Physiology and xanthophyll cycle activity of Nannochloropsis gaditana

The physiology of the violaxanthin-producing microalga Nannochloropsis gadi tana is examined and the effect of environmental factors on the growth and cellular pigment content investigated in batch and continuous cultures. N. gaditana is slow-growing, with a maximum specific growth rate of 0.56 day(- 1) at 23 degreesC. The xanthophyll cycle is present in this strain, but has a much lower activity than in higher plants and other species of Nannochlo ropsis. At 30 degreesC, under high light (1500 mu mol photons m(-2) s(-1)), 33% of the violaxanthin pool was deepoxidated to antheraxanthin (76%) and zeaxanthin (24%) over 60 min. Addition of iodoacetamide dramatically affect ed the xanthophyll cycle activity: 50% of the violaxanthin was replaced by zeaxanthin (90%) within 30 min. This was attributed to an increase in membr ane fluidity following iodoacetamide addition, resulting in a larger pool o f violaxanthin available for conversion. Batch culture studies showed that a decrease in irradiance (from 880 to 70 mu mol photons m(-2) s(-1)) can in crease chlorophyll a and violaxanthin content by as much as 80% and 60%, re spectively. Continuous cultures indicated that violaxanthin is a growth-rat e-dependent product, but the violaxanthin content is less affected by dilut ion rate (in the range 0.12 to 0.72 day(-1)) and pH (6.8 to 7.8) than chlor ophyll a. The optimum conditions for growth and violaxanthin production in continuous culture were found to occur at a dilution rate of 0.48 day(-1), a temperature of between 24 degreesC and 26 degreesC, and pH in the range 7 .1 to 7.3. (C) 2001 John Wiley & Sons, Inc.