Algae, a vast diversity…
Algae are photosynthetic non-vascularized organisms with a reproductive cycle that inevitably requires water.
The morphologies of algae are extremely diverse. They can be either unicellular or multicellular. Phytoplankton are non-fixed, unicellular, microalgae species, which float or swim in open water. They are divided into several groups, according to their colour and structure (eg: Diatoms, Flagellates, Chlorophyceae, etc.).
Macroalgae or seaweed are visible to the naked eye and are most often attached to bedrock. Like microalgae, they vary in colour due to the presence of particular pigments which more or less mask the presence of chlorophyll, and which allow them to be classified into different categories:
- Green algae such as Ulva and Caulerpa;
- Red algae such as Porphyra and Palmaria;
- Brown algae such as Fucus and Laminaria (1).
At present, scientists estimate the number of algal species somewhere between 200,000 and several million. Amongst these, only 30,000 species have been studied extensively (2).
However, since difficulties arise for identifying them … there is a solution: barcoding!
For a number of reasons, biologists are often confronted with taxonomic identification problems: complex morphological characteristics, imprecise identification keys, increasing scarcity in the number of expert taxonomists for a given group, cryptic diversity (not based on morphological characters), or even the absence of morphological characters when confronted to processed material (major food issue).
Algae are no exception: their identification is not always easy due, among other reasons, to their morphology, to their phenotypic plasticity and to the alternation of generations that can be heteromorphic (3). In addition, since algae are often used after they have been transformed (dried and / or crushed algae), it becomes impossible to identify them on the sole basis of morphological characters. However, an important issue for the traceability and quality of products lies in the capability of producers and manufacturers to precisely identify the algal species.
To complete this taxonomic expertise, molecular biology offers a method for identifying species through DNA fragment sequencing: barcoding.
From a sample of powder or flakes, the DNA contained in the sample can be extracted and PCR amplification can be carried out using markers targeting genes used for the barcoding of micro- and macro-algae (red, green and brown). For example, in addition to the COI marker (encoding a subunit of the enzyme cytochrome oxidase, involved in the chain of biochemical reactions of respiration), other genes are now used as bar codes, such as such as the chloroplastic rbcL gene, the nuclear ITS genes (Internal Transcribe Spacer), or the tufA gene located in the plastid of algae. The amplified PCR products are then sequenced and the sequence data analysed and compared to reference databases. It thus becomes possible to establish the identity of the algae or seaweed present in the initial sample.
The barcoding technique proves to be a significant tool for identifying algae that are often used in powder or flake form as a raw material base composing various products. Indeed, it is essential to associate the appropriate species of algae to a given application, since each has specific properties and requirements. This technique has been proposed by various laboratories including Vegenov.
References:
(1) Classification of algae: red algae, blue algae… – Claire König – 03-09-2005 – Futura Planète
(2) Algae, Eldorado of tomorrow – DENIS SERGENT – 01-28-2013 – LA CROIX
(3) Saunders, G.W. (2005). Applying DNA barcoding to red macroalgae: a preliminary appraisal holds promise for future applications. Philos. Trans. R. Soc. B Biol. Sci. 360, 1879–1888.
This post was written jointly by:
- Céline Hamon, R&D manager in molecular biology at Vegenov
- Charlotte Roby, molecular biology engineer at Vegenov
- Juliette Clément, intelligence and documentary research officer at Vegenov
