Name: red algae pigments, shapes, and uses
Uploaded: 2025-06-12T09:26:52.000Z
Duration: 1 min 23 s
Channel: JoVE

Les algues rouges ou rhodophytes appartiennent à l’embranchement des rhodophytes dans le règne des Archaeplastida. Ils habitent les écosystèmes terrestres, d’eau douce et marins. Ils sont généralement caractérisés par leur couleur rouge, qui résulte du pigment phycoérythrine présent dans leurs phycobilisomes. Les algues rouges sont phototrophes et utilisent principalement la chlorophylle a pour la photosynthèse. Les algues rouges unicellulaires comprennent les genres Cyanidioschyzon et Galdieria. Ils prospèrent à des températures allant de 30 °C à 60 °C et à des niveaux de pH aussi bas que 0,5 à 4,0. Certaines espèces de Galdieria peuvent même pousser dans l’obscurité totale. Les Cyanidioschyzon merolae ne mesurent que 1 à 2 μm de diamètre et ont l’un des plus petits génomes eucaryotes d’environ 16,5 paires de mégabases. Plusieurs espèces d’algues rouges, comme Polysiphonia, sont filamenteuses et multicellulaires. Certaines espèces d’algues ont une valeur commerciale pour la production d’agents épaississants, tels que la gélose et les carraghénanes. De plus, les espèces Porphyra sont récoltées, séchées et utilisées comme emballages comestibles dans les sushis.

principaux phylums d’algues

Red Algae

Les algues rouges, &#233;galement appel&#233;es rhodophytes, se trouvent principalement dans les milieux marins, bien que certaines esp&#232;ces vivent en eaux douces ou dans des &#233;cosyst&#232;mes terrestres. Ces organismes existent sous forme unicellulaire et multicellulaire, certaines vari&#233;t&#233;s multicellulaires atteignant des tailles macroscopiques.
En tant qu&#8217;organismes phototrophes, les algues rouges contiennent de la chlorophylle a ; toutefois, leurs chloroplastes ne poss&#232;dent pas de chlorophylle b. Elles utilisent &#224; la place des phycobiliprot&#233;ines comme principaux pigments collecteurs de lumi&#232;re, similaires &#224; ceux des cyanobact&#233;ries. La teinte rouge&#226;tre caract&#233;ristique de nombreuses algues rouges est due &#224; la phyco&#233;rythrine, un pigment accessoire qui masque la coloration verte de la chlorophylle. Ce pigment, avec la phycocyanine et l&#8217;allophycocyanine, est organis&#233; en phycobilisomes, qui fonctionnent comme des antennes collectrices de lumi&#232;re. Les esp&#232;ces vivant en eaux profondes produisent g&#233;n&#233;ralement plus de phyco&#233;rythrine, leur donnant une apparence rouge fonc&#233;, tandis que celles vivant en eaux peu profondes en produisent moins et peuvent appara&#238;tre vertes.
La plupart des algues rouges sont multicellulaires et d&#233;pourvues de flagelles. Certaines vari&#233;t&#233;s, appel&#233;es commun&#233;ment algues marines, sont exploit&#233;es commercialement. Elles sont une source d&#8217;agar, un agent g&#233;lifiant cl&#233; pour les milieux de culture microbiologiques, ainsi que de carragh&#233;nanes, utilis&#233;es comme agents &#233;paississants et stabilisants dans l&#8217;industrie alimentaire. Certaines esp&#232;ces, comme celles du genre Porphyra, sont r&#233;colt&#233;es, s&#233;ch&#233;es et utilis&#233;es comme feuilles comestibles dans les sushis. Sur le plan morphologique, les algues rouges peuvent &#234;tre filamenteuses ou feuillues ; d&#8217;autres, notamment celles qui d&#233;posent du carbonate de calcium, pr&#233;sentent une apparence corallienne. Ces algues rouges corallig&#232;nes participent &#224; la formation et au renforcement des r&#233;cifs coralliens, les aidant &#224; r&#233;sister &#224; l&#8217;&#233;rosion provoqu&#233;e par les vagues.
Le genre Polysiphonia regroupe des algues rouges filamenteuses et ramifi&#233;es, pr&#233;sentes dans les milieux marins du monde entier. Ces organismes poussent principalement pr&#232;s des zones c&#244;ti&#232;res, s&#8217;attachant aux rochers, &#224; d&#8217;autres algues ou &#224; des surfaces artificielles comme les quais, murs de sout&#232;nement ou structures en b&#233;ton. Avec pr&#232;s de 200 esp&#232;ces reconnues, Polysiphonia pr&#233;sente un cycle reproductif complexe impliquant une alternance de g&#233;n&#233;rations. Au cours de ce cycle, des gam&#232;tes haplo&#239;des m&#226;les et femelles proviennent d&#8217;un organisme multicellulaire diplo&#239;de, puis &#233;voluent en organismes haplo&#239;des multicellulaires des deux sexes. Les algues m&#226;les lib&#232;rent des cellules reproductrices semblables &#224; des spermatozo&#239;des haplo&#239;des, qui fusionnent avec des structures reproductrices sp&#233;cialis&#233;es des algues femelles, formant des zygotes diplo&#239;des. Ces zygotes se d&#233;veloppent en organismes multicellulaires qui, apr&#232;s m&#233;iose, lib&#232;rent &#224; nouveau des gam&#232;tes m&#226;les et femelles, bouclant ainsi le cycle.
Outre les esp&#232;ces multicellulaires comme Polysiphonia, certaines algues rouges existent sous forme unicellulaire. Les membres de l&#8217;ordre des Cyanidiales, comprenant les genres Cyanidium, Cyanidioschyzon et Galdieria, vivent dans des environnements extr&#234;mes tels que les sources chaudes, acides et riches en m&#233;taux. Ces organismes tol&#232;rent des temp&#233;ratures comprises entre 30 &#176;C et 60 &#176;C et des pH aussi bas que 0,5 &#224; 4,0, des conditions hostiles pour la plupart des autres micro-organismes phototrophes, y compris les phototrophes anoxyg&#233;niques.
Les algues rouges unicellulaires pr&#233;sentent plusieurs caract&#233;ristiques distinctives. Par exemple, Cyanidioschyzon merolae poss&#232;de des cellules extr&#234;mement petites (1 &#224; 2 &#956;m de diam&#232;tre) et l&#8217;un des plus petits g&#233;nomes connus chez les eucaryotes phototrophes (environ 16,5 Mbp). Des &#233;tudes mol&#233;culaires sur Galdieria ont r&#233;v&#233;l&#233; qu&#8217;elle a acquis au moins 75 g&#232;nes par transfert horizontal &#224; partir de diverses sources procaryotes. Ces g&#232;nes conf&#232;rent des adaptations telles que la r&#233;sistance au stress salin, la protection contre la toxicit&#233; des m&#233;taux et des modifications renfor&#231;ant la membrane cytoplasmique, permettant la survie en conditions chaudes et acides. De plus, Galdieria a une capacit&#233; inhabituelle &#224; cro&#238;tre dans l&#8217;obscurit&#233; totale, gr&#226;ce &#224; des g&#232;nes acquis qui codent des syst&#232;mes de transport pour utiliser des compos&#233;s organiques comme sources d&#8217;&#233;nergie.
Bien que le transfert horizontal de g&#232;nes soit g&#233;n&#233;ralement observ&#233; entre organismes procaryotes, le cas de Galdieria illustre son r&#244;le important dans l&#8217;&#233;volution des g&#233;nomes microbiens, m&#234;me entre diff&#233;rents domaines phylog&#233;n&#233;tiques.

Principaux phylums d’algues

Les algues rouges, &#233;galement appel&#233;es rhodophytes, se trouvent principalement dans les milieux marins, bien que certaines esp&#232;ces vivent en ...

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red algae pigments, shapes, and uses

Red algae are phototrophic organisms found mostly in marine environments. Some species also live in freshwater or on land. They may be unicellular or multicellular, and some multicellular forms grow large enough to be seen easily.

These algae contain chlorophyll a, but their chloroplasts do not contain chlorophyll b. Instead, they use phycobiliproteins, which are light-harvesting pigments like those found in cyanobacteria. The red color seen in many species comes from phycoerythrin, an accessory pigment that hides the green color of chlorophyll. Phycocyanin and allophycocyanin also help capture light. These pigments are arranged in phycobilisomes, which act like antennae for light harvesting. Red algae from deeper water often make more phycoerythrin and appear darker red. Shallow-water species may have less of this pigment and can even look green.

Most red algae are multicellular and do not have flagella. Many seaweed species have commercial value. They are sources of agar, which is used to solidify microbiological culture media. They also provide carrageenans, which are used as thickening and stabilizing agents in food. Some red algae, such as members of the genus Porphyra, are harvested, dried, and eaten as sushi wraps.

Red algae can have different body forms. Some are filamentous, and others are leafy. Certain species deposit calcium carbonate and take on a coral-like look. These coralline red algae help form and strengthen coral reefs, where they add support against wave erosion. The genus Polysiphonia is a common example of filamentous, branched red algae found in marine habitats around the world. It often grows near shore and attaches to rocks, other algae, jetties, retaining walls, docks, and concrete surfaces.

Polysiphonia also shows a complex life cycle with alternation of generations. In this cycle, haploid male and female gametes come from a diploid multicellular organism and grow into haploid multicellular male and female individuals. The male algae release haploid sperm-like cells. These fuse with specialized reproductive structures on female algae to form diploid zygotes. The zygotes develop into multicellular organisms, and meiosis then produces male and female gametes again.

Not all red algae are multicellular. Some, including members of the order Cyanidiales such as Cyanidium, Cyanidioschyzon, and Galdieria, are unicellular and live in extreme hot, acidic, and metal-rich springs. They can survive temperatures from 30°C to 60°C and pH values as low as 0.5 to 4.0. Cyanidioschyzon merolae has very small cells, only 1 to 2 micrometers wide, and one of the smallest genomes known among phototrophic eukaryotes, at about 16.5 megabase pairs.

Studies of Galdieria show how gene transfer can shape survival. This alga has gained at least 75 genes from prokaryotic sources through horizontal gene transfer. These genes help with salt stress, metal toxicity, and membrane stability in harsh environments. Galdieria can also grow in complete darkness. That ability is linked to genes for transport systems that let it use organic compounds as energy sources. Its genome shows that horizontal gene transfer can be important even across different major groups of organisms.

Red Algae Pigments, Shapes, and Uses

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red algae

Red algae are phototrophic organisms found mostly in marine environments. Some species also live in freshwater or on land. They may be unicellular or multicellular, and some multicellular forms grow large enough to be seen easily. These algae contain chlorophyll a, but their chloroplasts do not contain chlorophyll b. Instead, they use phycobiliproteins, which are light-harvesting pigments like those found in cyanobacteria. The red color seen in many species comes from phycoerythrin, an...

green algae

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Alveolates: Ciliates, Dinoflagellates, Apicomplexans

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diversity of protists iii

Rhizaria: Pseudopods, Tests, and Skeletons

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diversity of protists iv

Amoebozoa: Movement and Life Cycles

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key terms and concepts

Explore red algae pigments, body forms, commercial uses, reef-building species, alternation of generations, and extreme-environment unicellular forms.

Red Algae Pigments, Shapes, and Uses | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Red Algae Pigments, Shapes, and Uses

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