Extrusion of secondary carotenoid containing vesicles from flagellates of Haematococcus pluvialis (Volvocales; Chlorophyceae)

The unicellular green algae Haematococcus pluvialis (Volvocales; Chlorophyceae) is known as one of the most promising organisms for biotechnological production of ketocarotenoids. Mainly due to their antioxidative properties and their use in fish aquaculture, these compounds are needed in increasing amounts. H. pluvialis accumulates astaxanthin and its esters as secondary carotenoids outside the chloroplast. Recently, we established a cultivation scheme for accumulation of secondary carotenoids in the flagellate state of the microalga. This enabled us to study the accumulation process independent of the processes involved in resting cell (aplanospore; hypnoblast) formation. Here we report on light and electron microscopic investigations of the transport of carotenoids from the chloroplast, the presumed site of carotenoid synthesis. During massive accumulation of secondary carotenoids we did not see any vesicle extrusion from the chloroplast into the cytoplasm but observed transport of carotenoid containing vesicles across the plasmalemma. The latter process might open new strategies to overcome the existing technological problems of ketocarotenoid isolation from resistant thick-walled aplanospores in Haematococcus biotechnology.