Temperature and salinity tolerances of geographically separated Phaeodactylum tricornutum Bohlin strains: maximum quantum yield of primary photochemistry, pigmentation, proline content and growth

To determine eco-physiological responses of three geographically separate strains of Phaeodactylum tricornutum, we exposed cultures of each strain to a combination of temperatures ranging from 12 degrees C to 30 degrees C and salinities from 5 to 130. Generally, the three strains were eurythermal and very euryhaline, especially when measured as maximum quantum yield of primary photochemistry. However, a decline in pigmentation under both hypo-and hyper-saline conditions tracked diminishing growth-rates. Under hyper-saline conditions, growth rates were further reduced as more proline was accumulated in each cell. In salinities >90 at 30 degrees C, the physiological response was reduced to mere cell survival. Regulation of pigmentation and the time-course of both proline accumulation and growth were similar in the two cold-temperate strains from Vancouver and Plymouth, but different in the tropical strain from Guam, mirroring an epigenetic manifestation of environmental influences. In contrast, the tolerance ranges of all three strains seemed to be determined by phylogenetic background. Thus, the cold-temperate strain from Plymouth and the tropical strain from Guam, which are in the same phylogenetic group, had broader salinity and temperature tolerance ranges than the cold-temperate strain from Vancouver, which is in a neighbouring clade.