Carotenoid pigments of halophilic bacteria

The carotenoids of two yellow and four red halophilic bacteria were studied by chromatography on alumina. One yellow organism contained predominantly one pigment, or a group of closely related pigments similar to neurosporene, while the other contained the neurosporene-like pigments and appreciable amounts of an unknown pigment with absorption maxima at about 420, 450, and 485 mμ.The red organisms, three species of Halobacterium and one Sarcina, contained α- and β-bacterioruberin, and at least six minor pigments. All except two of these were very similar to carotenoids previously reported in Rhodospirillum rubrum. Methoxyl could not be detected in α-bacterioruberin, supporting the suggestion of others that it is demethylated spirilloxanthin. It is suggested that the pathway of carotenoid biosynthesis in red halophiles is very similar to that in Rhodospirillum rubrum, except that the pigments are not methylated.The carotenoid content of Halobacterium salinarium was not influenced by addition of various precursors to the growth medium, or by altering the physical conditions of growth, but increased with the age of the culture.