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Microalgae II: Cell Structure, Nutrition and Metabolism
Published in Arun Kumar, Jay Shankar Singh, Microalgae in Waste Water Remediation, 2021
Microalgae include prokaryotic groups—cyanobacteria and prochlorophytes; and eukaryotic groups—red algae, green algae, diatoms and dinoflagellates, etc. Prokaryotic cells have a thin plasma membrane, the peptidoglycan cell wall could have sheaths, capsules and slime as an outer covering of the cell wall. They lack membrane-bound organelles like nucleus and the genetic material suspended freely in the cytoplasm. The cyanobacterial cell contains unstacked thylakoids in their chloroplasts as photosynthetic apparatus and also contains phycobilioproteins accessory pigments. They often perform asexual reproduction through binary fission or multiple fission and special structures like hormogonia and akinetes. The presence of nitrogen fixing cells i.e., heterocyst makes them cyanobacteria, a distinctive and important group of the microalgal world.
Biochemical Pathways for the Biofuel Production
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
Indirect biophotolysis involves the use of reducing equivalents derived from the endogenously stored carbohydrates. These carbohydrates are formed during the CO2 fixation of the photosynthesis process thus involving the indirect use of sunlight. This process is mostly predominant in cyanobacteria. Like direct biophotolysis, indirect biophotolysis also can be performed in single-stage and two-stage processes (Figure 4.3). In the single-stage indirect biophotolysis, the oxygen evolution reaction and the hydrogen evolution reaction are separated by spatial arrangements (Manish and Banerjee 2008). It is carried out usually by nitrogen-fixing cyanobacteria comprised of specialized cells known as heterocysts (Figure 4.3a). The CO2 fixation occurs in the vegetative cells, while the nitrogen fixation and hydrogen evolution occurs in the heterocysts. Due to the absence of O2-evolving PSII in heterocysts, an anaerobic condition prevails which helps in nitrogen fixation and hydrogen production by oxygen sensitive nitrogenases. Moreover, the cell walls of heterocysts are impermeable to oxygen and thus do not allow the oxygen coming from the vegetative cells to enter inside. Therefore, the environment of heterocyst is most suitable for hydrogen production. Anabaena sp. and Nostoc sp. are a few examples of heterocystous cyanobacteria. Two-stage indirect biophotolysis mostly occurs in non-N2-fixing non-heterocystous cyanobacteria such as Synechocystis sp., Synechococcus sp., and Gloebacter sp. In these organisms, hydrogen production is mediated by hydrogenases by maintaining temporal separation (separation depending on time of expression) of hydrogen production from the oxygen-evolving photosynthesis (Figure 4.3b). This process takes place by using the diurnal (day and night) cycle (i.e., during the day CO2 fixation occurs through photosynthesis and during the night hydrogen is produced through fermentation of this accumulated carbohydrate.
The Potential of Microalgae for Environmental Biotechnology
Published in Pau Loke Show, Wai Siong Chai, Tau Chuan Ling, Microalgae for Environmental Biotechnology, 2023
Fazril Ideris, Mei Yin Ong, Jassinnee Milano, Mohd Faiz Muaz Ahmad Zamri, Saifuddin Nomanbhay, Abd Halim Shamsuddin, Teuku Meurah Indra Mahlia, Pau Loke Show
As microalgae are excellent at capturing carbon dioxide from the atmosphere, the direct application of microalgae biomass in agriculture would help crops to have a better growth and productivity (Salih and Salih 2011). The use of microalgae biomass as a soil additive increases the level of organic carbon content in soil. This is important as the depletion of organic carbon leads to degradation of the soil’s fertility, which is common for agricultural lands (Stavi and Lal 2015). Apart from that, the addition of microalgae biomass to soil would improve water retention and structure of the soil. Acting as soil conditioners, the spread of land desertification may be reversed with direct application of microalgae biomass (Rossi et al. 2017). Dry Acutodesmus dimorphus biomass was used as a biofertilizer for tomato plants, and it had shown encouraging effects on seed germination, plant growth, and fruit yield (Garcia-Gonzalez and Sommerfeld 2016). In another study, the effects of application of liquid fertilizer prepared from Chorococcum sp. biomass to four different crops (Capsicum annuum, Solanum lycopersicum, Vigna radiata, and Cucumis sativus) were studied. It was discovered that the application of low-concentration liquid fertilizer (20% concentration) is enough to provide significant results on the growth, root and shoot lengths, number of leaves, and number of lateral roots of all four plants. This proves that low-cost liquid biofertilizer could be a potential substitute to the expensive synthetic fertilizer (Deepika and MubarakAli 2020). Moreover, dried biomasses from six microalgae/cyanobacteria species were used as slow-release biofertilizers in the cultivation of rice seedlings, resulting in an improved leaf width and shoot growth (Mukherjee et al. 2016). Cyanobacteria-based biofertilizers are known as diazotrophes (capable of fixing nitrogen), while enhancing the aeration within soil and supplying vitamin B12 to the crops. Nitrogen is fixed in their cell which is known as heterocyst, before providing the important element to crops (Berman-Frank, Lundgren, and Falkowski 2003). Among the most common diazotrophes are Anabaena variabilis, Calothrix sp., Tolypothrix sp., Aulosira fertilisima, and Nostoc linckia, which are normally found in rice fields. It is reported that as much as 60 kg/ha/season of nitrogen can be fixed by Anabaena (Chittora et al. 2020). Furthermore, these biofertilizers were also used in cultivations of various crops such as oat, chili, corn, lettuce, tomato, barley, oats, cotton, and sugarcane (Thajuddin and Subramanian 2004). Recent studies involving the usage of these microorganisms in agriculture are presented in Table 2.4.
The role of silver nanoparticles biosynthesized by Anabaena variabilis and Spirulina platensis cyanobacteria for malachite green removal from wastewater
Published in Environmental Technology, 2021
Gehan A. Ismail, Nanis G. Allam, Walaa M. El-Gemizy, Mohamed A. Salem
Several possible reasons have been reported to explain the mechanism leading to extracellular or intraellular formation of AgNPs by algal biomass. Generally, the first step involved the trapping of Ag+ ions by the negatively charged carboxylate groups on the cell surface, possibly via electrostatic interaction. Reduction of AgNO3 may be produced intracellularly by the electron transport chain reactions within the cyanobacterial cells [44]. In this respect, Ag+ ions could be reduced by an intracellular electron donor, mainly NADH-dependent reductase [5,10] which gains electrons from the oxidtion of NADH to NAD+. Thus, the enzyme is oxidised by concurrent reduction of Ag+ ions to form Ag metal in the nanometre range [45]. Nitrate, in turn, was reduced to nitrite and ammonia then got fixed into glutamine by cyanobacteria metabolic processes. These reported explanations support the results of the present study since the TEM images of A. virabilis and S. platensis species (Figure 2(c,d)) showed the accumulation of AgNPs inside the cells of A. virabilis (heterocystous species) and S. platensis (non- heterocystous species). In this regard, Brayner et al. [11] emphasised the role of nitrogenase and hydrogenase enzymes localised in the heterocyst or in the vegetative cell membranes of Calothrix, Anabaena and Leptolyngbya cyanobacterial cultures as reducing agents for AgNO3 and for the formation of extracellular AgNPs around the cells.
Identification of Phytoplankton from Fresh Water and Growth Optimization in Potent Algae by Response Surface Methodology for Enhanced Biomass Production
Published in Smart Science, 2020
Santhosh Sigamani, Mohammed Habeeb Ahmed, Hemalatha Natarajan, Dhandapani Ramamurthy
The size of Chlorella sp. is spherical and single celled organism with a diameter of 2–10 micrometer [28] that falls under the order Chlorococcales and Chlorellaceae family [29]. In a growth condition of microalgae containing cellulose based cell wall that varies in its thickness and composition [30]. A microalgal strain can morphologically vary with age factors and the conditions of culture [31]. The second isolate in the present study belongs to the genus Oscillatoria which is a dominant cyanobacterium (Cyanophyceae) that grows in various habitats [32]. The thallus that is made up of single trichome (filament). This cyanobacterium are blue-green to violet-red in appearance where green color represents Chlorophyll a as carotenoids and accessory pigments, Blue color is found due to phycobiliprotein named phycocyanin. This distinct feature makes it different from other cyanobacteria. They also differ based on its motility and ability to conduct the anoxygenic photosynthesis. The long filamentous structures appear as discoid and surrounded by cell wall making it devoid of heterocyst. To survive their position in water planktonic species have gas vesicles. These gas vesicles are cytoplasmic inclusions that enable buoyancy to adjust their floating nature in water bodies in search of a suitable niche for survival and growth. Due to its oscillating movement this cyanobacteria derives its name as Oscillatoria. The phototactic movements caused due to slime secretion or surface undulation are also reported [33,34]. The third isolate Chlorococcum sp. had vegetative cells in solitary or temporary groups of indefinite form, not embedded in gelatin. Cells are ellipsoidal to spherical and vary in size and their cell wall is smooth. Their chloroplast is parietal with or without a peripheral opening but with one or more pyrenoids. Cells are generally uninucleate or multinucleate prior to zoosporogenesis. Reproduction is by zoospores, aplanospores, or isogametes. The cells are motile and contain two flagella that remained ellipsoidal after motility ceases. Physiological studies of its several species have determined the effect of various nutrients and inhibitors on growth. A serological study was performed to determine the relationship between Chlorococcum and Tetracystis which differs morphologically only in the ability of the latter to form tetrads by desmoschisis [35].