The breathless BBC headline read “Do Nanobacteria Rule the Earth and Mars?” But this scoop was in 1999. Did we actually discover evidence for extraterrestrial life ten years ago?
Nanobacteria — controversial calcium carbonate crystals with a cellular appearance that some consider nanometer-size bacteria — were once hailed as possibly “the most common form of life on Earth.” There was speculation that “they might also be living on Mars.”
In 1996, a group of scientists led by David McKay of NASA’s Johnson Space Center published a paper speculating the existence of nanobacterial trace fossils on Martian meteorite ALH84001. If these structures were indeed left behind by nanobacteria and if nanobacteria are true organisms, their findings would imply the existence of life on Mars at one point in the planet’s history.
Nanobacteria, much smaller at <200 nanometers than the tiny “Whos” in Dr. Seuss’ “Whoville,” were long considered to be the smallest self-replicating organisms ever detected. But are they in fact organisms?
Where better to turn than SETI, the Search for Extraterrestrial Intelligence, to confirm the possible existence of organisms of extraterrestrial origin? SETI seeks evidence of life in the universe by looking for some signature of its technology. The SETI Institute is known for large radio telescopes pointing well past Mars to the far reaches of the known universe searching for intelligent life. SETI scientists not only scan the margins of the heavens for signs of life, they also probe the limits of life right here on Earth. This includes nanoscale organisms.
h+ Magazine contacted SETI microbe expert Dr. Rocco Mancinelli at one of the SETI Carl Sagan Center’s newest on-site laboratories to ask about nanobacteria. Dr. Mancinelli is an expert in halophiles — salt-loving bacteria — and has conducted tests showing that some halophiles actually can withstand the extreme cold, vacuum, and zero gravity of space.
“Recent evidence suggests a role for nanobacteria in a growing number of human diseases, including renal stone formation, cardiovascular diseases, and cancer,” says Dr. Mancinelli. “This large body of research studies promotes the view that nanobacteria are not only alive but that they are associated with disease pathogenesis. However, it is still unclear whether they represent novel life forms, overlooked nanometer-size bacteria, or some other primitive self-replicating microorganisms.”
Life as we know it requires DNA. Dr. Mancinelli points out that nanobacteria-like particles obtained from human blood are able to withstand high doses of γ-irradiation up to 30 kGy. However, after performing broad-range polymerase chain reaction (PCR) amplifications to try to tease out a few strands of DNA, no bacterial DNA has been found. He goes on to suggest that CaCO3 (calcium carbonate) precipitates prepared in vitro are remarkably similar to purported nanobacteria “in terms of their uniformly sized, membrane-delineated vesicular shapes, with cellular division-like formations and aggregations in the form of colonies.” “Nanobacteria” in this context start to sound suspiciously like the colorful terraced rock formations found near Yellowstone’s Mammoth Hot Springs.
Where better to turn than SETI, the Search for Extraterrestrial Intelligence, to confirm the possible existence of organisms of extraterrestrial origin?
Unlike living organisms, these types of particles can be explained using simple inorganic chemistry. Dr. Mancinelli: “The gradual appearance of nanobacteria-like particles in incubated human serum as well as the changes seen with their size and shape can be influenced and explained by introducing varying levels of CO2 and NaHCO3 as well as other conditions known to influence the precipitation of CaCO3.”
Also, if nanobacteria are living disease vectors, then they should be attacked by monoclonal antibodies in the human immune system that target specific cells. “Western blotting [used to detect specific proteins in tissue] reveals that the monoclonal antibodies, claimed to be specific for nanobacteria, react in fact with serum albumin,” says Dr. Mancinelli. Serum albumin is the most abundant plasma protein in humans and other mammals. This evidence strongly suggests that nanobacteria are abiotic calcifying nanoparticles rather than living cells.
Nanoarchaea, however, are the real deal. Astrobiologist Karl Stetter discovered the nanoscale microbe, Nanoarchaeum equitans, off the coast of Iceland. This strange organism — known as a hyperthermophile — grows in temperatures that approach boiling and appears to be a symbiont of another microbe, Ignicoccus. N. equitans cannot synthesize most nucleotides, amino acids, lipids, and cofactors. It relies on its contact with its host organism to survive. Sequencing of the N. equitans genome reveals the smallest cellular genome (480 kb) presently known to man. “In contrast to typical genomes from parasitic/symbiotic microbes, that of N. equitans does not show any evidence of decaying genes and contains a full complement of tightly packed genes encoding informational proteins,” explains Mancinelli. “This suggests that the establishment of the dependence-relationship between N. equitans and Ignicoccus is probably very ancient.”
Dr. Mancinelli’s conclusions? While nanobacteria are abiotic with no evidence of DNA, ancient nanoarchaea have a full complement of genes. But neither, it turns out, are found in moon rocks or meteorites. “I know of no credible evidence that nanobacteria or nanoarchaea exist on meteorites,” says Mancinelli.
Nanobacteria, then, do not appear to rule the Earth and Mars at all. But thanks to SETI, the search for extraterrestrial life continues. Could our first encounter with life of non-Earth origin end up being with something as resilient as the hyperthermophile N. equitans?