Phytoene and phytofluene overproduction by Dunaliella salina using the mitosis inhibitor chlorpropham

The halotolerant chlorophyte microalga, Dunaliella salina, is one of the richest sources of carotenoids and will accumulate up to 10% of the dry biomass as beta-carotene, depending on the integrated amount of light to which the alga is exposed during a division cycle. Red light also stimulates beta-carotene production, as well as increases the 9-cis beta-carotene/all-trans beta-carotene ratio. In this paper we investigated the effects of chlorpropham (Iso-propyl-N (3-chlorophenyl) carbamate, CIPC), with and without red light, on carotenoid accumulation. Chlorpropham is a well-known carbamate herbicide and plant growth regulator that inhibits mitosis and cell division. Chlorpropham arrested cell division and induced the massive accumulation of colourless phytoene and phytofluene carotenoids, and, to a much lesser extent, the coloured carotenoids. The chlorophyll content also increased. When phytoene per cell accumulated to approximately the same level with chlorpropham as with norflurazon, a phytoene desaturase inhibitor, coloured carotenoids and chlorophyll increased with chlorpropham but decreased with norflurazon. Cultivation with chlorpropham under red LED light for 2 days did not affect the content of beta-carotene, but phytoene was 2.4-fold the amount that was obtained in cultures under white LED light and the 9-cis beta-carotene/all-trans beta-carotene ratio increased from 1.3 to 1.8. With norflurazon, red LED light boosted the contents of both phytoene and beta-carotene, 2-fold and 1.3-fold respectively compared to those under white LED light, and the ratio of 9-cis beta-carotene/all-trans beta-carotene reached 3.8. The results are discussed in terms of disruption by chlorpropham of synchronised control between nuclear and chloroplast events associated with carotenoid biosynthesis. Since phytoene and phytofluene are colourless carotenoids which are sought after for the development of nutricosmetics and other health/beauty products, the results also present as a new method with low toxicity for production of colourless carotenoids based on the cultivation of D. salina.