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Microalgae II: Cell Structure, Nutrition and Metabolism
Published in Arun Kumar, Jay Shankar Singh, Microalgae in Waste Water Remediation, 2021
Most of the microalgae contain chlorophylls (Chl a, b, c, d) and carotenoids (carotenes and xanthophylls) as their photosynthetic pigments, but cyanobacteria and red algae also have phycobilins (phycoerythrobilin, phycocyanobilin and phycourobilin).Chlorophylls have two absorption ranges: (a) blue or blue-green (450–475 nm) and (b) red (630–675 nm); while carotenoids and phycobilins have an absorption range of 400–550 nm and 500–650 nm respectively. Chl a is the integral component of all photosynthetic machinery in all oxygenic photoautotrophs, and makes the maximum portion of the core and reaction center (pigment–protein complexes), while Chl b or Chl c in light harvesting antennae, as an accessory to widen light absorption range. Besides the chlorophylls, carotenoids are functions as accessory light-harvesting pigments in photosynthetic apparatus to transfer excitation energy to Chl a. They also make the structural components of the pigment–protein complexes of the light-harvesting antenna and reaction center. The most important role of carotenoids is the protection of photosynthetic machinery from the harmful effect of excess irradiance, chlorophyll triplets and reactive oxygen species.
Biofuel production from algal biomass
Published in Ozcan Konur, Bioenergy and Biofuels, 2017
Jonah Teo Teck Chye, Lau Yien Jun, Lau Sie Yon, Sharadwata Pan, Michael K. Danquah
In addition to nutrients such as phosphorus, nitrogen, potassium, zinc, and calcium, microalgal cultivation requires water, carbon dioxide, and sunlight to produce biomass through photosynthesis, by transforming solar energy into organic chemical energy stored in the microalgal cells. Three major types of microalgae cultivation techniques have been established based on their growth conditions: photoautotropic, heterotrophic, and mixotrophic cultures. Photoautotrophic cultivation utilizes light as the sole energy source that is converted to chemical energy through photosynthetic reactions. Conversely, heterotrophic production requires organic carbon materials as carbon and energy source to simulate growth. In mixotrophic cultivation, the organisms are able to thrive either autotrophically or heterotrophically, depending on the concentration of organic compounds and available light intensity. Among the aforementioned methods, photoautotrophic production is most widely used because it is economically feasible and suitable for large-scale algal biomass production. The choice of microalgal cultivation system from the most commonly available ones, whether open, closed, or hybrid, is made based on the products and the strains to be cultivated (Gambelli et al., 2017; Narala et al., 2016).
Biofuel and Biochemical Production by Photosynthetic Organisms
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
Although photoautotrophic microorganisms are attractive as mentioned above, one of the major drawbacks is its slow growth rate, and slow metabolite production rate as compared to the heterotrophic microorganisms such as E. coli and S. cerevisiae. In general, the time frames for the cultivation of plants are on the order of months, and those of photosynthetic microorganisms are on the order of weeks, while those of heterotrophic microorganisms are on the order of days or even on the order of hours. Therefore, most metabolites are typically formed in mg/l in the photosynthetic microorganisms, while some cyanobacterial strains show in g/l. The metabolite production rates are, therefore, one or two orders lower in photosynthetic microorganisms as compared to heterotrophic microorganisms (Angermayr et al. 2015). The performance improvement may be attained by modulating CO2 fixation, metabolic engineering to improve conversion efficiency, and redox balance etc.
Optimizing protocols for microbial induced calcite precipitation (MICP) for soil improvement–a review
Published in European Journal of Environmental and Civil Engineering, 2022
Tong Yu, Hanène Souli, Yoan Péchaud, Jean-Marie Fleureau
MICP is an ubiquitous natural phenomenon (Stocks-Fischer et al., 1999) that occurs with a wide range of microbial species in various environments (soils, oceans, freshwaters, saline lakes, etc.) (Hammes et al., 2003; Wei et al., 2015). There are three groups of microorganisms that can be involved in the precipitation of calcium carbonate. One group is that of photosynthetic microorganisms (such as cyanobacteria and microalgae), which is photoautotrophic. The other two are heterotrophic, and are related to sulphate cycle (sulphate-reducing bacteria) and nitrogen cycle (such as nitrate reducing bacteria and ureolytic bacteria), separately (Al-Salloum et al., 2017; De Muynck et al., 2010).
Current research and perspectives on microalgae-derived biodiesel
Published in Biofuels, 2020
Kartik Singh, Deeksha Kaloni, Sakshi Gaur, Shipra Kushwaha, Garima Mathur
A carbon source is essential in algal growth and reproduction. Photoautotrophic cultivation means utilizing light as the sole source of energy that is further converted to chemical energy through photosynthetic reactions [50]. Other microalgal strains may use organic carbon (heterotrophic cultivation); however, this mode of production is only useful to produce high-value compounds. The mixotrophic nutrition mode is the combination of autotrophic and heterotrophic mechanisms.