Regulation of photosynthetic and hemolytic activity of Phaeocystis globosa under different light spectra.

Abstract

Phaeocystis globosa frequently proliferates in eutrophic waters and forms ichthyotoxic algal blooms that cause massive fish mortalities in marine ecosystems. One of the ichthyotoxic metabolites was identified as the glycolipid-like hemolytic toxin, reported to be initiated under light conditions. However, the association between hemolytic activity (HA) and photosynthesis of P. globosa remained unclear. Light spectra (blue, red, green, and white) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) were selected as the stressors to stimulate the hemolytic response of P. globosa in relation to the light and dark photosynthesis reaction. Hemolytic activity in P. globosa was sensitive to the light spectrum as it decreased from 93% to nearly undetectable (1.6%) within 10 min of transfer from red (630 nm) to green light (520 nm). This indicates that the vertical transformation of P. globosa from deep to surface waters (dominated by green light and all light spectra, respectively) may drive the hemolytic response in coastal waters. However, regulation of photosynthetic electron transfer in the light reaction of P. globosa was excluded by the evidence of inconsistent response of HA to photosynthetic activity. The biosynthesis of HA may interfere with the pathway of photopigments diadinoxanthin or fucoxanthin, and the metabolism of three- and five-carbon sugars (GAP and Ru5P, respectively), which ultimately lead to changes in the alga's hemolytic carbohydrate metabolism.