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Name derivation:
Classification:
Chlorella M.Beijerinck 1890 Order Chlorellales; Family Chlorellaceae; 33 of 96 species descriptions are currently accepted taxonomically (Guiry and Guiry). Synonym: Muriella.
Morphology:
Green spherical to ellipsoidal unicells with one chloroplast, often growing in groups. Asexual reproduction by forming 2- 8 autospores.
Similar genera:
More than 100 taxa (probably species descriptions) have been incorrectly designated Chlorella (Krienitz et al. 2014).
Calvin cycle:
Dark (light-independent) reactions of PS use 9 ATP (fuel) and 6 NADPH (reducing power) molecules to incorporate 3 CO2 molecules into a single precursor of sugars: glyceraldehyde 3-phosphate. Light reactions of PS produce the ATP and NADPH. The cycle was determined with Chlorella cultures (Calvin and Benson 1948).
Biofuel potential:
High lipid content and growth rate are a major considerations for selecting microalgal strains. Of five Chlorella species, C. emersonii growing in culture without a source of nitrogen (none was listed for the ‘low-N’ freshwater growth medium) had ~63% lipid content compared to the control culture grown in Watanbe medium (Watanabe 1960) with 1.25 g KNO3 L^-1. Although the initial growth rate was depressed (days 1-5) it then increased providing the highest yield after one week. The protein content in N-limited culture was decreased (Illman et al. 2000).
Biogas wastewater utilization:
A model of biomethane production using the cyanobactium Spirulina predicted a net energy ratio of 1.54 using an existing biogas plant (Wang et al. 2013), suggesting the value of integrating microalgal production with biogas waste. A test of using industrial wastewater is addition of biogas production wastewater containing 75-80% pure glycerol with methanol, free fatty acids, a catalyst residue and other impurities, added to BG11 medium minus nitrogen that supported mixotrophic growth. Optimal growth was in the growth medium with 0.114 g L^-1 N and 2.7 g L^-1 technical glycerol (Skorupskaite et al. 2015).
Dairy wastewater utilization:
Chlorella sp. developed 23% lipids in ten days when grown on 80% dairy wastewater and 20% BG11 medium (Guruvaiah et al. 2012).
Health food competitor of Spirulina:
Mass culture of Chlorella is also targeting the health food industry with claims of body detoxification, greater longevity and antioxidants (β-carotene).
Habitat:
All aquatic habitats and wet subaerial surfaces.
References:
Beyerinck [Beijerinck], M.W. 1890. Culturversuche mit Zoochlorellen, Lichenengonidien und anderen niederen Algen. Botanische Zeitung 47: 725-739, 741-754, 757-768, 781-785. Calvin, M. and A.A. Benson 1948. The path of carbon in photosynthesis. Science 107:476-480. Guiry, M.D. and Guiry, G.M. 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 18 April 2013. Guruvaiah, M., D. Shah and E. Shah 2014. Biomass and lipid accumulation of microalgae grown on dairy wastewater as a possible feedstock for biodiesel production. International Journal of Science and Research 3(12):909-913. Illman, A.M., A.H. Scragg and S.W. Shales 2000. Increase in Chlorella strains calorific values when grown in low nitrogen medium. Enzyme and Microbial Technology 27:631-635. Krienitz, L., V.A.R. Huss and C. Bock 2014. Chlorella: 125 years of the gre4en survivalist. Trends in Plant Science xx:1-3 (in press). Skorupskaite, V., V. Makareviciend and D. Levisauskas 2015. Optimization of mixotrophic cultivation of microalgae Chlorella sp. for biofuel production using response surface methodology. Algal Research 7:45-50. Watanabe, A. 1960. List of algal strains in the collection at the Institute of Applied Microbiology, University of Tokyo. Journal of General Applied Microbiology 6:283-292. Wang, X., E. Nordlander, E. Thorin and J. Yan 2013. Microalgal biomethane production integrated with an existing biogas plant: A case study in Sweden. Applied Energy 112:468-484.