseopersicina in the presence of formiate or pyruvate, respectively, whereas carbon monoxide inhibits hydrogen production. Therefore, hydrogen production by purple bacteria in the dark must be catalyzed by hydrogenase.

The effect of various factors on the activity and biosynthesis of nitrogenase in Clostridium butyricum was estimated by the rate of acetylene reduction at different growth phases in the static culture. The activity of nitrogenase was found to be low in vegetative cells; it increased and reached the maximum at the stage of prospore formation and decreased in the course of sporulation. The duration of different stages in the cell growth cycle depended on temperature and the composition of the medium. An increase in the rate of nitrogenase synthesis at the stage of prospore formation was favoured by the presence of sodium acetate or yeast autolysate in the medium; ammonium chloride inhibited the mechanism of nitrogenase biosynthesis. Cytoplasmic membranous structures such as tubular-vesicular or lamellar mesosomes were formed in active nitrogen fixing cells grown in a medium with yeast autolysat. Such structures were absent from cells with a low activity grown in a medium containing ammonium chloride.

The effect of zinc and cobalt chlorides on cellular growth, N2 fixation, photosynthesis and changes in the content of Na+ and K+ ions in cells was studied with the blue-green alga (cyanobacterium) Anabaena spheroides. The cells were most susceptible to the action of cobalt ions at the beginning of the logarithmic growth phase, and least sensitive by the end of the phase. Cobalt ions were more toxic than zinc ions. The salts of heavy metals inhibited active transport of ions into the algal cells.

Increasing concentrations of penicillin and streptomycin inhibited the growth of the blue-green alga Nostoc linckia. Although the alga could build up resistance to higher concentrations of penicillin (1000 mcg/ml), it was very sensitive to streptomycin beyond a concentration of 0.02 mcg/ml. Two stable mutants, one resistant to 1000 mcg penicillin/ml and another to 0.02 mcg streptomycin/ml were isolated, of which the latter had lost its nitrogen fixing capacity. Drug resistance seems to be due to nuclear or gene mutation.

Ethylmethanesulfonate was used as a mutagen to induce auxotrophic mutants in Rhizobium meliloti L5-30. Survival of the culture depended on the period of time during which it was treated with the mutagen. Thirteen auxotrophic mutants were isolated as a result of screening 1404 clones, and their requirements in growtn factors were determined. Ethylmethanesulfonate induced mainly those mutants which required sulfur-containing amino acids. The activity of nitrogen fixation of the auxotrophic mutants was assayed by measuring the reduction of acetylene and the yield of lucerne. Mutants requiring methionine or cystein, cysteine or histidine, and adenine with thiamine were not effective whereas those requiring arginine, tryptophan, and thiamine were capable of nitrogen fixation. Among two methionine auxotrophs, one displayed the activity of nitrogen fixation and the other did not.