Euglena

Abstract: I t would appear desirable in photosynthesis studies to work with an organism which exhibits typical green plant photosynthesis, and also possesses the ability to utilize a variety of organic compounds for growth in the dark. The green flagellate, Euglena gracilis, var. bacillaris was commended to us by Dr. S. H. HUT~ER as such an organism. B~glena gracilis has not been used previously in photosynthesis studies, but extensive data on the nutrition of the organism are available (cf. reviews by Lwo~, 1932, 1943; TRAGE•, 1941; HALL, 194i, 1943; DOYLe, 1943; Jaa~, 1946; PRI~CS~IM, 1948; REI~HARD% 1950; HUTNv.R and PROVASOLI, 1951). However, conflicting reports exist on suitable nitrogen sources (PRI~GSH~r~, 1914; DuSI, 1933), on utilizable carbon sources (MAI~x, 1928; DUST, 1933; J~m~, 1935; PRI~rOSHE~, 1937), and on the nature of growth factor requirements for E. gracilis (P~I~OSHEr~, 1914; HuT~.t~, 1936; [ELLIOTT, 1937; LWOFF and DusI, 1938; HALL and SCHOE~BOR~, 1939; SCHOENBORI% 1942). The data from which the discrepancies concerning Euglena nutrition arise were obtained by techniques which do not permit quantitative estimation of growth characteristics, as summarized by Mol~oD (1942, 1949) and MYERS (1951). A major obstacle to earlier work was the lack of a complete medium, only recently defined when HUT~EI% et al. (1949) showed that a combination of vitamin BI~ and thiamin satisfied the growth factor requirements of the organism. In order to obtain background information for studies on the possibility of CO~ replacement in the metabolism of Euglena to be presented in a succeeding paper, a survey of the salient growth and photosynthetic characteristics of the species was undertaken. The results of this work are reported here and include definition of the requirements for maximal growth of Euglena in the light and in darkness ; determination of utilization of carbon sources; and characterization of photosynthesis in this flagellate.

Abstract: Blue light regulates processes such as the development of plants and fungi and the behaviour of microbes. Two types of blue-light receptor flavoprotein have been identified: cryptochromes, which have partial similarity to photolyases, and phototropins, which are photoregulated protein kinases. The former have also been found in animals with evidence of essential roles in circadian rhythms. Euglena gracilis, a unicellular flagellate, abruptly changes its swimming direction after a sudden increase or decrease in incident blue light intensity, that is, step-up or step-down photophobic responses, resulting in photoavoidance or photoaccumulation, respectively. Although these photobehaviours of Euglena have been studied for a century, the photoreceptor molecules mediating them have remained unknown. Here we report the discovery and biochemical characterization of a new type of blue-light receptor flavoprotein, photoactivated adenylyl cyclase, in the photoreceptor organelle of Euglena gracilis, with molecular genetic evidence that it mediates the step-up photophobic response.

Abstract: SUMMARY. An improved assay of vitamin B12 is described. The z strain of Euglena gracilis, which grows more vigorously than the bacillaris strain previously used, is recommended. The pattern of B12 specificity of the two strains appears to be the same. A new medium containing sucrose, aspartic acid, glutamic acid, and glycine at pH 3.6 is well buffered and allows luxuriant growth. Vigorous utilization of sugar appears to depend on readily available nitrogen and a Krebs-cycle component; these requirements are well met by aspartic acid (or asparagine) and glutamic acid. The proposed procedure is especially suitable for the measurement of B12 in blood serum because rise in pH and precipitation of serum proteins during incubation are minimized. Like bacillaris, the z strain allows the distinction between “combined” and “uncombined” B12 in serum. Serum may be an appropriate test material to tell whether such phagotrophs as Peranema can better utilize bound forms of vitamins than can the related osmotrophs. Patterns of B12 requirements and occurrence are discussed as phylogenetic markers.

Abstract: It is proposed that the chloroplasts of Euglena have arisen from the progressive reduction of endosymbiotic green algae. The theory is supported by the presence of a third membrane around the chlor...