197 Microalgae as a source of high-value bioactive compounds Mohammed Hussen Bule 1 , Ishtiaq Ahmed 2 , Faheem Maqbool 3 , Muhammad Bilal 4 , Hafz M. N. Iqbal 5 1 Department of Pharmacy, College of Medicine and Health Sciences, Ambo University, Ambo, Ethi- opia, 2 School of Medical Science, Gold coast campus, Griffth University, Southport QLD 4222, Australia, 3 School of Pharmacy, Pharmacy Australia Centre of Excellence, University of Queensland, Brisbane, QLD 4102, Australia, 4 State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China, 5 Tecnologico de Monterrey, School of Engineering and Sciences, Campus Monterrey, Ave. Eugenio Garza Sada 2501, Monterrey, N.L., CP 64849, Mexico TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Microalgae as an inexhaustible source of bioactive compounds 4. Secondary metabolites from microalgae 4.1. Carotenoids 4.1.1. β-carotene 4.1.2. Astaxanthin 4.1.3. Zeaxanthin and Lutein 4.1.4. Violaxanthin 4.1.5. Fucoxanthin 4.2. Polyunsaturated fatty acids 4.3. Proteins and polypeptide 5. Biological activity of compounds from microalgae 5.1. Antimicrobial 5.2. Antiprotozoal agents 5.3. Anti-infammatory activity 5.4. Antioxidant 5.5. Anticancer activity 6. Conclusion 7. Acknowledgement 8. References [Frontiers In Bioscience, Scholar, 10, 197-216, January 1, 2018] 1. ABSTRACT Microalgae are one of the oldest microorganisms, that grow in various hostile environments, ranging from deserts to Antarctica. The microalgae sustain life in such harsh environments through generation of secondary metabolites. Microalgae biosynthesize a large number of diverse bioactive metabolites with activities on cancer, neurodegenerative diseases, and infectious diseases. Here, we highlight the bioactive compounds that are isolated from microalgae for the purpose of using them as food, and as chemicals in pharmaceutical industry as new agents with therapeutic benefts. 2. INTRODUCTION Most algae are autotrophs that live in freshwater and marine environments. They vary from small unicellular microalgae, such as cyanobacteria and diatoms, to large multicellular macroalgae, such as giant kelp (1). Various types of algae have potent capabilities e.g. high levels of EPS secretion potential that help them to survive under different conditions (2). Organisms lacking external defense mechanisms have developed chemical defense strategies, particularly through the production of secondary metabolites with antibiotic or repellent effects (3). Hence, by cultivating them in an adverse environment particularly upon