Biomedical subjects
Publications and source records attributed to S E Stevens.
The growth response of the marine blue-green alga, Agmenellum quadruplicatum to 60 inorganic and organic nitrogen sources was studied. These compounds were offered as sole nitrogen sources. Most amino acids, most purines, and urea were good nitrogen sources for growth.
A uracil-requiring auxotroph of Anacystis nidulans was isolated after treatment with N-methyl-N'-nitrosoguanidine. Neither precursors in the de novo pyrimidine pathway nor compounds of "salvage" or degradative pathways could replace the uracil requirement. The reversion frequency for mutation to a nonuracil requirement for growth was 2.0 times 10(-8). The calculated average rate of uracil utilization was 1.1 times 10(-17) mol of uracil per unit cell mass/h. The amount of uracil required for the synthesis of a unit cell mass was 3.8 times 10(-17) mol of uracil.
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Characteristics of nitrate reduction in terms of nitrite production in an N-methyl-N'-nitro-N-nitrosoguanidine-induced mutant of the blue-green alga Agmenellum quadruplicatum are described. Following induction of nitrate reduction a linear rate of nitrite production proportional to cell concentration was observed. Rate of nitrite production and growth rate showed similar responses to pH, temperature, and light intensity. If required, only trace amounts of carbon dioxide were necessary for nitrite production. Atmospheres of oxygen or nitrogen inhibited production of nitrite. In addition, a low but constant rate of nitrite production was observed in the dark. Nitrite production by mutant AQ-6 was studied in terms of photosynthesis. As nitrite production proceeded, rate of photosynthesis declined. Ultraviolet irradiation and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea poisoning did not prevent nitrite production. The action spectrum of nitrite production was chlorophyll a-like.
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Results of studies on a larvicidal cyanobacterium that expresses a Bti cryIVD gene fusion are reported. Genetically altered Agmenellum quadruplicatum PR-6 is shown to be toxic to larvae of three major genera of disease-bearing mosquitos. Factors affecting expression of Bti genes in cyanobacteria are discussed.