Friday, June 8, 2012

For the First time, genome of a polar alga, Coccomyxa subellipsoidea, sequenced fully.

Life is diverse and life exists in every part of the earth including the most extreme habitats. One such extreme habitat is the polar regions. There is poor understanding of the adaptive mechanisms used by polar organisms to function under extreme cold conditions.  More than 30 psychrophylic microbial genomes have been fully sequenced and these  Psychrophilic prokaryotes were found to possess various adaptive strategies for survival in cold environments, including cold-induced desaturation of fatty acids in membrane lipids, protective mechanisms against increased amounts of solubilized oxygen and ROS, synthesis of antifreeze lipoproteins and glycoproteins, and global change in amino acid composition of encoded proteins to decrease protein structural rigidity.

For the first time  the genome of  a polar eukaryotic  unicellular green alga  Coccomyxa subellipsoidea (C169) has  been sequenced by  a team of  Researchers from  Mediterranean Institute of Microbiology (France), University of Nebraska (USA)  DOE Joint Genome Institute (USA), University of Rostock (Germany), Hiroshima University (Japan) and Georgia Tech Center for Bioinformatics and Computational Genomics (USA).

Analysis of the 48.8 MB genome of this alga (for comparison (approximate ): Human genome size-3000 mb, E.coli genome size 4.5 MB, Rice genome size 370 MB) revealed that like the psychrophylic  microbes sequenced, this eukaryotic alga is also possessing special features
which can protect the organism from cold stress. Compared to  its relatives Chlorella variabilis and Chlamydomonas reinhardtii, the following protein families are  over represented:  proteins involved in lipid metabolism, transporters, cellulose synthases and short alcohol dehydrogenases.  Four over-represented protein families correspond to important steps in lipid metabolism. They include putative type-I fatty acid (FA) synthases, FA elongases, FA ligases and type 3 lipases. In addition, genes coding for the enzyme FA desaturase proteins have been identified. This enzyme is absent in other green algae. These proteins are suggested to be  involved in adaptive processes that allowed C-169 to survive in the Antarctic environment. These proteins are involved in  modification of the FA composition (polyunsaturated and branched FA) of membrane lipids to maintain membrane fluidity at low temperature  and production of antifreeze lipoproteins. C-169 encodes specific dioxygenase (DOPA-dioxygenase) and FA desaturases that use dioxygen as a substrate and can contribute to providing a higher level of protection of the metabolism against ROS.  In contrast to psychrophilic organisms that live in permanent cold environments, the C-169 is suggested to  live in Antarctic soils, which withstand wide fluctuations in temperature (typically from -50°C to +25°C).  This type of a model will be interesting to study because unlike psychrophilic organisms, they can provide valuable information about cold adaptation to organisms living in normal climatic conditions.

To know more about cold adaptations  read this review:
Molecular adaptations to psychrophily: the impact of ‘omic’ technologies

To read the original paper on Sequencing  Coccomyxa subellipsoidea (C169) click here

Print This Post


Post a Comment