Arthrospira (Spirulina) 2 5 Claudio Sili , Giuseppe Torzillo and Avigad Vonshak
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Arthrospira (Spirulina) 2 5 Claudio Sili , Giuseppe Torzillo and Avigad Vonshak Contents Summary Summary ........................................................................................ 677 25.1 Introduction .................................................................. 677 The successful commercial exploitation of Arthrospira because of its high nutritional value, chemical composition 25.2 Morphology................................................................... 678 and safety of the biomass has made it one of the most impor- 25.3 Taxonomy ...................................................................... 686 tant industrially cultivated microalgae. Knowledge of its 25.4 Occurrence and Distribution ...................................... 689 biology and physiology, which is essential for understand- ing the growth requirements of this alkaliphilic organism, 25.5 Physiology ..................................................................... 691 25.5.1 Response to Environmental Factors ............................... 692 has been used in developing suitable technologies for mass 25.5.1.1 Effect of Light on Growth .............................................. 692 cultivation. The relationships between environmental and 25.5.1.2 Light Stress – Photoinhibition ....................................... 692 cultural factors, which govern productivity in outdoor cul- 25.5.1.3 Effect of Temperature on Photosynthesis tures, are discussed in connection with growth yield and and Respiration .............................................................. 692 25.5.1.4 Effect of Temperature on Growth effi ciency. The response of Arthrospira and its modi fi cation and Cell Composition .................................................... 693 under stress is described, together with the strategy of 25.5.1.5 Interaction of Low Temperature osmotic adjustment and the mechanism of internal pH regu- with Light and High Oxygen Concentration .................. 694 lation to alkalinity. The metabolic plasticity of the response 25.5.2 Effect of Salinity on Growth, Photosynthesis and Respiration .............................................................. 695 to disparate environmental stimuli is demonstrated in the 25.5.3 Osmoregulation .............................................................. 695 natural environment, but is also well-expressed in the main- 25.5.4 A rthrospira as an Alkaliphile ......................................... 696 tenance of high productive monoculture in intensive outdoor 25.5.5 How Does Arthrospira Compete in Culture? ................. 696 cultivation systems. 25.6 Mass Cultivation of Arthrospira .................................. 697 While the confused taxonomy of Arthrospira and its 25.7 Market and Application .............................................. 699 relationship with Spirulina has been resolved by study of the ultrastructural feature of trichomes and 16S rRNA sequence References ...................................................................................... 701 analysis, the problem of species de fi nition is still ongoing. However, molecular methods such as total DNA restriction pro fi le analyses of a wide range of strains are helping to resolve this. 25.1 Introduction C. Sili (*) • G. Torzillo This account needs to start with a taxonomic comment. Istituto per lo Studio degli Ecosistemi, CNR , Ever since Arthrospira was fi rst reported in 1852 by Via Madonna del Piano, 10, 50019 , Sesto Fiorentino, Firenze , Italy Stizenberger, many species of this genus of helically coiled e-mail: [email protected] ; [email protected] cyanobacteria have been described and isolated. However, its A. Vonshak classi fi cation has long been a source of confusion. Geitler Microalgal Biotechnology, The Jacob Blaustein Institute ( 1925 ) invalidated the genus Arthrospira in his revision of for Desert Research , Ben-Gurion University of the Negev , Sede Boker Campus, Beersheba , 84990 , Israel the Cyanophyceae and included all regularly helically coiled e-mail: [email protected] Oscillatoriales without fi rm sheaths in the previously described B.A. Whitton (ed.), Ecology of Cyanobacteria II: Their Diversity in Space and Time, 677 DOI 10.1007/978-94-007-3855-3_25, © Springer Science+Business Media B.V. 2012 678 C. Sili et al. genus Spirulina Turpin 1829 . Most authors followed Geitler for a long while, but increasingly researchers realized that 25.2 Morphology genera are distinct and returned to using two names. The evi- dence supporting this was summarized by Castenholz ( 2001 ) The main morphological feature of Arthrospira is the typical and Komárek and Anagnostidis (2005 ) . Many species cur- arrangement of its multicellular cylindrical trichomes in an rently listed as Spirulina should therefore be re-included in open helix usually of relatively large diameter, sometimes Arthrospira and these include all those grown commercially attenuated at the ends, and with evident cross-walls and sold as Spirulina. This material is now known so widely (Fig. 25.1 ). In contrast, Spirulina presents a screw-like under this name that it seems inevitable that the name will trichome, generally with almost closed, uniform and narrow persist; however, it should be written as Spirulina or spirulina diameter screws (0.5–3 m m), cells with cross-walls usually i.e. no italics. invisible at light microscope, without gas vacuoles and with Arthrospira has been reported to exist in environments prominent granules (Fig. 25.2). The trichomes of Arthrospira varying in their osmoticum, temperature and salt concentra- are composed of cylindrical cells that undergo binary fi ssion tions, most being of high alkalinity (Iltis 1969a, b ; Busson in a single plane perpendicular to the main axis. Trichome 1971 ) . Filaments of (true) Spirulina also occur in many of elongation occurs through multiple intercalary cell division these environments, but apparently never forming the blooms along the entire fi lament. Multiplication occurs only by frag- that often occur with Arthrospira . mentation of a trichome, usually in correspondence of a There is great interest in past and present use of Arthrospira necridial cell (Fig. 25.3 ). The mechanism, has been described as a food, though nowadays mostly as a “health” food. in detail for both A. maxima and A. fusiformis by Tomaselli Dangeard ( 1940 ) , Brandily ( 1959 ) and Léonard and Compère et al. ( 1981 ) . It consists in the destruction of an intercalary ( 1967 ) all described how African tribes living along Lake sacri fi cial cell (necridium) that fi rst becomes colourless and Chad collect this alga. The biomass is harvested from water- fi nally biconcave due to the collapse of the lateral septa. bodies near the lake and sun-dried on the shores to produce a However, the presence of necridia become less evident when hardened dark cake called “dihé”, which is broken into small cultures are subject to fast mixing as it occurs in mass cul- pieces and used in different forms by the local populations as tures. In contrast, the fragmentation of Spirulina trichomes part of their daily diet. At about the same time, Arthrospira occurs always without the production of necridic cells was also recorded in the water of Lake Texcoco, Mexico. (Komárek and Anagnostidis 2005 ) (Table 25.2 ) . Here, it had been used as food by the natives living in The trichome width of Arthrospira populations sampled the area (Clément 1968 ) . Travellers to Mexico during the from nature ranges from about 2.5 to 16 m m, while the helix sixteenth century described how the Aztecs used a soft a pitch typically ranges from 0 to 80 m m and its diameter from blue-green material, harvested with fi ne nets from the lake, 15 to 60 m m. The dimensions and other morphological fea- for making a kind of bread called “tecuitlatl” (Ciferri 1983 ) . tures of A . fusiformis (i.e. the well-known commercial It is striking that these two human populations, living far Spirulina platensis) not only vary markedly between popula- apart, discovered the nutritional value of Arthrospira tions, but also within one population (Fig. 25.4 ). Both under independently. laboratory and mass cultivation conditions, the helix architec- Later, attention was refocused on “Spirulina” by the pio- ture (pitch and diameter) is highly dependent on growth and neering work of the Institute Française du Pétrole on environmental conditions. Observations on Arthrospira cyanobacterial blooms in the evaporation ponds of the indus- fusiformis by the authors have shown that morphological trial soda production facility at Lake Texcoco near Mexico variability and trichome motility are especially evident during City. This led to the fi rst detailed study of the growth require- the fi rst weeks following trichome isolation, and that this is ments and physiology of Arthrospira . The Ph.D. research of usually maintained for some years in laboratory liquid culture Zarrouk ( 1966 ) was the basis for establishing the fi rst large- (Fig. 25.5 ). In contrast, morphological variation in A. maxima scale production plant. The work was followed up by several following its isolation is much less marked (Fig. 25.6 ). Both groups in Italy, France and Israel and summarized in a review A. fusiformis (Fig. 25.7 ) and A. maxima typically have abun- by Ciferri ( 1983 ) . The subsequent extensive research on cell dant gas vacuoles, which help to position the organism in the biology, biochemistry and biotechnology has been reviewed water column. They have an important role in the harvesting in books edited by Vonshak