Abstract
BackgroundRecent years have witnessed a rising trend in exploring microalgae for valuable carotenoid products as the demand for lutein and many other carotenoids in global markets has increased significantly. In green microalgae lutein is a major carotenoid protecting cellular components from damage incurred by reactive oxygen species under stress conditions. In this study, we investigated the effects of abiotic stressors on lutein accumulation in a strain of the marine microalga D. salina which had been selected for growth under stress conditions of combined blue and red lights by adaptive laboratory evolution.ResultsNitrate concentration, salinity and light quality were selected as three representative influencing factors and their impact on lutein production in batch cultures of D. salina was evaluated using response surface analysis. D. salina was found to be more tolerant to hyper-osmotic stress than to hypo-osmotic stress which caused serious cell damage and death in a high proportion of cells while hyper-osmotic stress increased the average cell size of D. salina only slightly. Two models were developed to explain how lutein productivity depends on the stress factors and for predicting the optimal conditions for lutein productivity. Among the three stress variables for lutein production, stronger interactions were found between nitrate concentration and salinity than between light quality and the other two. The predicted optimal conditions for lutein production were close to the original conditions used for adaptive evolution of D. salina. This suggests that the conditions imposed during adaptive evolution may have selected for the growth optima arrived at.ConclusionsThis study shows that systematic evaluation of the relationship between abiotic environmental stresses and lutein biosynthesis can help to decipher the key parameters in obtaining high levels of lutein productivity in D. salina. This study may benefit future stress-driven adaptive laboratory evolution experiments and a strategy of applying stress in a step-wise manner can be suggested for a rational design of experiments.
Highlights
Recent years have witnessed a rising trend in exploring microalgae for valuable carotenoid products as the demand for lutein and many other carotenoids in global markets has increased significantly
A fixed photon flux of 170 μE/m2/s was supplied to the PBRs in all the Response surface methodology (RSM) experiments and the center point of the design was chosen as 1.5 M NaCl, 31.2 mM KNO3 and 25% blue light-emitting diode (LED)
These growth conditions were previously applied to D. salina HI 001 for enhancing growth and carotenoid accumulation through adaptive evolution [7]
Summary
Recent years have witnessed a rising trend in exploring microalgae for valuable carotenoid products as the demand for lutein and many other carotenoids in global markets has increased significantly. In adaptation to stress conditions, plants and microalgae show similar patterns of signal transduction, e.g. involving the extracellular signalregulated kinase (ERK) pathway [12] and generating reactive oxygen species (ROS) as secondary messengers and mediators [13] Both enzymatic and nonenzymatic antioxidants play important roles in the defense mechanism against oxidative damage, both by scavenging ROS and by inhibiting their generation. Lutein is a major carotenoid in the light harvesting antenna of green algae and higher plants It plays an important role in harvesting blue light and in transferring energy to the photosystem reaction center, as well as protecting the photosynthetic apparatus against oxidative stress caused by ROS [14]. It is interesting to examine systematically the effects of representative abiotic stressors on the lutein production of D. salina HI 001 in batch culture
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