Inherent and growth stage-related differences in growth and lipid and sterol composition of algal species sensitive and tolerant to sterol-inhibiting fungicides.

Fourteen algal species representing five algal classes were evaluated as to the effects of four sterol-inhibiting fungicides (SIFs) on growth. Sensitivity to SIFs was related to species, chemical, and concentration. Species of Chlorella sensitive and tolerant to SIFs were further compared relative to inherent and growth stage-related differences in lipid, free sterol (FS), and steryl ester (SE) composition. Inherent and growth stage-related qualitative and quantitative differences in FS and SE composition were apparent between the two species examined. The qualitative FS and SE composition was particularly different. The importance of lipids, FS, and SE in membrane structure and control of membrane function is well established. Species differences and environmentally (growth stage, light, temperature, and nutrition) induced changes in lipid composition may be part of the basis for sensitive and tolerant responses to SIFs and xenobiotics in general. The ability of lipophilic xenobiotics to partition into membranes most likely depends on the qualitative and quantitative composition of membrane components, at any given time, and seems to be highly dynamic. Although the biochemical mechanism of action of SIFs is well established, the ability for passive bioaccumulation of such compounds in algae may be equally as important.