Study of the catalytic properties of different β-carotene oxygenases (bkt) for their expression in Chlamydomonas reinhardtii

I. Couso and R. León

Biochemistry Lab., Dpto. Química y Ciencia de Materiales. Universidad de Huelva. Avd. Fuerzas Armadas s/n. 21071, Huelva. Spain

Only a limited number of microalgae such as the chlorophytes Haematococcus pluvialis and Chlorella zofigiensis are able to synthesise ketocarotenoids, which are highly demanded as feed supplement for fish aquaculture. The production of ketocarotenoids by these algae is an unusual exception because most microalgae and higher plants do no posses the β-carotene ketolase (bkt) activity. In Chlamydomonas a gene coding a non-functionally protein with high homology to the ketolases of H. pluvialis has been found (Lohr et al., 2005). β-carotene oxygenase (BKT) mediates the addition of keto groups to the position C4 of β-ione-rings of carotenoids, such as β-carotene. Some BKTs have also shown ability to oxygenate hydroxylated carotenes, such as zeaxanthin. We have previously demonstrated that expression of the bkt1 cDNA of Haematococcus (X86782) in C. reinhardtii allows the synthesis of 4-keto-lutein (León et al., 2007). In the present work we have isolated other bkt cDNAs from Haematococcus and Chlorella zofigienses and studied their catalytic efficiency and their ability to oxygenate different substrates by complementation studies in β-carotene and zeaxanthin-accumulating bacteria. The quantity and nature of the ketocarotenoids produced in transgenic Chlamydomonas expressing these genes is now under study. Lohr, M., Chung-Soon, I. and Grossman, A.R. (2005). Plant Physiol. 138, 490-515. León R., Couso I and Férnandez E. (2007). J. Biotechnol. 130(2):

e-mail address of presenting author: inmaculada.couso@dqcm.uhu.es