Search

Curves showing the rate of photosynthesis as a function of light intensity are presented for Chlorella vulgaris growing at a constant light intensity of either 3 or 30 Klux. The rate is given a) per number of cells, b) per unit of weight of chlorophyll (a + b), and c) per unit of wet volume or unit of weight of dry matter. At an illumination of about 3 Klux the average cell size is at its maximum. At the same time the content of chlorophyll per cell is maximal and the content of enzymes active in photosynthesis is very nearly maximal. If we increase the illumination the cell size decreases. At the same time the content of active enzymes per cell increases slightly, but the content of chlorophyll per cell decreases. If we decrease the illumination (from 3 Klux) cells are produced with the maximum content of chlorophyll but decreasing content of enzymes active In photosynthesis. At the same time the cell size decreases. Growth rates at the two light intensities are computed by means of the measured rates of photosynthesis and respiration. They are identical with the growth rates measured by means of the increase in number of cells. After a shift from 3 Klux to 30 Klux it takes only 24 hours before the ratio chlorophyll a+b: dry weight has changed to that normally found at the high light intensity. The same is true concerning the cell size. When shifting from 30 Klux to 3 Klux it takes a little longer. However, a chlorophyll concentration nearly as high as that ordinarily found at 3 Klux was measured. About 36 hours after the shift from 30 Klux to 3 Klux, or vice versa, the shape of the curve giving the rate of photosynthesis as a function of light intensity approaches that characteristic of algae grown constantly at the new light intensity. If Chlorella grown constantly at 30 Klux are transferred to the dark for 22 hours the shape of the tight photosynthesis curve is only moderately changed. IK decreases from 13 to 9 Klux. If instead the algae are transferred to 3 Klux, IK is decreased to 5 Klux after 22 hours. The importance is stressed of using such dilute concentrations of algae in experiments of both growth and photosynthesis that no self shading takes place. [ABSTRACT FROM AUTHOR]

Paper chromatograms of ether and ethanol extracts of cells of the three algal species: Chlorella vulgaris, Scenedesmus quaddricauda and Chlamydomonas reinhardi were tested on agar plates with the bacteria Bacillus subtilis. Inhibition zones were found at the starting line of the paper chromatograms as well as at the solvent front. The inhibition zone at the starting line only occurred after illumination and was due to a light-induced transformation of chlorophyllides. The inhibition zones at the solvent front were caused by two different kinds of substances. The first substance was, like chlorophyllides, a derivative of chlorophylls and only showed inhibiting action after illumination. The second substance had no relation to plant pigments. In extracts from Chlamydomonas it acted only after illumination, but in extracts from Chlorella and Scenedesmus it produced inhibition zones both in the light and the dark. By extraction of culture solutions from the three algal species chlorophyllides were found in the extracts which produced substances inhibiting the growth of Bacillus subtilis both in dark and light. It is suggested that chlorophyllides play a part as an antibacterial substance in natural waters. [ABSTRACT FROM AUTHOR]

Filtered culture solutions from cultures of different unicellular algae, especially Chlorella vulgaris, were tested for content of growth affecting substances using the bacteria Staphylococcus aureus as test organism. Either a decrease or an increase of the growth of the bacteria could be found. It was observed that both growth accelerating and growth inhibiting substances were present simultaneously in the culture solution and that the concentration of the substances varies a great deal in cultures of the same algal species even if the cultures were grown under apparently identical conditions. In one of the experiments the inhibiting effect was decreased by heating the algal filtrate at 70°C for 20 min. In another experiment at least two inhibitors were found. One was inactivated by illumination of the algal filtrate, a second was absorbed to Norit. [ABSTRACT FROM AUTHOR]

Experiments were carried out with algae in mixed cultures (two species cultures) or with algae cultured in filtrates from cultures of other algae or the same species. In experiments with Asterionella formosa and Nitzschia palea it was shown that both species formed substances which inhibited the growth of the other species and that the rate of inhibition was very dependant on the experimental circumstances. It was shown further that Nitzschia formed autotoxic substances and it was suggested that Asterionella formed substances which accelerated the growth of other Asterionella cells and of Nitzschia in some cases. In experiments where Nitzschia was cultured in filtrates from Scenedesmus quadricauda and Chlorella pyrenoidosa cultures, it was shown that Scenedesmus formed substances which considerably inhibited the growth of Nitzschia. The growth of Nitzschia was not inhibited in filtrates from a 4-8 days old Chlorella culture but was distinctly so in filtrates from a 13-17 days old Chlorella culture. When Chlorella was cultured for 3 days in filtrates from a 21 days old Scenedesmus culture a marked inhibition of the growth was found. During 3 days of culturing of Chlorella in filtrate from a 21 days old Nitzschia culture an acceleration of the growth of Chlorella took place. Similarly an inhibition of the growth was found when Scenedesmus was cultured for 3 days in filtrates from a 21 days old Scenedesmus culture. On the other band, an acceleration of the growth of Scenedesmus took place when it was cultured in filtrates from a 21 days old Chlorella and a 21 days old Nitzschia culture, respectively. [ABSTRACT FROM AUTHOR]