On Thursday December 2nd 2010, NASA announced the unusual behaviour of a strain of Bacteria GFAJ-1 belonging to the Halomonadaceae family living in the Monolake near the California Yosemite National Park. This Proteobacteria incorporates the toxic Arsenic molecules in their DNA in the place of Phosphate molecules. This amazing discovery shows that an organism can use even a highly toxic chemical for its survival. This is really amazing. The adaptability of nature can change the conventional concepts since necessity can change a life pattern.
From Lake to Lab
The work of Felisa Wolfe-Simon and colleagues revealed that, the GFAJ-1 bacteria can take arsenic and incorporate it into their cells for synthetic metabolism. They grew the bacteria in Petri dishes in which the phosphate salt was gradually replaced by arsenic salt until the bacteria grown without phosphate. The bacteria utilized arsenic to synthesize the building blocks of cells such as DNA, Proteins and Lipids. By using Radiotracers, the researchers found that the bacteria can incorporate the arsenic in various bio molecules including DNA. They found higher arsenic and lower phosphorus content in purified genomic DNA of bacteria grown in arsenate compared to control cells.
Mono lake of California
A substitute from Periodic table
The implications of this discovery are enormous to our understanding of life itself. This is really interesting. All life forms are composed of six elements- Carbon, Hydrogen, Nitrogen, Oxygen, Sulphur and Phosphorous. DNA of all organisms is made up of Nitrogen bases, Pentose sugar and Phosphate group. The GFAJ-1 bacteria are living in a highly toxic environment rich in arsenic (200 uM). So they utilized the arsenic in the absence of phosphorous for their survival.
The phosphorus atom in the DNA is bonded to four oxygen atoms. Phosphorus is a Group 15 element that shares chemical properties with nitrogen which is one period above it on the periodic table. Arsenic lies one period below it. It is this chemical similarity to phosphorus that allows arsenic to form a similar compound , called Arsenate.
Phosphate and Arsanate
Something about Proteobacteria
Proteobacteria is one of the major groups of bacteria and includes the common Escherichia coli, Salmonella, Vibrio, Helicobacter etc. Most of these are pathogenic forms while others are free living including the Nitrogen fixers. All Proteobacteria are Gram negative strains with an outer membrane composed of lipopolysaccharides. Some forms are motile having a single flagellum while others move through bacterial gliding mechanism. Most members are facultative or obligatory anaerobic, chemotropic or heterotrophic forms. Some bacteria like Purple bacteria are photosynthetic.
Class : Gamma Proteobacteria
Genera: Carnimonas , Chromohalobacter , Cobetia , Halomonas , Halotalia , Salinomonas , Zymobacter.
For more information see www.sciencemag.org
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