Fungus from a deep-sea sediment core that is hundreds of thousands of years old can grow when placed in culture, scientists have discovered.
The fungi (blue streak) were isolated from deep sea sediments
Indian researchers say the fungi come from sediments that are between 180,000 and 430,000 years old.
The finding adds to growing evidence for the impressive survival capabilities of many microorganisms.
They are the oldest known fungi that will grow on a nutrient medium, the scientists say in Deep Sea Research I.
The core was drilled from a depth of 5,904m in the Indian Ocean's Chagos Trench.
Like other ocean trenches, it is oriented parallel to a volcanic arc and is one of the deepest regions of the Indian Ocean.
On board their research vessel, Dr Chandralata Raghukumar and colleagues from the National Institute of Oceanography in Goa, India, and the Indian Institute of Chemical Technology in Hyderabad carefully deposited 5cm-long portions of the core into plastic bags which they then sealed to avoid contamination with present-day microbes.
The scientists then attempted to isolate bacteria and fungi from the middle of the 5cm-long "subsamples", because this region had not been in contact with the pipe used to extract the core - and therefore any modern microorganisms on it.
Diluted malt extract agar was used as a nutrient medium to grow the fungus on. The team was able to culture fungi from six out of 22 subsections of the core.
At core depths of between 15 and 50cm, the scientists found fungus of a type that does not produce spores.
At a depth of 160cm (corresponding to an age of 180,000 years ago) they found high densities of a type of spore-producing fungus known as Aspergillus sydowii.
Considerable densities of this fungus were also found at depths of 280-370cm, corresponding to an age between 180,000 and 430,000 years ago.
The researchers think the microbes may be blown off the land into the sea. They then sink to the sea floor and are covered in deep-sea ocean sediments.
The oldest microorganisms found alive are thought to be bacteria isolated from 25-40-million-year-old bees trapped in amber.
In 2000, US researchers claimed to have found bacteria that had remained in suspended animation for 250 million years in salt crystals. But the claim was disputed almost as soon as it was made.
Microbiologist Dr Scott Rogers, of Bowling Green State University in Ohio, US, was unsurprised by the study, saying his own team had obtained similar dates for ancient fungal organisms they had recovered in ice.
Viable and perhaps actively growing microorganisms are also thought to survive in the depths of Lake Vostok in Antarctica. If so, they may have been isolated from outside communities of microorganisms for up to one million years.
Studying the distributions and numbers of fungal organisms in cores could tell scientists about past climatic conditions on Earth, say the authors of the study.