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Introduction to cyanobacteria
Published in Ingrid Chorus, Martin Welker, Toxic Cyanobacteria in Water, 2021
Leticia Vidal, Andreas Ballot, Sandra M. F. O. Azevedo, Judit Padisák, Martin Welker
A number of cyanobacterial taxa can (facultatively) produce so-called aerotopes that are clearly visible in microscopy as light-refracting structures. Aerotopes (sometimes incorrectly named “gas vacuoles” – they are not vacuoles in the cytological sense) are bundles of cylindrical protein microstructures that form the gas vesicles. These vesicles are filled with air entering the lumen by diffusion (see Walsby (1994) for an extensive review). Gas vesicles have a density of about one-tenth of that of water and thus render the entire cells less dense than water, providing buoyancy and making them float or emerge to the water surface (see Section 3.2). The gas vesicles measure some 75 nm in diameter and up to 1.0 µm in length. The cylinders, capped by conical ends, are formed by a single wall layer of 2 nm thickness. The distribution of aerotopes within the cells is characteristic for individual taxa and can be used for identification by microscopical examination, but they can disintegrate after fixation with Lugol’s solution (see Chapter 13).
Microbial Biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular chromosome located in the cytoplasm in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome with associated proteins and RNA. The order Planctomycetes are an exception to the general absence of internal membranes in bacteria because they have a membrane around their nucleoid and contain other membrane-bound cellular structures. Like all living organisms, bacteria contain ribosomes to produce proteins, but the structure of the bacterial ribosome is different from those of eukaryotes and archaea. Some bacteria produce intracellular nutrient storage granules such as glycogen, polyphosphate, or sulfur. These granules enable bacteria to store compounds for later use. Certain bacterial species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles, which they use to regulate their buoyancy, allowing them to move up or down into water layers with different light intensities and nutrient levels.
Cells and Cellular Aggregates
Published in Volodymyr Ivanov, Environmental Microbiology for Engineers, 2020
Granules of storage polymers, glycogen, or poly-β-hydroxybutyrate (PHB) are present in the cytoplasm. Granules of elemental sulfur are found in the cytoplasm of phototrophic or sulfur-oxidizing bacteria. Gas vesicles are intracellular hollow spaces in cells providing cell buoyancy. Magnetosomes are magnetite granules of specific shape. The accumulation of polyphosphate granules in some bacterial cells is the main approach for the bioremoval of phosphorus from wastewater.
Reducing surface accumulation of Aphanizomenon flos-aquae using wetland water to increase cellular turgor pressure and interfere with buoyancy regulation
Published in Lake and Reservoir Management, 2018
Arick C. Rouhe, John G. Rueter
Surface accumulation is a key advantage for the dominance of buoyancy regulating cyanobacteria (Reynolds et al. 1987) but CyanoHABs that accumulate at the surface of lakes can have adverse effects on lake ecology (Scheffer et al. 1997, Dokulil and Teubner 2000). Buoyant cyanobacteria accumulate at the surface of a water body by forming gas vesicles in individual cells (Oliver 1994). The main factors that trigger gas vesicle formation are low light and high phosphorus availability (Konopka et al. 1987, Walsby 1994). Once triggered, gas vesicles are often formed in excess, leading to dense accumulations of cyanobacteria cells, filaments, and colonies at the water surface that can persist for days, weeks, and months (Zohary and Roberts 1990, Walsby et al. 1991). A dense surface accumulation drastically reduces light availability in the lower water column (Scheffer et al. 1997) creating a low-light environment that favors cyanobacteria growth (Zevenboom and Mur 1980, Dokulil and Teubner 2000). Experimental tests of competition between phytoplankton taxa show that cyanobacteria outcompete diatoms and green algae in stable, low-light conditions (Zevenboom and Mur 1980, Huisman 1999, Huisman et al. 2004). Thus, shading from surface accumulation creates conditions that favor cyanobacteria propagation over other competing phytoplankton taxa, leading to an unhealthy system with low phytoplankton diversity, diminished zooplankton grazing, and poor water quality (Scheffer et al. 1997, Dokulil and Teubner 2000, Llames et al. 2009).
Study on the method and mechanism of pre-pressure coagulation and sedimentation for Microcystis removal from drinking-water sources
Published in Environmental Technology, 2018
Haibing Cong, Feng Sun, Wenjing Chen, Yajun Xu, Wei Wang
The buoyancy produced by gas vesicles is the main reason for Microcystis to float on the surface of water. In order to improve the removal efficiency of Microcystis by coagulation and sedimentation, the buoyancy of gas vesicles should be eliminated. Microcystis is a kind of unicellular organism with a cell diameter of 4–6.5 μm [12,13]. The colloidal substances wrapped on the surface of Microcystis cells attaches thousands of cells together and forms particles with a diameter of up to 1000 μm [14,15]. Microcystis cell is composed of cell wall, cell sap, and gas vesicles. The main component of cell wall is peptidoglycan. Cell sap contains exposed DNA molecules and photosynthetic products, mainly cyanophycean starch and lipid granule. The gas vesicles are columnar bubbles wrapped with protein walls, which have tapered ends and hexagonal cross-section with an inner circle diameter of 65–115 nm and length of 200–1200 nm [16]. The gas could pass through the wall of gas vesicles, but the liquid would be stopped by the hydrophobic inner surface, thereby forming a hollow structure to store the oxygen produced by photosynthesis [17,18]. Normally, cells could be suspended when the volume fraction of gas vesicles is 1–2% [19]; moreover, the volume fraction of gas vesicles in Microcystis is 2.3–7% [20]. The buoyancy produced by gas vesicles is necessary for Microcystis suspending in upper layer of water to obtain the light for photosynthesis [21,22]. The sustainable pressure of gas vesicles is 0.4–0.7 MPa, and gas vesicles would collapse when the external pressure is more than that [23]. The sustainable ability of gas vesicles to bear external pressure is affected by the factors such as gene, gas vesicle size, and other factors [24,25].
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].