Comparison of astaxanthin accumulation and biosynthesis gene expression of three Haematococcus pluvialis strains upon salinity stress

The green alga Haematococcus pluvialis is able to produce and accumulate large amounts of astaxanthin under stress conditions, but not every strain has such a capability. At present, there is little information on how strains differ for astaxanthin production. In this study, three Australian strains of H. pluvialis (New South Wales (NSW), South Australia (SA) and Queensland (QLD)) were cultured and exposed to 0.17 M NaCl for 10 days, to compare their molecular profiles for astaxanthin accumulation and carotenogenesis. After 10 days of salinity stress, the astaxanthin contents of strains NSW, SA and QLD increased up to 16.2, 5.6 and 17.7 mg g(-1) dry weight (DW), respectively. Astaxanthin accumulation was more efficient in H. pluvialis QLD, followed by strain NSW and then SA. The transcript abundance of seven carotenogenesis genes (ipi-1, ipi-2, psy, lyc, crtR-B, bkt2 and crtO) was upregulated with different patterns and incremental expression levels amongst the three strains. The early upregulation of the rate-limiting genes, psy, lyc, bkt2, crtR-B and crtO, was more pronounced in the superior astaxanthin-accumulating QLD and NSW strains. Although the increased transcript level of carotenoid genes was not correlated to the different astaxanthin accumulation between the three strains, expression patterns of these genes likely are strain-specific. Overall, H. pluvialis strains QLD and NSW showed good potential to produce high astaxanthin contents, and the former strain displayed a higher productivity upon salinity stress.