Identification of an anthraquinone pigment and a hydroxystilbene antibiotic from Xenorhabdus luminescens

The entomopathogenic bacterium Xenorhabdus luminescens produces a red pigment and an antibiotic in insect carcasses in which it grows and in axenic cultures. The pigment was purified and identified as the anthraquinone derivative 1,6-dihydroxy-4-methoxy-9,10-anthraquinone, which exhibits a pH-sensitive color change, i.e., it is yellow below pH 9 and red above pH 9. The antibiotic was also purified and identified as the hydroxystilbene derivative 3,5-dihydroxy-4-isopropylstilbene.