Researchers fail to find signs of life in 'living' particles

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Despite their tiny size, the purported pathogenic microorganisms dubbed 'nanobacteria' are still stirring big controversy in microbiological circles.

A report published in Proceedings of the National Academy of Sciences last month (97, 11511–11515; 2000) has failed to confirm biochemical signs of life in the apparently self-replicating particles.

Finnish biochemist Olavi Kajander of the University of Kuopio believes the particles, which are 50–500 nanometres in diameter, are a new type of microorganism. He says that they could be involved in kidney disease. (Nature 401, 105; 1999).

The particles all have coats of heavy hydroxyapatite, the mineral that forms teeth and kidney stones. According to Kajander, this coat makes them resistant to attack from environmental assaults — and also to standard microbial and biochemical analysis. But he says the particles appear to be living because microscope analysis reveals broad similarity to bacteria. He also says that they stain for DNA, using a modification of a standard method.

Now some of his experiments have been repeated independently. John Cisar of the US National Institutes of Health in Bethesda, and colleagues from the Food and Drug Administration, have created the particles and reproduced their self-propagating properties.

But the researchers say that the particles' self-propagation and morphology can be explained in terms of microcrystallization, independent of any 'living' mechanism. They could not detect any nucleic acids or proteins in the particles. Moreover, the self-propagation was unaffected by sodium azide, which inhibits respiration. Cisar says that “there is a need for hard molecular evidence” to support a claim for a biological base.

Kajander and his colleagues, including some clinical researchers, counter that the special properties of nanobacteria mean that standard biochemical analyses are not necessarily applicable. “We have evidence that the particles are living,” insists Neva Çiftçioglu, also at Kuopio. “We are not fanatics, we are scientists.”

And Franklin Cockerill, chair of microbiology at the Mayo Clinic, Rochester, says he will continue trying to extract DNA from the nanobacteria. He hopes to sequence the genome for the particles, which, he suggests, could indicate the smallest number of genes required for life.

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