A brown species was isolated from a soil sample collected in Java, Indonesia. It has three physiological types of light-absorbing compounds: the photosynthetic pigments (chlorophyll , carotenoids, phycocyanin, phycoerythrin and allophycocyanin), a brown pigment(s) and three UV-absorbing compounds. The organism undergoes complementary chromatic adaptation by varying its phycobilin content. It is resistant to photobleaching at high intensities of white light, and also to UV-C radiation, under which conditions a green-coloured species (ATCC 27895) was killed. Synthesis of the brown pigment and UV-absorbing compounds was not observed at low oxygen levels. A brown pigment was released suddenly from cells during exponential growth, resulting in a deep brown-coloured medium. In addition, the absorption spectrum of the medium after pigment release had maxima in the UV region, at 256 nm, 314 nm and 400 nm. The appearance of the UV-absorbing compounds coincided with the brown pigment release and with the disappearance from the vegetative cells of peripheral granules. The species reduced acetylene, a measure of nitrogen fixation, in both the light and the dark periods when grown on a 12/12 h light/dark cycle. On a 4/20 h light/dark cycle fixation occurred predominantly in the light period. When grown on this restricted light regime, or at very low light intensity, the cells did not produce the brown pigment or the UV-absorbing compounds.


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