The BBC has an interesting article on nanobacteria. Or possible nanobacteria. They're smaller than the minimum size something can be, and have DNA in it (we think). They appear to replicate in a culture, yet tests for the presence of Nucleic Acids have been inconclusive or negative.
"I don't see any convincing evidence for nannobacteria or DNA [in this study]," Dr John Cisar, of the National Institutes of Health in Bethesda, US, told BBC News Online.
"If you know you're dealing with a life form, you can use the staining techniques [they used]. But there are false positives in these types of techniques."
Dr Cisar said in research he had conducted, nanoparticles had tested positive with a stain for nucleic acids. But when he and his team tried to extract these nucleic acids, none had been found.
Previous research carried out by Jack Maniloff of the University of Rochester in New York has shown that to contain the DNA and proteins it needs to function, a cell must be a minimum of 140nm across.
"One of the questions we always get back is: 'well, how do you know it's alive if it doesn't have a unique DNA sequence?' This is true," Dr Miller explained.
"But if you go back to how we defined life prior to our knowing about DNA, our criteria was that things multiplied in culture. This is what we have."
In 1996, nannobacteria came to the attention of the world's media when scientists announced they had found fossils in a Martian meteorite of what appeared to be nano-sized bacteria.
Scientists are now involved in efforts to isolate DNA from the nanoparticles.