Microalgae

Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment.^[1] They are unicellular species which exist individually, or in chains or groups. Depending on the species, their sizes can range from a few micrometers (μm) to a few hundred micrometers. Unlike higher plants, microalgae do not have roots, stems, or leaves.^[2] They are specially adapted to an environment dominated by viscous forces.

Microalgae, capable of performing photosynthesis, are important for life on earth; they produce approximately half of the atmospheric oxygen^[3] and use the greenhouse gas carbon dioxide to grow photoautotrophically. "Marine photosynthesis is dominated by microalgae, which together with cyanobacteria, are collectively called phytoplankton."^[4] Microalgae, together with bacteria, form the base of the food web and provide energy for all the trophic levels above them. Microalgae biomass is often measured with chlorophyll a concentrations and can provide a useful index of potential production.^[5][6] Microalgae are very similar to terrestrial plants because they contain chlorophyll, as well as they require sunlight in order to grow and live. They can often be found floating in the top part of the ocean, which is where sunlight touches the water. Microalgae require nitrates, phosphates, and sulfur which they convert into carbohydrates, fats, and proteins. ^[7] Due to this converting ability, they are known to have health and nutritional benefits. It has been found to work as an ingredient in some foods, as well as a biostimulant in agricultural products. ^[8]

The biodiversity of microalgae is enormous and they represent an almost untapped resource. It has been estimated that about 200,000-800,000 species in many different genera exist of which about 50,000 species are described.^[9] Over 15,000 novel compounds originating from algal biomass have been chemically determined.^[10] Examples include carotenoids, fatty acids, enzymes, polymers, peptides, toxins and sterols.^[11] Besides providing these valuable metabolites, microalgae are regarded as a potential feedstock for biofuels and has also emerged as a promising microorganism in bioremediation.^[12] Microalgae is an aquatic organism that has a lot of different bioactive compounds that compose it, including carotenoids, peptides, phenolics, and vitamin B₁₂. Many of them have been found to have positive health effects, which includes anticancer, antihypertensive, anti-obesity, antioxidative, and cardiovascular protection. It has faced lots of challenges due to species diversity and variations in biomass and cultivation factors.^[13]

An exception to the microalgae family is the colorless Prototheca which are devoid of any chlorophyll. These achlorophic algae switch to parasitism and thus cause the disease protothecosis in human and animals.