Carotenoids of Rhizobia

Abstract

With increasing concentrations in the growth medium of the cyclization inhibitors nicotine or 2-(4-chlorophenylthio)-triethylamine hydrochloride (CPTA) the previously identified bicyclic carotenoids of Rhizobium lupini (2,3,2′,3′-tetrahydroxy-β,β-caroten-4-one and 2,3,2′,3′-tetrahydroxy-β,β-carotene) were successively replaced by hitherto unknown monocyclic carotenoids. By application of mass and nuclear magnetic resonance spectroscopy 3 carotenoids were identified as 2,3-trans-dihydroxy-β,ψ-caroten-4-one, 2,3-trans-dihydroxy-β,ψ-carotene, and 3-hydroxy-β,ψ-caroten-4-one. A further compound was tentatively established as (2- or 3-)monohydroxy-β,ψ-carotene. It was found that other inhibitors such as diphenylamine or 4-chloro-5-(dimethylamino)-2-α,α,α(trifluoro-m-tolyl)-3-(2H)-pyridazinone (San 6706) did not affect the pigment pattern. The results are discussed in relation to carotenoid biosynthesis in Rhizobium lupini.