Carotenoid Biosynthesis in Micrcoccus luteus Grown in the Presence of Different Concentrations of Nicotine

The results of the present study have shown that in Micrococcus luteus, light was not an absolute requirement for growth and carotenoid biosynthesis, while molecular oxygen was found to be an absolute requirement for both growth and carotenoid biosynthesis. On the other hand, at stationary phase of growth, the yield of the cells grown in the presence of (0 -24 mM ) nicotine was not significantly affected when the cells approached the stationary phase, but concentrations of nicotine in excess of 12 mM caused an initial lag phase which was increased steadily in duration with the increase of nicotine concentration, while no significant differences in the growth –rate amongst treatments within the above range of nicotine concentrations could be seen once the lag-phase was over. It was also found that a complete suppression of the long-chain polar carotenoids was not achieved when the cells grown in the presence of above mentioned concentrations of nicotine. Nicotine did however, resulted in up to 50% inhibition of the long chain polar carotenoids on behalf of the C40 – hydrocarbon carotenoids (carotenes), namely, phytoene, phytofluene, £-carotene and neurosporene. Lycopene however, was an exception. Diphenylamine (DPA) at concentrations of 20 and 25μg / ml culture medium almost completely suppressed the formation of the polar long–chain carotenoids where they found to account to only 1.53 and 0.86 % for total polar epiphasic carotenoids (TPEC) and 0% for the total polar hypophasic carotenoids (TPHC) accompanied by very high increase in C-40 carotenoids level (phytoene in particular). Based on these results it may be suggested that there is a biosynthetic link between the C-40 conventional hydrocarbon carotenoids (carotenes) and the long-chain polar carotenoids (xanthophylls). Lycopene was found not to be on the biosynthetic pathway which leads to the formation the polar long –chain carotenoids.