Faculté des Sciences Tétouan ¦ Département de Biologie
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Ce PFE est réalisé par : Oulad Belayachi Laila
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Abstract
Microalgae are phytoplanktons that carry out photosynthesis; these microorganisms represent
a huge biodiversity in the world. Due to their eukaryotic organization, they consist of
organelles; include nuclei, mitochondria and chloroplasts, etc. These organelles contribute in
the metabolism by producing either protein, oils or sugar via many biological processes such
as photosynthesis and fatty acids biosynthesis. In order to use this rich biomass in
human/animal nutrition, cosmetics and biodiesel, many cultivation methods have been used,
from open cultivation systems like the open ponds to closed ones like photobioreactors. The
same thing with the special microalgae Haematococcus pluviaris which is capable of
producing a highly antioxidant molecule called astaxanthin. Its production required a strict
method starting with cultivation and ending with harvesting and extraction.
Key-words: Phytoplanktons, biodiesel, astaxanthin.
Résumé
Les microalgues sont des phytoplanctons qui pratiquent la photosynthèse; ces
microorganismes représentent une grande biodiversité dans le monde. Grâce à leur
organisation eucaryotique, ils sont constitués d’organites ; inclus le noyau, les mitochondries
et les chloroplastes, etc. Ces organites contribuent dans le métabolisme par la production soit
de protéines, de lipides, ou de sucre via plusieurs processus biologiques comme la
photosynthèse et la biosynthèse des acides gras. Afin d’utiliser cette riche biomasse en la
nutrition humaine/animale, les cosmétiques et le biodiesel, plusieurs méthodes de culture ont
été utilisées, de systèmes ouverts comme les bassins ouverts à des systèmes fermés comme les
photobioréacteurs. La même chose pour la spéciale microalgue Haematococcus pluviaris qui
est capable de produire une molécule très antioxydant appelé astaxanthin. Sa production
demande une stricte méthode qui commence avec la culture et se termine avec la récolte et
l’extraction.
Introduction
Microorganisms in general represent a large biodiversity in the world, from prokaryotic ones
such as bacteria, to eukaryotic ones such as microalgae.
Due to their simple morphology and physiology, bacteria are well studied microorganisms,
unlike microalgae which have complicated organelles and require even more research
(Sheehan et al., 1998).
However, Microalgae are one of the most ancient organisms living on earth and one of the
tiniest plants. They have survived some of earth’s harshest conditions for several billion years.
These unicellular species are capable of performing photosynthesis (converting light energy to
chemical energy), in order to produce not only more than 75% of the atmospheric oxygen, but
also carbohydrates, protein and lipids from 30 to 100 times faster than land plants (Kamyab,
2012 ; Spolaore et al., 2006). That is why they need to be highlighted and studied despite the
high cost of their production (Sheehan et al., 1998).
In order to understand the principal characteristics of microalgae, their biochemical
proprieties and their importance, this study will discuss:
-The microalgal biodiversity by highlighting the main classes and the differences
between them based on pigmentation, life cycle and cellular structure.
-The microalgal morphology by detailing the principal organelles present in a
microalga.
-The microalgal metabolism from photosynthesis process to starch, fatty acids and
lipids biosynthesis.
-The cultivation methods and systems such as open ponds (open system) and
photobioreactors (closed system).
-The use of microalgae in a variety of industries and fields like nutrition, cosmetics
and even in biodiesel production by transesterification.
Moreover, this study will take as an example Haematococcus pluviaris. A special green
microalga that turns red during harsh conditions and can produce a huge proportion of highly
antioxidant molecule which is astaxanthin (a xanthophyll carotenoid); this molecule has an
exceptional range of benefits such as maintaining the immune response etc. (Chekanov et
al.,2014 ; Kidd, 2011).
General conclusion
In general, microalgae have shown a lot of benefits on so many levels. These microorganisms
have a promising future in the biotechnical industry, from producing carbohydrates, proteins
and natural oils, to producing biodiesel via transesterification. This last process can help
saving the environment by abandoning the petroleum fuels and depending even more on algal
biomass as natural resource. Unfortunately, the high cost of producing this biodiesel prevents
it from becoming economically competitive, which is why it is necessary for future research
to find another sheep method to produce it.
As for the red pigment astaxanthin, the Chlorophyte Haematococcus pluvialis accumulates
large quantities of it as a stock; this pigment has demonstrates several positive effects of
human health, so as a result, it is acceptable to say that this antioxidant molecule is also a very
promising product in many ways.
In order to exploit microalgae in the best way possible, researches must look for better
methods either to cultivate them or to extract their biomass without wasting any of its
amounts.