It was an unscheduled, almost impulsive, detour to plumb one of the deepest points in the Indian ocean. Geologist Bejugam Nagender Nath had spent four weeks with a team of scientists aboard a ship cruising the central Indian ocean, trying to predict how seabed mining in the future may change the marine ecosystem. On the way back, he proposed a change in the ship's course to an unexplored underwater canyon called the Chagos Trench.
There, using a winch, the scientists scooped up from a depth of nearly six kilometres a chunk of seabed sediment that resembled a giant slab of dark wet chocolate, dropped it into a sterile chamber, and began to examine it for signs of life.
Now, five years after their detour to the Chagos Trench, the scientists from the National Institute of Oceanography (NIO), Goa, have announced their discovery of the oldest known living fungi, buried and lying dormant, in those sediments for over 430,000 years.
When the NIO scientists put the fungi into flasks containing the right broth of nutrients, the organisms began to multiply. The fungi might provide insights into the unknown biological tricks that allow microbes to hibernate for long periods of time, serve as a peephole into the climate on earth in the remote past, and also bolster support for the idea that microbes may be found elsewhere in the solar system.
'A big question in biology is how long can life survive in extreme conditions,' says Chandralata Raghukumar, a marine biologist who was part of the team that isolated the fungi. 'And while these fungi are fascinating from the point of view of biology, we can't rule out commercial applications from such organisms.'
The NIO studies show that the fungi are ancient organisms that were deposited on the seabed and then got entombed under the accumulating sediments.
'This is an important discovery ' the fungi are nearly as old as Homo sapiens who appeared as a species less than a million years ago,' says David Karl, professor of oceanography at the University of Hawaii, who had himself isolated ancient bacteria from deep layers of ice on Antarctica five years ago. 'Any report of organisms from ancient environments, whether ice or sediments, is pot- entially important.'
Scientists have long suspected that microbes remain trapped beneath layers of ice or buried within seabed sediments, but interest in such organisms has intensified in recent years.
Over hundreds of thousands of years, as the thickness of the ice and the sediments grew over time, the organisms were buried deeper and deeper. Yet, a number of discoveries over the past decade have shown that some of these long-buried microbes ' bacteria and fungi ' remain viable. When pulled out of their 'graves' and placed in flasks with nutrients rich in glucose and amino acids, they multiply and produce colonies, visible to the naked eyes, on the walls of their flasks.
The long periods for which such ancient microbes remain viable have baffled scientists. Over the past four decades, researchers have isolated bacteria from 5,800-year-old sediments in the eastern Pacific ocean, from 8,000-year-old deposits of permafrost in Siberia, and from layers of ice below the Vostok Station on Antarctica, believed to be some 400,000 years old.
In 1995, biologists Raul Cano and Monica Borucki at the California Polytechnic State University surprised the scientific community by announcing that they had cultured and identified bacteria from inside an insect preserved for 25 million years in amber, the fossilised resin of ancient trees. The two biologists convincingly argued that the bacteria they had isolated was indeed an ancient organism and not merely a modern-day germ that had contaminated their experiments.
'Organisms that survive in such environments have major implications on evolution, microbial survival and ecology,' says Scott Rogers, a biologist at the Bowling Green State University in Ohio, US. He has collected samples of more than 500 fungi and 300 bacteria from the layers of ice in Greenland and on Antarctica. The age of the ice layers where Rogers found these organisms varies from less than 500 years to more than 420,000 years.
'Most previous studies on ancient microorganisms have focused on ice and not on seabed sediments,' says Chandralata, the NIO marine biologist who has been studying marine fungi at the NIO for the past two decades along with her husband Seshagiri Raghukumar.
Both were students pursuing doctorate degrees in biology in Madras during the 1970s when Raghukumar got an offer to work on a project to study fungi from the sea at the Institute for Polar and Marine Research in Bremerhaven, Germany. The couple spent five years there and joined the NIO in the 1980s and began to study marine fungi from the Arabian sea, Bay of Bengal and the Indian ocean.
The NIO team wasn't looking for ancient microbes when Nagender Nath decided to sail to the Chagos Trench. The cruise, sponsored by the Department of Ocean Development (DOD), aboard the A A Sidorenko, a chartered Russian ship, was intended to get data that might help predict the likely impacts of seabed mining on the underwater ecosystem.
India was the first country to acquire a piece of real estate on the seabed in the 1980s, and since then has been pursuing technologies to mine the seabed for metals such as cobalt, nickel, and copper. While scooping metals from the sea is not economically viable today, DOD is funding the development of relevant technologies and studies to determine how mining the seabed would affect the marine environment.
'I had been wanting to go to Chagos a long time, but it hadn't been possible on previous cruises. This time we weren't too far away, and we had time to spare,' says Nagender Nath, a veteran of more than 20 research trips into the Arabian Sea and Indian ocean over the past two decades. Last week, he set out out on another cruise ' this time to identify potential 'first-generation' seabed mining sites.
Nagender Nath was among a team of geologists specially recruited by the NIO in the 1980s to launch India's first deep-sea geological exploration programme. His interests have since veered to the connection between geology and biology.
The Chagos Trench from that perspective is interesting because of its depth and the age of its sediments. 'Seabed sediments and their contents can also tell us something about the past climate,' says Nagender Nath.
The climate can influence the abundance of organisms buried in seabed sediments. During an ice age, when much of the water is locked up in snow and glaciers, the abundance of large and small organisms in the ocean drops. And during warm periods, ocean productivity is raised.
The ice-age cycle may thus be represented by spikes and dips in the abundances of organisms. Geologists believe that seabed sediments can also help determine wind patterns and river flows in the past.
At the Chagos Trench, the NIO scientists used a 10-cm pipe to scoop up five metres of sediments and hauled it aboard the ship. The cylinder-shaped chunk of the retrieved sediment was cut to slices, each layer indicating a different age. 'The deeper the core, the older the sample,' says Chandralata.
Scientists have estimated that it takes about 1,000 years for one centimetre of sediment to deposit on the seabed. The NIO team found fungi that could be revived in the laboratory in a section corresponding to 3.7 metres beneath the seabed. The best-growing fungus was identified as an organism called Aspergillus sydowii, a common organism found in terrestrial soils even today.
The scientists had no explanation for the presence of the fungi buried under the seabed. 'Initially, the discovery puzzled us,' says Raghukumar. 'Why should these fungi abruptly appear deep under the sediments' If the fungi had seeped through the seabed down to the 3.7-metre depth, the abundance would be greater in the higher than in the lower layers. But there was no such pattern.'
| Echoes from the deep: Scientists on board AA Sidorenko collect samples from sea bottom
Raghukumar recalled having read research papers from the US and elsewhere on prehistoric bacteria preserved in ice and began to wonder whether these fungi might also be ancient organisms buried under sediments over time.
Fossils of other species present in the sediments helped the NIO team assign a date to the layers where the fungi were found ' at least 430,000 years old. The researchers have published these findings in the journal Deep Sea Research.
Buried in the sediments, the fungi are subjected to extreme pressures ' hundreds of times the normal atmospheric pressure ' and extreme cold (the temperature of the seabed is always about two degrees celsius).
Chandralata says the low temperature and high pressure may have played a role in keeping the organisms viable for such a long time. In experiments at the NIO, the scientists found that the fungal spores retrieved from the Chagos Trench continued to germinate at extreme pressures and low temperatures. This suggests that they had become used to the deep-sea environment.
The viability of the fungi despite spending hundreds of thousands of years in such a hostile environment is also expected to support for the decades-old concept propounded by astrobiologists that microorganisms may survive on comets or within patches of ice elsewhere in the solar system.
Rogers and other enthusiasts for research on ancient life say that the investigative techniques developed to study such organisms on earth may one day contribute to the search for life on extraterrestrial worlds, perhaps on Mars or on Jupiter's moon Europa, or on comets, also believed to contain ice.
The NIO scientists also plan to investigate the deep-sea fungi for their commercial potential. Chandralata wants to look for fungal enzymes that function in cold water. Such enzymes will find use in detergents that work efficiently in cleaning clothes, even in cold water.
The NIO has already filed a patent on a protease enzyme from another species of fungi retrieved earlier from another point in the Indian Ocean.
While the fungi isolated from the Chagos Trench is found on terrestrial soils, some of the ancient organisms entombed under the ice or seabed sediments may be entirely new organisms. And they may contain useful genes or proteins. 'I don't think that most of us even know how many discoveries are on the near and far horizon,' says Rogers.