Genome analysis of marine microbe reveals a metabolic minimalist

February 22nd, 2010 - 5:08 pm ICT by ANI  

Washington, Feb 22 (ANI): The genome analysis of an unusual marine microbe has revealed a metabolic minimalist, as it has have ditched several major metabolic pathways, leaving it with a remarkably reduced set of genes.

This metabolic minimalist is a specialist uniquely suited to performing one very important function: taking nitrogen gas from the atmosphere and “fixing” it into a form that makes this essential nutrient available to other organisms.

Nitrogen fixation fertilizes the oceans, controlling overall biological productivity and thereby affecting how much carbon dioxide the oceans absorb from the atmosphere.

Jonathan Zehr, the marine microbiologist who discovered the microbe, said it has stubbornly resisted efforts to grow it in the laboratory, but that hasn’t stopped his team from determining the complete DNA sequence of its genome.

Genome analysis enabled the researchers to reconstruct the organism’s unusual metabolic lifestyle.

Zehr, a professor of ocean sciences at the University of California, Santa Cruz, characterized the microbe as an atypical member of the cyanobacteria, a group of photosynthetic bacteria formerly known as blue-green algae.

Still lacking a formal taxonomic classification, it is known only as UCYN-A.

First detected in the open ocean near Hawaii in 1998, it is now known to be periodically abundant in tropical and subtropical waters throughout the world.

“Biogeochemists have never been able to balance the nitrogen budget of the oceans - there seems to be more nitrogen produced than we can account for from known organisms. So, this organism may be an important part of the overall nitrogen budget,” Zehr said.

The researchers applied new genome sequencing and assembly techniques to produce the complete genome sequence from natural samples of DNA.

Because UCYN-A cannot be cultured, researchers used a cell-sorting technique called flow cytometry to obtain concentrated samples of the microbe from ocean water, and then extracted DNA from the cells for sequencing.

Although UCYN-A must depend on other organisms for key nutrients, the researchers have found no evidence that it lives in a close symbiotic association with another microorganism.

Zehr said the failure to find another organism closely associated with it suggests two possibilities.

“It might live in a cryptic association that’s very hard to sample because it’s fragile and just falls apart, or it may respond to blooms of other phytoplankton and live in the soup of nutrients excreted by other organisms,” he said.

“Nitrogen fixation takes a lot of energy, but this thing has figured out how to fix nitrogen without the normal pathways used to fuel it in other organisms. It presents a real evolutionary and ecological paradox,” Zehr said. (ANI)

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