Washington, Nov 15 : Scientists have discovered an unusual microorganism in the sea that plays an important role in ocean ecology, and may force them to rethink their understanding of how carbon and nitrogen cycle through ocean ecosystems.
A research team led by Jonathan Zehr, a marine scientist at the University of California, Santa Cruz, characterized the new microbe by analyzing its genetic material, even though researchers have not been able to grow it in the laboratory.
Zehr said that the newly described organism seems to be an atypical member of the cyanobacteria, a group of photosynthetic bacteria formerly known as blue-green algae.
"This research has revealed a big surprise about the microbiology of the oceans, and the complex integration of the ocean's nitrogen and carbon cycles," said Philip Taylor, section head in the National Science Foundation (NSF)'s Division of Ocean Sciences, which funded the work.
"The fact that nitrogen fixation in these abundant unicells is decoupled from photosynthesis is intriguing," said Taylor. "This unique adaptation brings up questions about the role of these abundant microbes in the ocean," he added.
Unlike all other known free-living cyanobacteria, this one lacks some of the genes needed to carry out photosynthesis, the process by which plants use light energy to make sugars out of carbon dioxide and water.
But, the mysterious microbe can do something very important.
It provides natural fertilizer to the oceans by "fixing" nitrogen from the atmosphere into a form useable by other organisms.
"For it to have such an unusual metabolism is very exciting," Zehr said. "We're trying to understand how something like this can live and grow with so many missing parts," he added.
The new microbe is one of the most abundant nitrogen fixers in many parts of the ocean, according to Zehr.
New DNA sequencing technology enabled rapid sequencing of the organism's genome.
"I had begun to suspect that there was something missing in this organism's genome, and the genome sequencing confirmed that," said Zehr.
The results showed that it is missing the entire set of genes needed for photosystem II and carbon fixation, essential parts of the molecular machinery that carries out photosynthesis in plants and cyanobacteria.
"That has multiple implications," Zehr said. "It must have a 'lifestyle' that's very different from other cyanobacteria. Ecologically, it's important to understand its role in the ecosystem and how it affects the balance of carbon and nitrogen in the ocean," he added.
Efforts are currently underway to map the microbe's presence in the oceans and determine its global abundance.