Ectothiorhodospira mobilis Pelsh, a photosynthetic sulfur bacterium depositing sulfur outside the cells

Abstract

From salt flats on the Galapagos Islands, two strains of a red photosynthetic bacterium were isolated and identified as Ectothiorhodospira mobilis, an organism first described by Pelsh in 1937. The cells are curved in a short spiral, 0.7 to 1.0 mu wide and 2.0 to 4.8 mu long. They are motile by a polar tuft of flagella. Cells contain several large stacks of lamellar membranes, carrying the pigments bacteriochlorophyll a and carotenoids of the spirillo xanthin series. Cell division occurs by binary fission, not budding. The organism is strictly anaerobic and obligately photosynthetic. Its ability to grow well with sulfide, sulfur, thiosulfate, or sulfite as photosynthetic H donors puts it taxonomically in the Thiorhodaceae. During growth with sulfide, elementary sulfur is deposited outside the cells in the medium and disappears during further growth. A limited number of organic carbon compounds can be utilized as hydrogen donors in place of inorganic sulfur compounds. Under these conditions, sulfate can serve as the sulfur source. The enzymes catalase and hydrogenase are present. The newly isolated strains require vitamin B(12). They also require a salinity of 2 to 3% NaCl, but they are not extreme halophiles. The organism is not identical with any of the species listed in Bergey's Manual.