Starr, Mortimer P. (University of California, Davis), and William L. Stephens. Pigmentation and taxonomy of the genus Xanthomonas. J. Bacteriol. 87:293-302. 1964.-The colonies formed by phytopathogenic bacteria of the genus Xanthomonas are typically yellow in color. This chromogenesis stems from the presence in all yellow xanthomonads of a particular carotenoid pigment. This unique "Xanthomonas-carotenoid," which has not been found in any yellow nonxanthomonad, is characterized herein to the extent required for its recognition by relatively simple screening procedures. In general, the occurrence of a carotenoid "alcohol" with absorption maxima at 418, 437, and 463 mmu (petroleum ether)-in a gram-negative, polarly-flagellated, oxidative, rod-shaped bacterium-would suggest placement of that microorganism in the genus Xanthomonas.