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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Microalgae and cyanobacteria are the first organisms in the oceanic food chain and are essential producers of oxygen and effective carbon dioxide traps. They are traditional sources of food proteins for Aztec, African and Asian populations, and some of them have even acquired the status of superfoods. Microalgae reviews the biological, ecological and biochemical characteristics of microalgae and cyanobacteria. They are true cellular factories, producing substances of interest such as original pigments, proteins and polysaccharides with biological activities. Their use covers many sectors of human activity including aquaculture, livestock breeding, agri-food, and human and veterinary medicine. This book presents their mode of production and the transformation processes that are applied to them, as well as the traditional and future valorization of algae. As they are a source of lipids and fatty acids, microalgae have become the focus of attention for the development of green fuels, such as biofuel.
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Table of Contents
Cover
Title Page
Copyright
Preface
Acknowledgements
Introduction
1 Biology and Ecology of Microalgae
1.1. Biological characteristics
1.2. Ecological features
2 Production Techniques
2.1. Production by harvesting in the natural environment
2.2. Production by culture in open systems
2.3. Production by culture in a closed system
3 Food Valorizations
3.1. Animal feed
3.2. Human food
4 Valorized Molecules
4.1. Polysaccharides
4.2. Proteins and enzymes
4.3. Non-protein pigments
4.4. Fat, sterols and fatty acids
4.5. The special case of biofuel
4.6. Other applications
5 Extraction Processes
5.1. Conventional processes
5.2. Enzymatic hydrolysis
5.3. Other methods
6 Biotechnological Approaches
6.1. Biorefinery
6.2. Physiological forcing
6.3. Genetic transformation
Conclusion
References
Index
End User License Agreement
List of Illustrations
Introduction
Figure I.1. Mechanisms of primary and secondary endosymbiosis to trace the evolu...
Figure I.2. Synthetic phylogenetic tree redistributing the main groups of algae ...
Chapter 1
Figure 1.1.
Cellular organization of the microalga
Chlamydomonas sp. (source: Po...
Figure 1.2.
Cellular organization of the microalga
Chlorella sp. (source: Pouchu...
Figure 1.3.
Frustule (epivalve and hypovalve) of the diatom
Nitzschia sp. visual...
Figure 1.4.
Example of a central diatom
Skeletonema sp. visualized by a scanning...
Figure 1.5.
Example of a pennate
Haslea ostrearia diatom visualized by a scannin...
Figure 1.6. Haslea ostrearia, pennate diatom, responsible for the greening of oy...
Figure 1.7.
Example of toxins produced by dinoflagellates (okadaic acid)
Figure 1.8. Porphyridium cruentum (photo credit © Petit A., 2019). For a color v...
Figure 1.9. Spirulina platensis
(
Arthrospira platensis) (photo credit © Jubeau S...
Figure 1.10. Role of phytoplankton in the biogeochemical cycle of the ocean (sou...
Figure 1.11. Examples of facades colonized by microalgae (photo credit © Fleuren...
Figure 1.12. Aerolization phenomenon causing the presence of algal particles in ...
Chapter 2
Figure 2.1.
Harvesting of the
Spirulina bloom on the shores of Lake Chad (photo ...
Figure 2.2.
Proliferation of the alga
Dunaliella salina in salt marshes in the C...
Figure 2.3. Raceway-type basin (photo credit © Braud J.-P., 2020). For a color v...
Figure 2.4. Representation of the open culture system of microalgae in a raceway...
Figure 2.5. Haslea ostrearia microalgae culture and greening facility of the oys...
Figure 2.6.
Growing tray of the microalga
Haslea ostrearia (500 L) under horticu...
Figure 2.7.
Oyster greening basin with the addition of
Haslea ostrearia culture ...
Figure 2.8.
Oyster verdie (
Crassostrea gigas) after consumption in the greening ...
Figure 2.9.
Batch culture of the microalga
Haslea ostrearia
and
Skeletonema cost...
Figure 2.10.
Batch culture in scobalite cylinders of the microalga
Haslea ostrea...
Figure 2.11. Principle of closed system and batch culture (source: Pouchus Y.-F....
Figure 2.12. Vertical tubular photobioreactor illuminated by LED lamps (photo cr...
Figure 2.13.
Horizontal tubular solar photobioreactor growing
Porphyridium cruen...
Figure 2.14.
Vertical tubular solar photobioreactor growing
Chlamydomonas sp. (p...
Figure 2.15.
Vertical planar photobioreactor of the Subitec culture type of
Tiso...
Chapter 3
Figure 3.1. Drying Spirulina in the open air and in the sun after harvest (photo...
Figure 3.2. Sale of dihé in a Chadian market (photo credit © FAO/Marzot M.). For...
Figure 3.3. Plankton bread (photo credit © Cadour P., 2020). For a color version...
Figure 3.4.
Solmon product incorporating the microalgae
Ondotella aurita (photo ...
Figure 3.5.
Culinary preparation based on Solmon (
Ondotella aurita) (photo credi...
Figure 3.6.
Structure of C-phycocyanin (source: Fleurence and Levine (2018))
Chapter 4
Figure 4.1.
Structure of glucuronic acid (D and L isomers) (source: Grovel 2020)
Figure 4.2. Tetrapyrrole nuclei constituting the chromophores of phycocyanin (a)...
Figure 4.3. Phycobilisome (source: Pouchus Y.-F.). For a color version of this f...
Figure 4.4. Phycoerythrin (photo credit © Fleurence J., 2005). For a color versi...
Figure 4.5. Examples of lipids belonging to the different classes (neutral lipid...
Figure 4.6. Example of n-3 polyunsaturated fatty acid (eicosapentaenoic acid) (s...
Figure 4.7. Main processes and procedures used for the conversion of algal bioma...
Figure 4.8. Distribution by product type (liquid, gas and coal) of the different...
Figure 4.9. Distribution of industrial companies producing biofuel from algal bi...
Figure 4.10.
Structure of tetrodotoxin
Chapter 5
Figure 5.1. Influence of ultrasonication on lipid extraction using organic solve...
Figure 5.2. Influence of pressure at 55°C on the extraction of carotenoids from ...
Figure 5.3. Influence of pressure at 55°C on the extraction of polyunsaturated f...
Figure 5.4. Influence of pressure at 55°C on the extraction of eicosapentaenoic ...
Figure 5.5. Comparison of microwave and ultrasonic methods in fatty acid extract...
Figure 5.6. Effect of pressure on the decay of 50% of the cells in the biomass o...
Figure 5.7. Effect of pressure on the extraction of B-phycoerythrin (B-PE) from ...
Figure 5.8. Effect of freeze-drying on the French press extraction of kinase enz...
Figure 5.9. Effect of enzymatic hydrolysis (cellulases, xylanases, amylases) on ...
Figure 5.10. Effect of enzymatic hydrolysis by autolysin alone or coupled with o...
Figure 5.11. Principle of electroporation applied to the extraction of intracell...
Figure 5.12. Effect of electrochemical extraction as a function of the chemical ...
Chapter 6
Figure 6.1. General principle of biorefinery applied to the valorization of alga...
Figure 6.2.
Effect of CO
2
content on lipid accumulation in the diatom
Chaetocero...
List of Tables
Chapter 1
Table 1.1. Pigment distribution according to the botanical phyla of microalgae (...
Table 1.2. Taxonomic distribution of algae according to the traditional classifi...
Table 1.3. Assessment of the number of cyanobacteria species according to some a...
Table 1.4. Taxonomic distribution of cyanobacteria according to phylogenetic cla...
Table 1.5. Distribution of different categories of phytoplankton by size (from I...
Table 1.6. Some examples of planktonic, benthic and tychoplanktonic marine diato...
Table 1.7. Examples of common centric or pennate diatom species in brackish wate...
Table 1.8. Examples of genera constituting the algal aerial flora (from Sharma a...
Chapter 2
Table 2.1. Species cultivated in raceways for food and cosmetic applications by ...
Table 2.2. Influence of temperature and light intensity on oxygen production (mg...
Table 2.3.
Cost of production of
Porphyridium cruentum biomass by reactor type (...
Table 2.4. Influence of pump type on the growth (+) and cellular fragility of di...
Table 2.5.
Evolution of biomass productivity of
Arthrospira platensis
(
Spirulina...
Table 2.6. Global production status of microalgae and cyanobacteria across all m...
Chapter 3
Table 3.1. Examples of microalgae species used in hatcheries for feeding filter-...
Table 3.2. Main species of microalgae used as fodder algae for feeding shrimp la...
Table 3.3.
Survival rate of larvae of the giant tiger prawn (
Penaeus monodon) ac...
Table 3.4. Main species of microalgae that can have a dual use: live prey as for...
Table 3.5. Examples of the biochemical composition of a few species of microalga...
Table 3.6. Effect of Spirulina content in the diet of rooster chicks on their gr...
Table 3.7.
Examples of some carotenoid-like pigments present in
Chlorella sp. an...
Table 3.8.
Examples of the biochemical composition of Spirulina (
Arthrospira pla...
Table 3.9.
Examples of the mineral composition of Spirulina (
Arthrospira maxima)...
Table 3.10.
Examples of the vitamin composition of Spirulina (
Spirulina platensi...
Table 3.11.
Examples of fatty acid composition of Spirulina (
Spirulina maxima
or
...
Table 3.12.
Examples of the main pigment composition of Spirulina (
Spirulina max...
Table 3.13. Examples of antiviral compounds characterized in selected species of...
Table 3.14. Examples of antibacterial and antifungal activities present in the c...
Table 3.15. Examples of antibacterial and antifungal activities associated with ...
Table 3.16. List of some species of microalgae and cyanobacteria recommended by ...
Chapter 4
Table 4.1. Relative composition of the main oses of the constituent monosacchari...
Table 4.2.
Apparent molecular mass of major exopolysaccharides of the microalgae
...
Table 4.3.
Partial osidic composition of exopolysaccharides of the microalgae
Ch...
Table 4.4.
Percentage of free radical neutralization by
Scenedesmus sp. exopolys...
Table 4.5. Spectral characteristics of major phycobiliproteins of red microalgae...
Table 4.6. SOD stability as a function of temperature and pH for selected specie...
Table 4.7. Examples of total fatty acid contents of some microalgae species (exp...
Table 4.8. Major fatty acids in selected microalgae relatively rich in arachidon...
Table 4.9. Examples of lipid contents of some microalgae species potentially rec...
Table 4.10. Comparison of production costs between biofuel and diesel (based on ...
Table 4.11. Cell growth inhibition activity of human and murine tumor lines by o...
Chapter 5
Table 5.1. Advantages and disadvantages of some extraction methods applied to mi...
Table 5.2. Effect of freeze-drying or lack of freeze-drying on protein extractio...
Table 5.3. Examples of commercial and non-commercial enzyme preparations for lip...
Chapter 6
Table 6.1. Main characteristics of the modes of production of microalgae suscept...
Table 6.2.
Effect of production patterns on biomass productivity of the species
...
Table 6.3. Examples of genetically transformed microalgae and the techniques use...
Table 6.4.
Examples of transgenesis and their areas of application (Beachman
et ...
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Acknowledgements
Introduction
Begin Reading
Conclusion
References
Index
Other titles from iSTE in Ecological Science
End User License Agreement
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Series Editor
Françoise Gaill
Microalgae
From Future Food to Cellular Factory
Joël Fleurence
First published 2021 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd
27-37 St George’s Road
London SW19 4EU
UK
www.iste.co.uk
John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
USA
www.wiley.com
© ISTE Ltd 2021
The rights of Joël Fleurence to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2021938404
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN 978-1-78630-587-9
Preface
Unicellular algae and cyanobacteria are unstoppable actors of life on Earth. They are responsible for the production of half of the oxygen present on our planet. Independently of this major ecological role, microalgae are true cellular factories at the origin of the synthesis of various metabolites of interest for human activity. In particular, they produce original pigments, such as phycobiliproteins, polysaccharides, enzymes, as well as lipids and fatty acids with a long carbon chain, whose valorization as biofuels opens up a new way of valorizing these microorganisms. In addition to the biotechnological uses resulting from this cell plant concept and the resulting biorefinery, microalgae also constitute a food resource for human and animal nutrition.
The purpose of this book is to take stock of the biological and ecological characteristics of microalgae, whether marine, freshwater or even atmospheric. Cyanobacteria (e.g. Arthrospira sp. or Spirulina sp.) are also discussed, as they have long been referred to as “blue algae” under the botanical name of Cyanophyceae.
This book also assesses the production methods and current applications of microalgae and cyanobacteria, whether in the food or biotechnology fields. As far as food applications are concerned, the current uses of microalgae in animal and human nutrition in the form of food supplements are presented. The prospects for development in these application sectors are discussed in light of economic and regulatory constraints.
The biotechnological valorizations of microalgae as cell factories capable of producing molecules with high added value are also described in this book. The techniques for extracting these molecules and the new approaches for valorization, such as biorefinery, are also discussed. Finally, the biotechnological perspective of using genetically modified microalgae for the production of molecules for therapeutic purposes is developed in light of current advances in research in the field.
May 2021
Acknowledgements
I thank Yves-François Pouchus and Olivier Grovel for their illustrations.
Introduction
Cyanobacteria and microalgae are, from a logical chronological point of view, at the origin of oxygen production by photosynthetic means on our planet. Oxygen photosynthesis by cyanobacteria probably occurred 3 billion years ago (Sardet 2013). The appearance of the first eukaryotic cells, including microalgae, is estimated to have occurred 1.5–2 billion years ago. The extent of algal biological diversity in the ocean has long been unknown (Sournia et al. 1991). The number of microalgae species is still not definitively established, and the figures given in the scientific literature range from 70,000 to 150,000 species. Conversely, high estimates suggest a million species (De Vargas et al. 2012; Nef 2019). Such a varied and not always easily accessible biodiversity still poses problems for biologists in terms of censusing, thus explaining the discrepancy in the figures mentioned above. This difficulty has also arisen in the establishment of a classification system to list microalgae in distinct botanical groups (see section 1.1.2). The traditional classification initially based on the pigment composition of microalgae has established three major taxonomic groups or phyla that are commonly referred to as “green algae”, “red algae” and “brown algae”. Cyanobacteria, long considered as algae, were classified as “blue algae”. However, the pigmentary criteria have not always been sufficient to classify the algae and report their evolutionary course. Other characteristics, such as the nature of the endosymbiosis at the origin of the chloroplast (primary or secondary endosymbiosis) (see Figure I.1), have enriched the classification by making it possible to propose new taxonomic groups. This is notably the case for the Glaucophytes group, whose chloroplast is the result of primary endosymbiosis but has retained certain important ancestral characteristics, such as the presence of a peptidoglycan wall between two membranes. This characteristic is effectively shared between these organisms and cyanobacteria (Lecointre and Le Guyader 2016). However, Glaucophytes are microalgae that are not very widespread and are found mainly in fresh water (lakes, swamps and ponds) (Lecointre and Le Guyader 2016). These organisms, which are not subject to valorization, will not be treated in the rest of this book.
Figure I.1.Mechanisms of primary and secondary endosymbiosis to trace the evolutionary course of certain groups of algae (source: Pouchus Y.-F.). For a color version of this figure, see www.iste.co.uk/fleurence/microalgae
Since phylogenetic classification is mainly based on molecular criteria, such as ribosomal DNA, it has broken up the main groups previously established by the traditional classification (see Figure I.2). Nevertheless, for obvious reasons of convenience, the classifier remains attached to and still uses the denominations of red, brown or green algae to describe the algal biomass.
Microalgae show high metabolic plasticity and a natural aptitude for horizontal gene transfer. This last property is at the origin of the extremely diversified evolution of algae. These two natural characteristics of microalgae also make them valuable biotechnological aids for the production of molecules of interest, such as recombinant proteins (Cadoret et al. 2008) or biofuel (Maeda et al. 2018). Finally, microalgae, such as Chlorella, and cyanobacteria, such as Spirulina, are already used in animal and human food, even if, in the latter case, it remains more of a food supplement than a food in its own right.
Figure I.2.Synthetic phylogenetic tree redistributing the main groups of algae (source: Pouchus Y.-F.). For a color version of this figure, see www.iste.co.uk/fleurence/microalgae
1Biology and Ecology of Microalgae
1.1. Biological characteristics
1.1.1. General characteristics
Microalgae are mainly photo-synthetic single-celled organisms living in aquatic environments (marine, brackish, fresh water) or humid or aerial terrestrial environments (atmosphere, soils, trees, building facades, etc.) (Sharma et al. 2006). They can also associate together to form colonies or undifferentiated multicellular organisms. The morphology and size of microalgae vary greatly according to species and taxonomic groups.
Microalgae are eukaryotic organisms that possess the main characteristics of the vegetable eukaryotic cell. They can be flagellated as in the case of algae belonging to the genus Chlamydomonas (see Figure 1.1) or not (see Figure 1.2). As eukaryotes, microalgae can be distinguished from cyanobacteria, which are prokaryotic organisms with a long life span and are called “blue-green algae” or Cyanophyceae. Spirulina (Arthrospira sp.), a well-known representative of this group, is, therefore, a photosynthetic bacterium and not an alga, as is often stated in commercial communication (Fleurence 2018).
Microalgae are also characterized by a great morphological diversity. This is the case of diatoms, which are distinguished from other algae by the presence of a siliceous shell called a frustule and whose architecture differs according to the species considered (see Figure 1.3) (Loir 2004). This unique morphological feature is the biological signature of diatoms, which are also known as “siliceous algae”. This morphological heterogeneity is also found in size since microalgae generally vary in size from less than 1 μm to 1 mm. The smallest size, 0.8 μm, is observed for the marine species Ostreococcus tauri (Borowitzka 2018a).
Figure 1.1.Cellular organization of the microalga Chlamydomonas sp. (source: Pouchus Y.-F.). For a color version of this figure, see www.iste.co.uk/fleurence/microalgae
Figure 1.2.Cellular organization of the microalga Chlorella sp. (source: Pouchus Y.-F.). For a color version of this figure, see www.iste.co.uk/fleurence/microalgae
1.1.2. The different groups in traditional and phylogenetic classification
Like all organisms, microalgae are classified into several taxonomic groups according to traditional or phylogenetic systematics. The traditional systematics establishes botanical phyla based on the pigment position of the microalgae. The pigment criterion, according to its nature, is an agglomerating or discriminating character. Thus, all algae, micro- or macroalgae, have a common pigment: chlorophyll a. This pigment is also present in cyanobacteria and terrestrial plants. The presence of additional pigments, called supernumerary pigments, is used as a distinguishing criterion to define the main algal phyla (see Table 1.1). These phyla, of which there are three, are, respectively, the phylum of Chlorophyta (green algae), Chromophyta (golden-brown algae) and Rhodophyta (red algae). Each phylum consists of a single phylum branch, as is the case for Chlorophyta and Rhodophyta, or three separate branch, as is the case for Chromophyta (see Table 1.2). Each branch is itself divided into several classes. The number of classes may vary according to the criteria used by the different authors. This is particularly true for Rhodophyta, where complementary criteria to the pigmentary characteristics (nature of the starch, life cycle and reproduction, etc.) lead to the distinction of seven classes instead of one.
Table 1.1.Pigment distribution according to the botanical phyla of microalgae (from Morançais et al. (2018))
Phylum
Common pigment
Supernumerary pigments
Chlorophyta
Chlorophyll a
Chlorophyll b
Chromophyta
Chlorophyll a
– Chlorophylls c, e
– Excess carotenoids
(β-carotene, fucoxanthin, zeaxanthin, etc.)
Rhodophyta
Chlorophyll a
– Chlorophyll d
– R or B Phycoerythrin
– Phycocyanin
– Allophycyanin
1.1.2.1. Chlorophyta
The phylum of Chlorophyta is characterized by the simultaneous presence of chlorophylls a and b. This group comprises 6,429 species and is divided into 11 distinct classes (Sexton and Lomas 2018) (see Table 1.2 where only the main ones are mentioned):
– the Chlorophyceae class with 3,653 species represents the main phylum taxonomic group. Microalgae belonging to the genera
Chlamydomonas, Volvox
and
Dunaliella
are the most representative members. The alga
Dunaliella
sp. is also valued in animal and human food (see
sections 3.1
and
3.2
);
– the Ulvophyceae class mainly includes macroalgae and some microscopic unicellular forms (Sexton and Lomas 2018);
– the Trebouxiophyceae class includes the genus
Chlorella
, a microalga valued in particular as a food supplement in human nutrition.
Table 1.2.Taxonomic distribution of algae according to the traditional classification enriched with the addition of secondary traits such as endosymbiotic origin plastid (based on Loir (2004) and Sexton and Lomas (2018))
Phylum
Branch
Classes (number of species)
Chlorophyta (green algae)
Chlorophycophyta
– Chlorophyceae (3,653)
– Ulvophyceae (1,725)
– Trebouxiophyceae (794)
– Prasinophyceae (105)
– Mamiellophyceae (18)
Chromophyta (golden-brown algae)
Pheophycophyta
Pheophyceae (2,040)
Chrysophycophyta
– Bacillariophyceae (11,000–100,000) (diatoms)
– Chrysophyceae (670)
– Xanthophyceae (450–600)
Pyrrophycophyta
Dinophyceae (3,327)
Rhodophyta (red algae)
Rhodophycophyta
Rhodophyceae
1.1.2.2. Chromophyta
The Chromophyta phylum is divided into three phylum branches, each of which is subdivided into several distinct classes (see Table 1.2). In the branch – of Pheophycophyta – there is one class, that of Phaeophyceae. Phaeophyceae include 2,040 species and are known as brown algae. They do not include unicellular forms, except for the presence of biflagellated spores during the reproductive cycle of these algae, the best-known members of which belong to the genera Macrocystis, Laminaria and Fucus.
In the Chrysophycophyta branch, there are three well-classified classes. Among them, the class of Bacillariophyceae is one of the most studied for its biological diversity and ecological importance. This class, known as diatoms, includes unicellular brown-yellow algae with sizes ranging from 2 μm to 1 mm (Loir 2004). The number of species of diatoms is estimated to be at least 11,000, but some authors estimate the number to be around 100,000 (Mann and Vanormelingen 2013). Diatoms are morphologically characterized by the presence of an external envelope of siliceous nature called a frustule. This name is derived from the Latin frustulum, which means “piece” or “small end” (Round et al. 1990). The frustule is a shell composed of two valves called the epivalve and hypovalve (see Figure 1.3). This structural element has different shapes and symmetries in different species.
The frustule is responsible for the dichotomous separation of diatoms into two distinct groups. When the latter is in the form of a disc or tube with radial symmetry, the diatoms are referred to as centric or central diatoms (see Figure 1.4). On the other hand, diatoms with a more or less elongated frustule and mainly showing bilateral symmetry are classified as pennate or pennal diatoms (see Figure 1.5).
The species Haslea ostrearia involved in the greening mechanism of oysters (see section 3.1) belongs to the latter group (see Figure 1.6). Diatoms are photosynthetic organisms, but some species living in light-poor environments are heterotrophic for carbon. These diatoms incapable of synthesizing chlorophyll represent less than 10 species belonging to the genera Nitzschia and Hantzschia (Hantzschia achroma) (Li and Volcani 1987).
Figure 1.3.Frustule (epivalve and hypovalve) of the diatom Nitzschia sp. visualized by a scanning electron microscope (SEM) (photo credit © Gaudin P., 2010)
Figure 1.4.Example of a central diatom Skeletonema sp. visualized by a scanning electron microscope (SEM) (photo credit © Petit A., 2010)
Figure 1.5.Example of a pennate Haslea ostrearia diatom visualized by a scanning electron microscope (SEM) (photo credit © Petit A., 2010)
Figure 1.6. Haslea ostrearia, pennate diatom, responsible for the greening of oysters (photo credit © Petit A., 2019). For a color version of this figure, see www.iste.co.uk/fleurence/microalgae
Chrysophyceae or golden yellow-brown algae include about 670 species. Although autotrophic for carbon, some of them are bacterivorous and have very different morphologies, ranging from filamentous to capsular or even spherical (Sexton and Lomas 2018). The main representatives belong to the genera Dinobryon, Ochromonas and Phaeoplaca or Tisochrysis.
The Xanthophyceae, known as yellow-green algae, are well listed in the Chromophyta phylum. They do not possess chlorophyll b, which is the pigmentary criterion shared by all Chlorophyta. The yellow color is due to the presence of an excess of yellow xantho phyllum (Sharma 1986). We find in this class the algae belonging to the genera Vaucheria and Chloromeson.
The Pyrrophycophyta branch is composed of several classes, the number of which varies according to the authors and some of which are considered today as obsolete. It should simply be remembered that this branch includes the class Dinophyceae (Dodge 1985), whose organisms, known as dinoflagellates, have a very particular position in the traditional classification. These organisms have often been considered as brown algae, but their evolutionary history based on mechanisms of secondary endosymbiosis suggests that they derive from an ancestor of the Rhodophyta type (Perez 1997; Nef 2019). Moreover, dinoflagellates have the particularity, in addition to an excess of β-carotene, of possessing a red-colored pigment, peridinin (Perez 1997). This specificity is at the origin of the red coloration of waters when dinoflagellates are present in large numbers in the environment. Apart from the above-mentioned characteristics, dinoflagellates present another particularity that makes their classification delicate. Indeed, this class constitutes a mixotrophic ensemble: 50% of the species are autotrophic for carbon, the others are heterotrophic for this element (Borowitzka 2018a, 2018b). They can therefore be linked to the animal kingdom or to the plant kingdom according to this trophic characteristic. These are organisms whose size fluctuates between 10 μm and 2 mm (Spector 1984). Many species of dinoflagellates are involved in the phenomenon of “red tides”. They mainly belong to the genera Alexandrium, Dinophysis, Gymnodinium and Prorocentrum (Faust and Gulledge 2002). They can produce toxins that affect invertebrates, fish and mammals. These toxins, the most well-known of which are DSP, for diarrhetic shellfish poisoning (see Figure 1.7), are at the origin of poisoning during the consumption of contaminated shellfish.
Figure 1.7.Example of toxins produced by dinoflagellates (okadaic acid)
(source: Grovel O.)
