PAM fluorometry as a tool to assess microalgal nutrient stress and monitor cellular neutral lipids

This study investigated the use of Pulse Amplitude Modulated (PAM) fluorometry to measure nutrient induced physiological stress and subsequent synthesis of cellular neutral lipids. A freshwater Chlorella sp. was subjected to complete nutrient stress (distilled H2O) and selective nutrient stress in modified BG-11 media (BG-11-N, BG-11-P and BG-11-Fe). Physiological stress was recorded using parameters, rETR, F-v/F-m, E-k, alpha and NPQ. Induced stress became evident when these parameters were significantly altered, suggesting the onset of neutral lipid synthesis. Complete nutrient stress induced the highest yield of cellular neutral lipids (similar to 49%) compared to absence of selected nutrients (similar to 30%). Physiological stress was recorded by a significant decrease in rETR (75%), F-v/F-m (36%), and E-k (60%) and an increase in NPQ (83%). Optimization of neutral lipids occurred by initially maximizing the biomass and subsequently subjecting the harvested biomass to complete nutrient stress. (C) 2010 Elsevier Ltd. All rights reserved.