(6E) and (6Z)-9′-Aporhodoxanthinone, novel carotenoids produced in zeaxanthin-synthesizing-Escherichia coli by redox stress

Abstract

Recombinant Escherichia coli, carrying the crtE, crtB, crtI, crtY, and crtZ genes from the bacterium Pantoea ananatis in addition to the Haematococcus pluvialis idi gene, can dominantly produce zeaxanthin. Vigorous rotary-shaking culture of the recombinant cells to promote strong aeration led to the production of two structurally similar polar carotenoids [1 (3.7%) and 2 (2.9%)] and eschscholtzxanthone (2.3%), along with zeaxanthin (72.6%), β-cryptoxanthin (7.3%), β-carotene (7.1%), and rubixanthin (2.1%). Carotenoids 1 and 2 were purified, and their structures were determined as (6E)-9′-apo-rohodoxanthinone and (6Z)-9′-apo-rhodoxanthinone, respectively, based on UV–vis, MS, 1H NMR, and 13C NMR spectral data. These novel compounds were shown to exhibit excellent singlet oxygen-quenching activity by the methylene blue-sensitized photooxidation system.