THE ânanobacteriaâ found in the Martian meteorite might be too small to be real bacteria â but that doesnât mean that extraterrestrial organisms arenât responsible for creating the diminutive fossils.
Jeff McLean at Pacific Northwest Labs in Richland, Washington, has found that iron-eating bacteria on Earth leave behind small sacs of enzymes when they detach themselves from a surface. These chemicals react with metals in rock, forming spherical mineral deposits around 100 nanometres across â 10 times smaller than normal bacteria. âTheir size, shape and arrangement are similar to the ânanobacteriaâ reported by McKay in the Martian meteorite,â says McLean.
The controversy has raged since Chris McKay made his claim in 1996. Most scientists believe the Martian âfossilsâ are far too small to be the remains of bacteria. âThe problem is they canât contain enough DNA to replicate themselves,â McLean says.
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When McLeanâs team grew metal-reducing bacteria on iron oxide particles, they found that sacs, or vesicles, budded off.
âThey hit a site and reduce all the iron that they can,â McLean says. âThen they want to find a new source of energy.â When they tear themselves away, they leave the vesicles behind. With a coating of minerals, they eventually form nanofossils, McLean says. âThere are reports of nanobacteria on Earth, too. These vesicles might explain some of them.â
âItâs a very interesting study,â says microbiologist Timothy Kral of the University of Arkansas in Fayetteville. But shape and size alone wonât prove the Martian fossils were formed by bacteria, he says.
