Phenolic profile of microalgae growing under copper stress

Abstract

Planktonic algae are an important component of natural surface waters. They can regulate the speciation and bioavailability of trace metals through the production and release of organic ligands. These organic ligands bind more than 99% of the total iron and copper in natural waters. Phenolic compounds are natural products involved in responses to different kinds of biotic and abiotic stresses. There is considerable evidence with respect to the implications of phenolic compounds in plants growing in conditions of metal deficiency and stress. Plants accumulate elevated amounts of phenolic compounds for protection and recovery from heavy metal injury. The main chemical process where polyphenols are involved is in the scavenging of Reactive Oxygen Species (ROS). However, few reports have focused on the identification and quantification of polyphenols in microalgae. Determining how polyphenol concentrations change in response to high metal levels will demonstrate the role of these compounds in microalgae and might be useful to help explain the dynamics of this important class of compounds in seawater. The phenolic profile of exudates and extracts of marine microalgae Phaedactylum tricornutum and Dunaliella tertiolecta harvested in natural seawater in the presence and absence of Cu additions was studied, at metal levels of environmental relevance. The experimental findings show changes in the concentrations and types of polyphenols as a function of the metal concentration. The most relevant results show the following: 1) the differences between P. tricornutum and D. tertiolecta owing to their different sensitivities to metal stress; 2) the great increase in phenolic compounds at the highest copper concentration, which may reflect the involvement of these compounds in protection against conditions of copper toxicity; and 3) the phytomedicinal potential of microalgae is underlined by the antioxidant activity of extracts and high contents of phenolic compounds. These microalgae may be exploited for the production of health foods and as an antioxidant carrier in the food and pharmaceutical industries.