Ca requirement for aerobic nitrogen fixation by heterocystous blue-green algae

The requirement of Ca²⁺ for growth and nitrogen fixation has been investigated in two strains of heterocystous blue-green algae (Anabaena sp. and Anabaena ATCC 33047). With combined nitrogen (nitrate or ammonium) or with N₂ under microaerobic conditions, Ca²⁺ was not required for growth, at least in concentrations greater than traces. In contrast, Ca²⁺ was required as a macronutrient for growth and nitrogen fixation with air as the nitrogen source. Addition of Ca²⁺ to an aerobic culture without Ca²⁺ promoted, after a lag of several hours, development of nitrogenase activity and cell growth. Provision of air to a microaerobic culture in the absence of Ca²⁺ promoted a drastic drop in nitrogenase activity, which rapidly recovered its initial level upon restoration of microaerobic conditions. Development of nitrogenase activity in response to either Ca²⁺ or low oxygen tension was dependent on de novo protein synthesis. The role of Ca²⁺ seems to be related to protection of nitrogenase from inactivation, by conferring heterocysts resistance to oxygen.     

Physiological and biochemical studies on nitrogen fixation by blue-green algae

Summary The influence of some physiological and environmental conditions on the growth and nitrogen fixation by a local strain of Nostoc commune revealed that the variation of hydrogen ion concentration of the nutritive medium, light intensity and temperature greatly affected the growth rate, cellular nitrogen and extracellular nitrogen of the experimental organism. It was possible however, to formulate the optimum conditions for growth and nitrogen fixation by this organism.     

Pesticide (hexachlorocyclohexane) inhibition of growth and nitrogen fixation in blue-green algae Anabaenopsis raciborskii and Anabaena aphanizomenoides.

The effects of the pesticide hexachlorocyclohexane (HCH) on the nitrogen fixing blue-green algae Anabaenopsis raciborskii and Anabaena aphanizomenoides commonly found as blooms in fish ponds were studied. These algae were very sensitive to HCH, and a distinct decrease in growth rate was observed on prolonged incubation. Lower concentrations (10 microgram/ml) were algistatic and higher concentrations (60 microgram/ml) were algicidal. The inhibition of nitrogen fixation indicated that the presence of HCH might affect overall nitrogen economy of inland waters.     

Nitrogen fixation by unicellular blue-green algae

Summary The ability of some unicellular blue-green algae to grow at the expense of N₂ under aerobic conditions has been confirmed and the distribution of this property in the Chroococcaceae has been investigated. It appears to be confined to strains with spherical cells enclosed by the multilaminate sheaths characteristic of the genus Gloeocapsa. Only two unicellular blue-green algae of this type are now available in pure culture; and their properties are so similar that they may well be independent isolates of the same species.No differences in structure between cells grown with nitrate and N₂ could be detected, either by light or by electron microscopy; under both conditions of growth, the population consists entirely of vegetative cells. These two Gloeocapsa strains can therefore maintain a functional nitrogenase system in vegetative cells that are freely exposed to air.     

The relation of heterocysts and hormogonia to nitrogen fixation and reproduction in blue-green algae

Indications are presented that the heterocysts of a member of theRivulariaceae germinate in NO₃ free medium containing low concentrations of NH₄Cl and glucose. Growth occurred regularly in the absence of combined nitrogen sources (NH₄, NO₃), suggesting N₂ fixation. Phosphate regulates hormogonia release, perhaps indirectly via an influence on differentiation of heterocysts.     

Conversion of acetylene reduction rates to nitrogen fixation rates in natural populations of blue-green algae

Twelve experiments are reported on naturally occurring groups of N₂-fixing blue-green algae in which reduction of acetylene and ¹⁵N₂ were determined simultaneously. Simple averaging of the $\text{C}{}_2\text{H}{}_2\text{N}{}_2$ reduction rates yielded a conversion factor of 4.4. Linear and log transform regression analyses yielded values of 4.8 and 4.2, respectively. Reports estimating nitrogen inputs based on acetylene reduction determinations are evaluated.     

Physiological and biochemical studies on nitrogen fixing blue-green algae

Summary The nature of the nitrogenous products formed in the cells and culture solutions of a nitrogen fixing strain of Nostoc commune was investigated. This organism was able to fix 5.4 mg nitrogen/100 mg dry algal cells. 13% of this cellular nitrogen was present in the soluble form. The assay of the different fractions of this soluble nitrogen was also made. Aspartic acid, glutamic acid and alanine were the only amino acids present in the free form. The extracellular nitrogen amounted to 30% of the total fixed nitrogen. The different fractions of this nitrogen were also assayed. Glutamic acid and aspartic acid were the only free amino acids in the culture solution. The importance of these two acids in the pathway of the fixation mechanism was discussed.     

Physiological and biochemical studies on nitrogen fixing blue-green algae

Summary Experiments were made to investigate the influence exerted by calcium, strontium, cobalt and molybdenum on the growth and nitrogen fixation of a local strain of Nostoc commune.Calcium, cobalt and molybdenum at least in micro amounts were found to be required for the achievement of best growth and highest nitrogen fixation.Calcium seems to be irreplaceable by strontium, the latter element exerted a strong inhibitory action on both growth and nitrogen fixation processes.     

Mesosomes in blue-green algae

Summary Mesosome-like, unit-membrane structures are clearly defined in the blue-green algae, Spirulina and three strains of Synechococcus, after osmium or potassium permanganate fixation and observation with the electron microscope. The membranous structures are distinct from the photosynthetic membranes and, in the case of Spirulina, are frequently observed in cells and can occur in large volume within the cell.     

Growth and nitrogen fixation of unicellular blue-green algaaphanothece castagnei

The alga occurring in rice fields grew in nitrogen-free medium and fixed Ca. 1.5 rng nitrogen per 50 ml of culture in 30 to 35 d of incubation period.     

Factors influencing dark nitrogen fixation in a blue-green alga.

Nitrogen-fixing activity declines first rapidly and then more gradually when Anabaenopsis circularis is transferred from light into dark conditions. The rate and duration of dark acetylene reduction (nitrogen fixation) depend upon conditions prevailing during the preceding light period. Factors (such as light intensity, CO2 concentration, and supply of glucose), which in the light affect photosynthesis and the accumulation of reserve carbon, have a profound effect on dark nitrogen fixation. Glucose greatly promotes nitrogen fixation in the light and supports prolonged nitrogenase activity in the dark. The results suggest that heterotrophic nitrogen fixation by blue-green algae in the field may be important both under light and dark conditions.