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. They are specially adapted to an environment dominated by viscous forces.

Nannochloropsis microalgae
Collection of microalgae cultures in CSIRO's lab

Microalgae, capable of performing photosynthesis, are important for life on earth; they produce approximately half of the atmospheric oxygen[2] and use the greenhouse gas carbon dioxide to grow photoautotrophically. "Marine photosynthesis is dominated by microalgae, which together with cyanobacteria, are collectively called phytoplankton."[3] 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.[4][5]

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.[6] Over 15,000 novel compounds originating from algal biomass have been chemically determined.[7] Examples include carotenoids, antioxidants, fatty acids, enzymes, polymers, peptides, toxins and sterols.[8] Besides providing these valuable metabolites, microalgae is regarded as a potential feedstock for biofuels and has also emerged as a promising microorganism in bioremediation.[9]

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.

Characteristics and uses
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A variety of unicellular and colonial freshwater microalgae

The chemical composition of microalgae is not an intrinsic constant factor but varies over a wide range of factors, both depending on species and on cultivation conditions. Some microalgae have the capacity to acclimate to changes in environmental conditions by altering their chemical composition in response to environmental variability. A particularly dramatic example is their ability to replace phospholipids with non-phosphorus membrane lipids in phosphorus-depleted environments.[10] It is possible to accumulate the desired products in microalgae to a large extent by changing environmental factors, like temperature, illumination, pH, CO2 supply, salt and nutrients.

Microphytes also produce chemical signals which contribute to prey selection, defense, and avoidance. These chemical signals affect large scale tropic structures such as algal blooms but propagate by simple diffusion and laminar advective flow.[11][12] Microalgae such as microphytes constitute the basic foodstuff for numerous aquaculture species, especially filtering bivalves.

Photo- and chemosynthetic algae

Photosynthetic and chemosynthetic microbes can also form symbiotic relationships with host organisms. They provide them with vitamins and polyunsaturated fatty acids, necessary for the growth of the bivalves which are unable to synthesize it themselves.[13] In addition, because the cells grow in aqueous suspension, they have more efficient access to water, CO2, and other nutrients.

Microalgae play a major role in nutrient cycling and fixing inorganic carbon into organic molecules and expressing oxygen in marine biosphere.

While fish oil has become famous for its omega-3 fatty acid content, fish do not actually produce omega-3s, instead accumulating their omega-3 reserves by consuming microalgae. These omega-3 fatty acids can be obtained in the human diet directly from the microalgae that produce them.

Microalgae can accumulate considerable amounts of proteins depending on species and cultivation conditions. Due to their ability to grow on non-arable land microalgae may provide an alternative protein source for human consumption or animal feed.[14] Microalgae proteins are also investigated as thickening agents[15] or emulsion and foam stabilizers[16] in the food industry to replace animal based proteins.

Some microalgae accumulate chromophores like chlorophyll, carotenoids, or phycobiliproteins that may be extracted and used as coloring agents.[17]

Cultivation of microalgae
Main article: Culture of microalgae in hatcheries

A range of microalgae species are produced in hatcheries and are used in a variety of ways for commercial purposes, including for human nutrition,[18] as biofuel,[19] in the aquaculture of other organisms,[20] in the manufacture of pharmaceuticals and cosmetics,[21] and as biofertiliser.[22] However, the low cell density is a major bottleneck in commercial viability of many microalgae derived products, especially low cost commodities.[23]

Studies have investigated the main factors in the success of a microalgae hatchery system to be:[24][25]

  • Geometry and scale of cultivation systems (referred as photobioreactors);
  • Light intensity;
  • Concentration of carbon dioxide (CO2) in the gas phase
  • Nutrient levels (mainly N, P, K)
  • Mixing of culture

See also

References
  1. Thurman, H. V. (1997). Introductory Oceanography. New Jersey, USA: Prentice Hall College. ISBN 978-0-13-262072-7.
  2. Williams, Robyn (25 October 2013). "Microscopic algae produce half the oxygen we breathe". The Science Show. ABC. Retrieved 11 November 2020.
  3. Parker, Micaela S.; Mock, Thomas; Armbrust, E. Virginia (2008). "Genomic Insights into Marine Microalgae". Annual Review of Genetics. 42: 619–645. doi:10.1146/annurev.genet.42.110807.091417. PMID 18983264.
  4. Thrush, Simon; Hewitt, Judi; Gibbs, Max; Lundquist, Caralyn; Norkko, Alf (2006). "Functional Role of Large Organisms in Intertidal Communities: Community Effects and Ecosystem Function". Ecosystems. 9 (6): 1029–1040. doi:10.1007/s10021-005-0068-8. S2CID 23502276.
  5. Sun, Ning; Skaggs, Richard L.; Wigmosta, Mark S.; Coleman, André M.; Huesemann, Michael H.; Edmundson, Scott J. (July 2020). "Growth modeling to evaluate alternative cultivation strategies to enhance national microalgal biomass production". Algal Research. 49: 101939. doi:10.1016/j.algal.2020.101939. ISSN 2211-9264. S2CID 219431866.
  6. Starckx, Senne (31 October 2012) A place in the sun - Algae is the crop of the future, according to researchers in Geel Flanders Today, Retrieved 8 December 2012
  7. Cardozo, Karina H.-M.; Thais, Guaratini; Marcelo P., Barros; Vanessa R., Falcão; Angela P., Tonon; Norberto P., Lopes; Sara, Campos; Moacir A., Torres; Anderson O., Souza; Pio, Colepicolo; Ernani, Pinto (2006-06-29). "Metabolites from algae with economical impact". Comparative Biochemistry and Physiology C. 146 (1–2): 60–78. doi:10.1016/j.cbpc.2006.05.007. PMID 16901759.
  8. Ratha SK, Prasanna R (February 2012). "Bioprospecting microalgae as potential sources of "Green Energy"—challenges and perspectives". Applied Biochemistry and Microbiology. 48 (2): 109–125. doi:10.1134/S000368381202010X. PMID 22586907. S2CID 18430041.
  9. Yuvraj (2022). "Microalgal Bioremediation: A Clean and Sustainable Approach for Controlling Environmental Pollution". Innovations in Environmental Biotechnology. Vol. 1. Singapore: Springer Singapore. pp. 305–318. doi:10.1007/978-981-16-4445-0_13. ISBN 978-981-16-4445-0.
  10. Bonachela, Juan; Raghib, Michael; Levin, Simon (Feb 21, 2012). "Dynamic model of flexible phytoplankton nutrient uptake". PNAS. 108 (51): 20633–20638. doi:10.1073/pnas.1118012108. PMC 3251133. PMID 22143781.
  11. Wolfe, Gordon (2000). "The chemical Defense Ecology o Marine Unicelular Plankton: Constraints, Mechanisms, and Impacts". The Biological Bulletin. 198 (2): 225–244. CiteSeerX 10.1.1.317.7878. doi:10.2307/1542526. JSTOR 1542526. PMID 10786943.
  12. "growing algae". WUR. Retrieved 2009-05-19.
  13. "ENERGY FROM ALGAE (includes scientific names)". ifremer. Archived from the original on 2006-11-28. Retrieved 2006-09-13.
  14. Becker, E. W. (1 March 2007). "Micro-algae as a source of protein". Biotechnology Advances. 25 (2): 207–210. doi:10.1016/j.biotechadv.2006.11.002. PMID 17196357.
  15. Grossmann, Lutz; Hinrichs, Jörg; Weiss, Jochen (24 September 2020). "Cultivation and downstream processing of microalgae and cyanobacteria to generate protein-based technofunctional food ingredients". Critical Reviews in Food Science and Nutrition. 60 (17): 2961–2989. doi:10.1080/10408398.2019.1672137. PMID 31595777. S2CID 203985553.
  16. Bertsch, Pascal; Böcker, Lukas; Mathys, Alexander; Fischer, Peter (February 2021). "Proteins from microalgae for the stabilization of fluid interfaces, emulsions, and foams". Trends in Food Science & Technology. 108: 326–342. doi:10.1016/j.tifs.2020.12.014.
  17. Hu, Jianjun; Nagarajan, Dillirani; Zhang, Quanguo; Chang, Jo-Shu; Lee, Duu-Jong (January 2018). "Heterotrophic cultivation of microalgae for pigment production: A review". Biotechnology Advances. 36 (1): 54–67. doi:10.1016/j.biotechadv.2017.09.009. PMID 28947090.
  18. Leckie, Evelyn (14 Jan 2021). "Adelaide scientists turn marine microalgae into 'superfoods' to substitute animal proteins". ABC News. Australian Broadcasting Corporation. Retrieved 17 Jan 2021.
  19. Chisti, Yusuf (2008). "Biodiesel from microalgae beats bioethanol" (PDF). Trends in Biotechnology. 26 (3): 126–131. doi:10.1016/j.tibtech.2007.12.002. PMID 18221809.
  20. Arnaud Muller-Feuga (2000). "The role of microalgae in aquaculture: situation and trends" (PDF). Journal of Applied Phycology. 12 (3): 527–534. doi:10.1023/A:1008106304417. S2CID 8495961.
  21. Isuru Wijesekara; Ratih Pangestuti; Se-Kwon Kim (2010). "Biological activities and potential health benefits of sulfated polysaccharides derived from marine algae". Carbohydrate Polymers. 84 (1): 14–21. doi:10.1016/j.carbpol.2010.10.062.
  22. Upasana Mishra; Sunil Pabbi (2004). "Cyanobacteria: a potential biofertilizer for rice" (PDF). Resonance. 9 (6): 6–10. doi:10.1007/BF02839213. S2CID 121561783.
  23. Yuvraj; Ambarish Sharan Vidyarthi; Jeeoot Singh (2016). "Enhancement of Chlorella vulgaris cell density: Shake flask and bench-top photobioreactor studies to identify and control limiting factors". Korean Journal of Chemical Engineering. 33 (8): 2396–2405. doi:10.1007/s11814-016-0087-5. S2CID 99110136.
  24. Yuvraj; Padmini Padmanabhan (2017). "Technical insight on the requirements for CO2-saturated growth of microalgae in photobioreactors". 3 Biotech. 07 (2): 119. doi:10.1007/s13205-017-0778-6. PMC 5451369. PMID 28567633.
  25. Yuvraj; Ambarish Sharan Vidyarthi; Jeeoot Singh (2016). "Enhancement of Chlorella vulgaris cell density: Shake flask and bench-top photobioreactor studies to identify and control limiting factors". Korean Journal of Chemical Engineering. 33 (8): 2396–2405. doi:10.1007/s11814-016-0087-5. S2CID 99110136.
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