Chlamydomonas Reinhardtii – Wikipedia

Chlamydomonas reinhardtii is a kind of green algae, used as a model in vegetable biology. Its genetic, structural (unicellular) and growth characteristics (cultivation on Petri box or in liquid environment) sometimes earn the nickname of “Green yeast” , by analogy with yeast Saccharomyces cerevisiae , model organism of non -photosynthetic unicellular eukaryotes.

This mobile alga has been used as a model since the 1960s to, in particular, study the functioning of plant flagelles, photosynthesis and certain genomic peculiarities that it shares with animals. It is with this organization that the biogenesis of the flagelles has been studied and that the presence of DNA in the chloroplasts was discovered.
The decryption of his genome began in 2001 and was published six years later by the journal Science (Oct 2007). 120 million base pairs form around 15,000 genes. These include a mixture of animal and plant genes: 35% of these genes are common to this species, with flower plants and humans, 10% are typically animals, including those coding enzymes (nucleotides cyclases or those synthesizing selenoproteins in certain animal lines including vertebrates) ^{[ 2 ]} , which is a lot for a unicellular seaweed. Complete decryption has associated a hundred researchers mobilized by the Genome Institute (JGI) joint of the American Department of Energy (D0E). Olivier Vallon (CNRS) coordinated the annotation of the genome (functional description of the genes), which could be useful to better understand its operation, or exploit it for genetic engineering.

Telomeres are generally made up of repetitions of a TTTTAGGGGS sequence. They are preceded by sub-trélomeres (in) , constituted (out of 31 of the 34 ends of chromosomes) not of transposons but of specific repetitive sequences called “sultan” ( Subtelomeric Long Tandem Repeat ), about 850 nucleotides, repeating itself from 2 to 46 times per end ^{[ 3 ]} .

Carbon dioxide deficiency behavior [ modifier | Modifier and code ]

A 2012, L’PLAY PLAY THE OLGA BIFUREN-classes ^{[ 4 ]} , of the German University of Bielefeld, in Rhinenania-du-Nord-Westphalia, observed that placed in an extreme environment poor in carbon dioxide, a necessary element in the photosynthesis process, the green micro-algae secretes an enzyme that allows it to digest the cellulose of other plants. Digestion takes place outside the cell, and sugars are then transported in the cell. This is the first time that we have observed in a unicellular chlorophyllian organism the ability to produce organic matter by digestion, therefore other than by photosynthesis.

Since then, we know that unicellular microorganisms Mixotrophes, as mesodinium chamaeleon are capable of digesting green microalgae, or keeping red microalgae and their photosynthetical pigments within them in order to feed both digital nutrients and enjoy the photosynthesis.

Reproduction [ modifier | Modifier and code ]

Schematic representation of a longitudinal cut of Chlamydomonas reinhardtii .

Under favorable conditions, with nutrients like nitrogen, Chlamydomonas reinhardtii grows and multiplies asexually, whether lit or not. But during a nitrogen deficiency, and with light, it differs into gametes by dividing itself into a mixture. Light seems to act indirectly, by photosynthesis to have the energy to differentiate itself, and is not necessary for the merger of gametes afterwards. However, the addition of nitrogen to gametes causes the dedifferentiation of gametes to vegetative cells. The two types of gametes are apparently identical, and are called MT (+) and MT (-). Their fusion forms a stable non -flagelled diploid zygote that can remain sleeping while waiting for more favorable conditions, having a higher cell and nuclear size as well as more DNA per nucleus and a larger number of chromosomes. It also has a thicker wall. We are talking about mature zygote. When the environment is more favorable to the development of the algae, the zygote undergoes a meiosis and releases 4 or 8 haploid cells ^{[ 5 ] , [ 6 ]} .

Production of anti -cancer molecules [ modifier | Modifier and code ]

In 2013, Professor Tran team ^{[ 7 ]} in San Diego managed to transfer cells Chlamydomonas reinhardtii With a vector containing an immunotoxin anticancer. This vector is made up of:

• The variable part (heavy and light) of an anti -CD22 antibody (tumor antigen),
• Domains 2 and 3 of exotoxin has P.aeruginosa (Eukaryotal translation inhibitor by ribosylation of the EEF2 elongation factor),
• The constant domains CH2, CH3 of immunoglobulin 1 (make it possible to increase efficiency by homodimerization).

This immunotoxin is specifically attached to CD22 tumor antigens and inhibits the proliferation of cancer cells by action of exotoxin domains.

Biofuels production [ modifier | Modifier and code ]

Chlamydomonas reinhardtii is an emerging model for the production of biofuels. Indeed, its genome can easily be modified (Mirna, Crispr-Cas9, Transfection) which improves culture strains on several aspects:

• Improved robustness and growth by increasing photosynthetic efficiency by modifying the chloroplastic genome,
• Improvement of the production of biodiesel (from the transesterification of lipids) by increasing content in triacylglycérol in an nitrogen defined environment,
• Improvement of dihydrogen production in sulfur defined medium in order to reduce the inhibition of hydrogenase by oxygen.

It is therefore possible to genetically modify the strains of Chlamydomonas reinhardtii and/or produce them in various culture environments depending on what we seek to obtain. ^{[ 8 ]}