The carotenoids of Myxococcus fulvus (Myxobacterales)

Abstract

1. The carotenoids of Myxococcus fulvus strain Mx f2 were analyzed. The carotenoid content of cultures growing logarithmically in the dark was found to be about 0.003% of the dry weight of acetone extracted cells. This value rose to 0.03% in logarithmically growing cultures in light, and to 0.06% in illuminated late log-phase cultures grown in a fermenter. 2. The organism synthesizes about 50 to 60 different carotenoids, 24 of which could be isolated in sufficient quantities to be identified. 3. The identified pigments were: phytoene (1), phytofluene (2), ζ-carotene (3), neurosporene (4), γ-carotene (5), lycopene (6), torulene (7), 3,4-dehydro-lycopene (8) — 4-keto-γ-carotene (9), 4-keto-torulene (10) — 1′,2′-dihydro-1′-hydroxy-γ-carotene (11), 1,2-dihydro-1-OH-lycopene (12), 1′,2′-dihydro-1′-OH-torulene (13), 3-(or 4-)-OH-torulene (14), 1,2-dihydro-3,4-dehydro-1-OH-lycopene (15) — 4,4′-diketo-γ-carotene (16), 4,4′-diketo-lycopene (17), 1′,2′-dihydro-4,2′-diketo-torulene (18) — 1′,2′-dihydro-1′-OH-4-keto-γ-carotene (19) — a 2′-fatty acid ester of 1′,2′-dihydro-1′,2′-dihydroxy-4-keto-torulene (22) — and the fatty acid esters of the two glucosides myxobacton (23), and myxobactin (24). The hydroxyl groups of two pigments could not be located: 1′,2′-dihydro-trihydroxy-4-keto-torulene (21), and a tetrahydroxy carotenoid with a spheroidene-like chromophore and a nonconjugated ring (20). 4. 2′-Acyl-1′,2′-dihydro-1′,2′-dihydroxy-4-keto-torulene (22) appears to be the first true carotenoid fatty acid ester found in a bacterium. The fatty acid part of the ester was variable and consisted mainly of C16:0, C16:1, C18:0, C18:1, and tentatively identified C21:0. 5. Most of the carotenoids of M. fulvus occur only in trace amounts. The bulk of the pigments is composed of 3 compounds: the two acyl glucosides and 4-ketotorulene.