The harmful alga Aureococcus anophagefferens utilizes 19'-butanoyloxyfucoxanthin as well as xanthophyll cycle carotenoids in acclimating to higher light intensities.

ABSTRACT

Aureococcus anophagefferens is a picoplanktonic microalga that is very well adapted to growth at low nutrient and low light levels, causing devastating blooms ("brown tides") in estuarine waters. To study the factors involved in long-term acclimation to different light intensities, cells were acclimated for a number of generations to growth under low light (20µmolphotonsm(-2)s(-1)), medium light (60 or 90µmolphotonsm(-2)s(-1)) and high light (200µmolphotonsm(-2)s(-1)), and were analyzed for their contents of xanthophyll cycle carotenoids (the D pool), fucoxanthin and its derivatives (the F pool), Chls c(2) and c(3), and fucoxanthin Chl a/c polypeptides (FCPs). Higher growth light intensities resulted in increased steady state levels of both diadinoxanthin and diatoxanthin. However, it also resulted in the conversion of a significant fraction of fucoxanthin to 19'-butanoyloxyfucoxanthin without a change in the total F pool. The increase in 19'-butanoyloxyfucoxanthin was paralleled by a decrease in the effective antenna size, determined from the slope of the change in F(0) as a function of increasing light intensity. Transfer of acclimated cultures to a higher light intensity showed that the conversion of fucoxanthin to its derivative was a relatively slow process (time-frame of hours). We suggest the replacement of fucoxanthin with the bulkier 19'-butanoyloxyfucoxanthin results in a decrease in the light-harvesting efficiency of the FCP antenna and is part of the long-term acclimative response to growth at higher light intensities.