Auxenochlorella
| Auxenochlorella | |
|---|---|
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Viridiplantae |
| Phylum: | Chlorophyta |
| Class: | Trebouxiophyceae |
| Order: | Chlorellales |
| Family: | Chlorellaceae |
| Genus: | Auxenochlorella |
| Species | |
| Synonyms | |
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Auxenochlorella protothecoides, formerly known as Chlorella protothecoides, is a facultative heterotrophic green alga in the class Trebouxiophyta known for its potential application in biofuel production. It was first characterized as a distinct algal species in 1965, and has since been regarded as a separate genus from Chlorella due its need for thiamine (not to be confused with thymine) for growth.Auxenochlorella has been found in a wide variety of environments from acidic volcanic soil in Italy to the sap of poplar trees in the forests of Germany. Its use in industrial processes has been studied, as the high lipid content of the alga during heterotrophic growth is promising for biodiesel; its use in wastewater treatment has been investigated, as well.
Auxenochlorella can be characterized by its trilaminar outer wall layer and lack of pyrenoid. A recent phylogenetic analysis has clarified its position with respect to related strains.
Auxenochlorella has potential in biofuel production, as it can accumulate high lipid content under heterotrophic conditions. The A. protothecoides genome has been sequenced and compared to two other species (C. variabilis and Coccomyxa subellipsoidea). It was found to have a smaller genome size that encodes fewer genes, fewer multi-copy genes, fewer unique genes, and fewer genome rearrangements than its close relatives. Furthermore, three genes were identified that enable the consumption of glucose and, thus, heterotrophic growth. These three Chlorella-specific hexose-proton symporter (HUP)-like genes, in addition to rapid pyruvate synthesis, fatty acid synthesis enzyme upregulation, and fatty acid degradation enzyme downregulation, contribute to the high lipid content.
The algae have also been shown to grow on plethora of media, including glycerol, glucose, and acetate. One study showed that the Auxenochlorella heterotrophically synthesized a maximum crude lipid content of 55.2% dry weight. Separate studies have confirmed that large amounts of lutein, a type of carotenoid that can be used as a drop-in fuel source, are also produced.
It should be noted that Auxenochlorella biofuel production poses similar efficiency problems as other algal species, as the pyrolysis and drying process are expensive and time- consuming. In addition, the biofuel studies were generally done with fed batch culture in order for the algae to maintain log phase growth and maximize yields, a process that may be expensive on a larger scale.
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