University of Queensland researchers have discovered novel miniature organisms which call into question the minimum size for life as we know it on Earth.
At 20 to 150 nanometres (billionths of a metre) in length, the organisms, which they call nanobes, are much smaller than the smallest certified terrestrial bacteria ever found on the planet.
Researchers discovered the living colonies of organisms in ancient sandstones retrieved from an oil drilling site 3-5km below the Australian seabed. The finding has been reported in a recent issue of American Mineralogist.
The researchers behind the investigation are senior research fellow Dr Philippa Uwins and senior research officer Richard Webb of the University's Centre for Microscopy and Microanalysis (CMM), and PhD student Anthony Taylor of the CMM and Microbiology and Parasitology Department.
They believe they may be the only research group in the world with actively growing nano-organisms.
While studying sandstone samples from exploration wells several years ago, Dr Uwins discovered strange filaments on the rocks.
"They were very small - in the nano range, but we didn't know what they were," Dr Uwins said.
In unfunded research, and exercising their scientific curiosity, they performed numerous tests using state-of-the art ultra high-resolution scanning electron microscopy, transmission electron microscopy, X-ray spectroscopy and DNA staining.
The Lilliputian organisms were in the same size range but distinctly different from controversial fossil nanobacteria reported by NASA scientists in a Martian meteorite in 1996 and by other scientists in various rock types on Earth.
Testing by the three Australian researchers has shown that the nanobes fulfil many criteria to qualify as biological life.
Their colonies grew spontaneously, they contained genetic material (DNA) and their chemical and biological structures were consistent with life. For example, they were composed of biological materials such as carbon, oxygen and nitrogen, and they were membrane-bound structures surrounding a possible cytoplasm and nuclear area.
In true scientific fashion, the scientists tried to disprove themselves by seeing if there could be another, plausible and non-biological explanation for the nanobes.
They discounted many non-biological materials such as crystalline minerals, carbonates, fullerenes, carbon nano-tubes and non-living polymers and concluded it was difficult to propose any known non-biological materials which could account for the observed structures.
Funding - if only at a shoestring level - was required to advance the project to the next level of investigation.
In December, the project received $19,000 Australian Research Council small grant support for further molecular and structural analyses to determine whether the organisms were related to bacteria or fungi, or belonged to a different evolutionary tree altogether.
"We will be the first group to perform DNA sequencing on a new life form with important and significant implications in many areas of research including molecular and cell biology, earth planetary sciences, environmental microbiology, medical microbiology, biotechnology, chemical engineering and many others," Dr Uwins said.
"If it is proven beyond doubt scientifically that such small organisms exist, it will be a major contribution to the controversial debate concerning extra-terrestrial life and the origin of life on Earth and other planets."
The debate was triggered in 1996 when NASA scientists in Houston reported the existence of fossil nano-organisms in a 4.5 billion-year-old, potato-sized Martian meteorite which crashed to Earth in Antarctica about 13,000 years ago.
They suggested that the meteorite, known as ALH84001, showed evidence of extra-terrestrial ancient life on Mars. The egg-shaped fossilised objects observed in the Mars meteorite were 20 to 100 nanometres long.
The announcement caused U.S. Vice-President Albert Gore and then House Speaker Newt Gingrich to agree on the need for more government spending and put Mars exploration on the front burner. One of the goals of the Mars exploration program now is to determine whether life started on Mars early in its history.
Critics of the NASA discovery argued that such nano life forms were too small to exist, because they had insufficient volume to contain the enzymatic and genetic material essential for life. They argued that the small size would not allow the supposed nanobacteria to contain RNA and a cell wall.
The same criticisms were levelled at a number of scientists, including geologist Dr Robert Folk of the University of Texas who in 1993 reported that they could see the fossilised forms of ultrasmall microbes in many rocks and minerals found on Earth.
Dr Folk argued that nanobacteria may have escaped biologists' notice because they eluded the conventional tools used to study bacteria.
He said that 200 nanometres was both the smallest size visible with an optical microscope, and the mesh size of the filters commonly used by microbiologists to strain out bacteria from liquids.
It became standard microbiological thought, he said, that because no bacteria smaller than 200 nanometres were seen, that none existed. The smallest known bacteria to date are mycoplasma, minute bacteria which cause a common form of pneumonia, and which can be as small as 200 nanometres.
Since their announcement, NASA scientists have searched for living nanobacteria on Earth.
Dr Uwins said until now, there have been no living representatives for the Martian nano-organisms or other fossil nanobacteria described on Earth in various rock types.
"Therefore it has been hard to convince the scientific community that the fossil Martian nanostructures could be remnant life forms," she said.
Dr Uwins said factors that had made a big difference to the University of Queensland investigations had been the multi-disciplinary nature of the Centre for Microscopy and Microanalysis, and access to the $750,000 ultra high resolution Jeol 890 scanning electron microscope. The instrument is capable of one million times resolution, and is one of only a handful of such microscopes in the world.
She said while the researchers did not yet have conclusive evidence for reproduction and metabolism in nanobes, and while they had not determined their evolutionary development, their evidence strongly suggested the existence of nanobes as biological organisms.