Abstract

       Life on earth is sustained by the photosynthetic activity of the plants creating a favorable, oxygen rich atmosphere essential for survival of many organisms. Among the many plant species algae are most diverse category ranging from multicellular macroalgae to unicellular microalgae that are explored for many bioactive compounds and commercial applications. For instance, the biological drugs produced by bacteria, fungi or in mammalian tissue culture are expensive and scientists look for different sources for cost reduction. Being abundant, resilient, cheap and easy to culture and also for its ability in folding complex proteins algae come as an alternate source for various products. Moreover, algae not only contribute to the global photosynthetic activity but also form the source of food chain for more than 70% global biomass. This review article presents a brief account on the diversity of algae, its potential by products for commercial applications.

Introduction

         In search of useful products from natural resources, studies have been concentrated mostly on bacteria, fungi and also on higher plants. However, algae comprise of heterogeneous group of organisms ranging from microscopic blue green algae, Cyanobacteria which are closely related to gram negative bacteria to macroscopic algae such as Seaweed which is more similar to the higher plant forms and represent a significant proportion of the world’s biodiversity. Algae are also the group of plants that dominate the aquatic environment (Raymount, 1984). These are essentially the simplest plants, with no vascular system and cells with relatively little differentiation among them. Even the giant seaweeds are aggregation of relatively undifferentiated cells (Cannell, 1993). Algae are widely known for their uses as a food source and also for their secondary metabolites which possess biological activity such as toxicity, antibacterial, antifungal, antiviral, antitumor and other specific activities. An indication of diversity of algae and their biologically active products is discussed in this review.

Algae

         Algae are organisms that require aquatic environments but they can also practically inhabit at all inhabitable environments ranging from deserts to polar snows and also make up most of the world’s biomass. In nature, algae appear in various forms such as single-celled organisms, as colonies of similar or identical cells, as filaments (both branched and unbranched), as membranous thalli, and as complex multicellular structures (as exemplified by the kelps). There are basically two structural groups, the microalgae and the macroalgae. Microalgae are best seen under a microscope; the individual organisms are often less than 1 mm in their largest dimension. Macroalgae, on the other hand, can be seen with the unaided eye. Commonly algae are known to grow in fresh water and seawater. Yet, there are some species which grow in extremely high-salt environments, some inhabit at the subsurface water column and a few that thrive at the limits of the photic zone (which is often 200-300 m below the surface). Algae can also grow in soils (from rich humuses to desert sands), inside rocks, in snow fields, and in more exotic locations, such as the fur of sloths and polar bears. Algae can either be free living or exist in association with other organisms, as in the case of lichens.

         Among the plants, algae are estimated to be the most diverse group and yet only little have been identified (Table 1). Estimates for number of species of algae are about 200 - 350 thousand of which about 40,000 species are described. Algae are found in the three kingdoms Monera, Protista and Plantae comprising many divisions under them. Radmer (1996) summarized some of the major groups of algae based on the description by Lee (1989). Characteristics such as nature of nucleus, pigment, protein and storage products of algae are used for differentiation and this is summarized (Table 2). The affiliations of the various algal groups and their relationship with other taxonomic groups have been described phylogenetically using 16s rRNA Sequences by Wainright et al. (1993) and Hecht (1993) (Radmer, 1996). The phylogenetic classification of the algae is still not standardized and is a subject of frequent revision. The blue green algae comprise of Cyanobacteria are prokaryotes which are commonly related to bacteria and are known to be the progenitors of chloroplast of some higher plants and algae. The green algae are closely related to higher plants while the dinoflagellates and euglenoids have characteristics intermediate to both prokaryotes and eukaryotes, hence placed as mesokayrotes.

Table 1: Estimated numbers of plant species in the world (Prance, 2000).

Algal products

         The macroalgae generally known as seaweeds that include red, brown and green algae are cultured as a source of food. Macroalgae are rich in protein, carbohydrate, amino acids, vitamins and trace elements (Waaland, 1981). The cell walls of brown algae contain alginates that are hydrocolloids used in food and pharmaceutical industries. Microalgae such Chlorella, Astaxhanthin and Spirulina possess anti-cancer, immune stimulatory, detoxifying, anti-diabetic, anti-inflammatory, antihypertensive and digestive properties consumed as food supplement (Lordan et al., 2011). While, caulerpin present in red and green algae is anti-inflammatory; the sulphated polysaccharide present in them act as pro-inflammatory. The fucodans, sulphated polysaccharide from brown algae is also anti-inflammatory. Some algae are used as anticoagulants, antibiotics, antihypertensive agents, blood cholesterol reducers, dilatory agents, insecticides, and anti-tumorigenic agents. In cosmetics, algae act as thickening agents, water-binding agents, and as antioxidants (Kharkwal et al., 2012). Microalgae are huge resources of very long-chain omega-3 and omega-6 polyunsaturated fatty acids (VLC-PUFA) for human nutrition and medicinal applications which has yet to be optimized from this resource (Khozin-Goldberg et al., 2016). The pigments produced by the microalgae such as carotenoids, xanthophyll and phycobillins are used as fluorescent markers in cell biology, colorants in foods, cosmetics and pharmaceutical products.

         Macro and micro algae are well known to be used in waste water treatment plants in sequester, for the removal or transformation of pollutants. In the treatment processes, algal biomass is also produced which is used in the production of chemicals, biofuels or biogas and bioadsorbtion i.e used for removal of toxic heavy metals (Zeraatkar et al., 2016). With increasing demand for fuel, shortly the near future the finite supply of fossil fuels will be exhausted. Therefore, sustainable renewable biofuel is an alternative. Though biofuels can be produced from various sources, the yield is higher from algae compared to any other resource but still it has to be improvised to make algal biofuels economical to compete with fossil fuels. There are many potential applications from algae reported so far. A general schematic for algal biomass fractionation and co-product generation is given in figure 1 (Foley et al., 2011).

Figure1: General schematic for algal biomass fractionation and co-product generation. References are provided in italics (Foley et al., 2011).

Conclusion

         Algae are the most diverse groups with vast genetic and metabolite resources. The algae can be utilized in various sectors of food, health and medicines. The waste water could be effectively treated and toxins could be removed by algae to make it as a sustainable resource. Biofuel production from algae is expensive, yet it is a prospective alternative sustainable fuel resource. Algae are used in many ways and still many applications are yet to be explored on account of its estimated diversity only 15% is identified and if explored further many new possibilities could be discovered from this fascinating organisms.

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