Nicotine inhibition of lycopene cyclase enhances accumulation of carotenoid intermediates by<i>Dunaliella salina</i>CCAP 19/18

Abstract

The effect of nicotine on the regulation of carotenoid production by Dunaliella salina was investigated. Accumulation by the microalga of lycopene, all-trans and 9-cis β-carotene was assessed in artificial sea water containing different concentrations of nicotine. Nicotine inhibits lycopene cyclase, and consequently the cyclization reactions in the carotenoid pathway. Nicotine concentrations greater than 50 µM suppressed microalgal growth, while concentrations of 100 µM more completely inhibited growth. However, at low concentration nicotine treatment significantly decreased β-carotene, but triggered accumulation of lycopene and other carotenoid intermediates, possibly due to inhibition of β-cyclase and also ε-cyclase. HPLC analysis of the culture medium lacking nicotine showed that isomers of β-carotenes were the major carotenoids of approximately equal portions of all-trans and 9-cis (52 and 48% respectively) while supplementation of the medium with nicotine led to the appearance of lycopene and additional carotenoids, which are supposed to be δ-carotene and γ-carotene.