Haematococcus lacustris is an important species of green algae because it produces
the high-value carotenoid astaxanthin. Astaxanthin production is enhanced by various
stress conditions causing the transformation of green vegetative cells to red cells
with high amounts of astaxanthin, which plays various photoprotective and antioxidant
roles. Although intensive research has been conducted to reveal the regulation of
astaxanthin production, the photosynthetic capacity of the various cell forms is unresolved
at the single-cell level. In this work, we characterized the photosynthetic and morphological
changes of Haematococcus cells, using a combination of microfluidic tools and microscopic
chlorophyll fluorescence imaging. We found marked but reversible changes in the variable
chlorophyll fluorescence signatures upon the transformation of green cells to red
cells, and we propose that the photosynthetic activity as revealed by single-cell
chlorophyll fluorescence kinetics serves as a useful phenotypic marker of the different
cell forms of Haematococcus.
