THE 鈥渘anobacteria鈥� found in the Martian meteorite might be too small to be real bacteria 鈥� but that doesn鈥檛 mean that extraterrestrial organisms aren鈥檛 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 鈥� 10 times smaller than normal bacteria. 鈥淭heir size, shape and arrangement are similar to the 鈥榥anobacteria鈥� reported by McKay in the Martian meteorite,鈥� says McLean.
The controversy has raged since Chris McKay made his claim in 1996. Most scientists believe the Martian 鈥渇ossils鈥� are far too small to be the remains of bacteria. 鈥淭he problem is they can鈥檛 contain enough DNA to replicate themselves,鈥� McLean says.
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When McLean鈥檚 team grew metal-reducing bacteria on iron oxide particles, they found that sacs, or vesicles, budded off.
鈥淭hey hit a site and reduce all the iron that they can,鈥� McLean says. 鈥淭hen they want to find a new source of energy.鈥� When they tear themselves away, they leave the vesicles behind. With a coating of minerals, they eventually form nanofossils, McLean says. 鈥淭here are reports of nanobacteria on Earth, too. These vesicles might explain some of them.鈥�
鈥淚t鈥檚 a very interesting study,鈥� says microbiologist Timothy Kral of the University of Arkansas in Fayetteville. But shape and size alone won鈥檛 prove the Martian fossils were formed by bacteria, he says.
