NMR and Ultrafast Spectroscopic and Mass Spectrometry Characterisation of a Carotenoid Isolated from Methylorubrum extorquens strains PA1 and AM1

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Methylorubrum species are prominent members of the plant phyllosphere, where they are exposed to fluctuating environmental conditions, including intense ultraviolet (UV) radiation. To mitigate such stressors, these bacteria commonly synthesise carotenoids as an oxidative protection. In this study, we investigated the carotenoid production of two closely related methylotrophic strai ns, Methylorubrum extorquens PA1 and AM1 (short PA1 & AM1), with a particular focus on the influence of iron availability. We identified and comprehensively structurally characterised the main carotenoid produced by both strains by using ultraviolet–visible (UV– Vis ) spectroscopy, high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS) with collision-induced dissociation (CID), ion mobility–mass spectrometry (IM–MS), nuclear magnetic resonance (NMR) spectroscopy, and ultrafast transient absorption (TA) spectroscopy. We show that both strains produce, unaffected by the iron availability, the same carotenoid, identified as 4-[2-O-11Z-octadecenoyl-β-D-glucopyranosyl]-4,4′-diapo-Ψ,Ψ-carotene-4,4′-dioate. However, the iron availability strongly influenced the carotenoid production making it a tuneable parameter for boosting bacterial carotenogenis in biotechnological settings.

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