Summary report was made on the results of mass culturing of unicellular algae using the method of "open circulation system", which was conducted during the period from 1956 to 1957. Various attempts were made in the device of culture units and the procedure of their operation, and the methods which were found to give satisfactory results were described in detail. Cultures run throughout the year, using certain strains of Chlorella and Scenedesmus gave an average daily yield of 8.6g/m2-day, which corresponds to a yield of 13 metric tons (dry weight) per acre per year.
1. Using Chlorella ellipsoidea as material it was demonstrated that the process of assimilation of nitrate or nitrite was affected by light in quite different ways according as the cells had been placed under dark-adapted or light-adapted condition. The cells cultured with nitrate as the nitrogen source accumulated a large amount of nitrite on long continued illumination, and the nitrite thus accumulated rapidly disappeared when light was turned off (inhibitory effect of light). When the cells were kept in the dark for a sufficient length of time, re-accumulation of nitrite took place. However, this nitrite decreased markedly when the cells (dark-adapted cell) were illuminated (stimulatory effect of light). The rate of formation of amino acids decreased when nitrite was accumulated, and increased when the level of nitrite dropped, indicating that the change of nitrite level was closely related to the amino acid and follow-up protein syntheses. 2. The addition of keto acids to the light-adapted cells decreased the level of nitrite, while practically no effect of the addition was observed with the dark-adapted cells. This observation together with the fact that the amino acids content of light-adapted cells increased markedly when the cells were kept in the dark for a short period of time (30 minutes) led us to the inference that in the light-adapted cells keto acids form the limiting factor for the nitrate assimilation and that the keto acids are accumulated in the dark conceivably owing to the enhanced operation of the Krebs cycle in the darkness. 3. Various experimental results were explained by assuming two factors controlling the process of amino acids synthesis from nitrate. One factor is a photogenic reducing agent(s), R, which is required for the reduction of nitrate and the intermediates between nitrate and amino acids, and the other is keto acids, which react with hydroxylamine or ammonia to form amino acids. The light-adapted cells contain a large amount of R but only a small amount of keto acids, while dark-adapted cells contain a small amount of R but a large amount of keto acids. Along the line of this reasoning, it was postulated that the assimilation of nitrate or nitrite by algal cells would proceed most efficiently when the cells are subject to an intermittent illumination of appropriate intervals.
The growth of a blue green alga, Tolypothrix tenuis was investigated with respect to the effects of various environmental conditions; light intensity, temperature, composition of culture medium. An improved medium for growth experiments and another for economical culture of the alga were devised. The effects of various light intensities on the nitrogen fixation of the organism were investigated. The use of low light intensities for obtaining a good yield of fixed nitrogen was recommended.
It was strongly suggested that a new bacterial species, Kluyvera citrophila nov. sp., which has been reported by Asai et al. as a strain producing a large amount of α-Ketoglutaric acid from glucose, formed this acid via gluconic acid, and perhaps 2-ketogluconic acid, pyruvic acid and the TCA cycle members in the terminal oxidation route, by the following experiments: (1) the Warburg manometric observation on oxygen uptake and carbon dioxide evolution with members of the TCA cycle by intact cells and cell-free extracts, (2) identification of α-Ketoglutaric acid from various substrates such as glucose, gluconic-, 2-ketogluconic-, pyruvic acids and the members of the TCA cycle, by intact cells, (3) detection of C14 incorporation to α-Ketoglutaric acid from C14O2 and glucose or pyruvic acid, and (4) the experiment on the distribution of incorporated C14 in α-Ketoglutaric acid by the degradation method with potassium permanganate.
"Revertant" colonies which occur both spontaneously and by induction with ultraviolet irradiation from auxotrophic mutants of Streptomyces griseo- flavus 142, produced two types of conidia, revertant and parental, in each colony. It is concluded that the most probable explanation is that "revertant" colonies developed from heterozygous conidia. The findings suggest that the conidia of this strain contain a double set of genetic units. Other possibilities are discussed.
1) Using a thermophilic bacterium isolated from compost, new and reliable methods for determining the exact viable count of the organism were developed. By using these methods, systematic studies were made on the viability and growth of the bacterial cells at different temperatures as well as their responses to the change of temperature. 2) It was observed that the organism grew at temperatures between 35°C and 72°C (optimum at 65°C), and died instantly at temperatures above 75°C, and gradually at those below 35°C. In the lower lethal range (10°C- 30°C) bacterial viability was found to be increased by the application of an optimal temperature (65°C) "shock", lasting only for a short period (1.0-1.5 minutes). 3) The importance of these phenomena for comprehension of the mechanism of thermophilic nature of temperature-tolerant organisms was discussed.