A single litre of sea water drawn from the deep ocean contained more than 20,000 different types of bacteria, when just 1,000 to 3,000 were expected.

"Microbiologists have formally described 5,000 microbial 'species'," says Mitchell Sogin, director of the Marine Biological Laboratory's (MBL) Josephine Bay Paul Centre for Comparative and Molecular Biology and Evolution, located in Woods Hole, Massachusetts.

"This study shows we have barely scratched the surface," Sogin said in a statement.

Water samples were taken at depths of 550 to 4,100 metres at eight Atlantic Ocean sites between Greenland and Ireland, as well as Pacific sites that included a hydrothermal vent on an underwater volcano 480 km off the coast of the U.S. state of Oregon.

The vast majority of microbes are previously unknown, low-abundance organisms theorised to play an important role in the marine environment, Sogin said.

Although not widely recognised, microbes have shaped life here on Earth, says Julie Huber, Sogin's colleague at the MBL. They play important roles in the global carbon and nitrogen cycles both in the oceans and on the surface of the planet, Sogin told IPS.

"The marine microbial biosphere is the largest habitat on Earth, and the sub-seafloor is the least explored part," she said.

More is known about the surface of Mars than the deep oceans, in large part because it is so difficult to "see" what is going on at the bottom of the ocean, most of which lies in utter darkness under the enormous pressures of 2,000 or more metres of water.

This new discovery of microbial abundance required the use of a Canadian deep sea underwater robot vehicle called ROPOS that can dive to 6,000 metres to obtain samples around an active underwater volcano in the Pacific. In the Atlantic, a team lead by researchers from the Netherlands used an ingenious system of bottles that opened and closed at precise depths, Huber said.

The main technical breakthrough, however, involved using a revolutionary new DNA technique, called "454 tag sequencing," that requires only small snippets of genetic code to identify an organism.

"Peering through a laboratory microscope into a drop of seawater is like looking at the stars on a clear night," says marine microbiologist Victor Gallardo of Chile, vice chair of the Census of Marine Life.

This study is part of the International Census of Marine Microbes (ICoMM), a project of the Census of Marine Life, a 10-year global initiative started in the year 2000 that now involves more than 1,700 researchers in over 70 countries in efforts to assess and explain the diversity, distribution and abundance of life in the oceans -- past, present, and future.

"The '454 tag sequencing' strategy increases resolution like the Hubble Telescope. We can see marine microbial diversity to which we were blind before. These rare, ancient organisms are likely to prove a key part of nature's history and strategy," said Gallardo in a statement.

To place the challenges of studying deep sea life in context, it was only last week that researchers announced in the science journal Nature the first cultivation of a bacteria from deep-sea hydrothermal vents in the lab, even though such vents were discovered more than 25 years ago.

That is mainly because such bacteria grow under unique conditions where waters are very acidic or even poisonous, and temperatures are 100 degrees C or more.

And this expedition found tiny creatures that were stranger still.

"We found some very unusual DNA that was different from anything ever seen before," said Huber.

There were small numbers of very ancient bacteria from millions of years ago that may exist nowhere else now and could be useful in understanding how life in the oceans evolved.

"They (the microbes) were the only kinds of life on Earth for approximately 80 percent of the planet's history," said Sogin.

These very old microorganisms have survived a great deal of change and may have something to teach as we experience global climate change, he said. "Exploration of this newly discovered 'rare biosphere' could become a major field of marine biology," the scientist added.

Another mysterious finding was thousands of different types of bacteria that were only present in small numbers.

"This may mean at one time, conditions in the deep ocean were very, very different," Huber speculates.

Or perhaps, despite their low numbers, they play an important function such as producing some essential compound.

Another hypothesis is that these are a kind of genetic backup system so that if species are wiped out elsewhere, the deep-ocean remnants could re-populate those areas.

"That could make the oceans more genetically resilient," she said.

It also means many more potentially useful microbes for study. For example, a bacteria from deep sea vents is being used to make an enzyme that plays a key role in the process of turning corn into ethanol, said Antje Boetius of the Max Planck Institute of Marine Microbiology in Bremen, Germany.

The PCR test, the first and most basic tool for DNA analysis, is based on bacteria also found at deep sea vents, Boetius told IPS.

Marine bacteria can live under extraordinary conditions and do amazing things such as taking carbon dioxide out the water. Although they are the smallest living things in existence, microbes make up 33 percent of the total living biomass on the earth, she said.

Deep sea exploration is too expensive to extensively sample the oceans, but ICoMM is hoping to receive 500 ocean water samples collected in past by other researchers from around the world.

"We can't understand the oceans without knowing how marine bacterial communities function," says Huber.

Source: IPS - Inter Press Service News Agency