Supposedly nanobacteria are cell-walled organisms much smaller than the generally accepted lower limits for cell size. The existence of nanobacteria has been a hot topic because of their putative roles in and heart disease and kidney stones.

There's even a company devoted to commercializing nanobacterial products: Nanobac. There's even a video of "nanobacteria" in action.

A new article in PLoS Pathogens says that's all balderdash. Here is the authors' summary:

"In the last decade, the exact nature of nanobacteria was one of the most controversial of scientific questions. An audacious theory proposed the existence of nanobacteria, initially discovered in Italian hot spring deposits, as a new life form responsible for a wide range of diseases in humans, thus qualifying them as new agents of emerging infectious diseases. The community of microbiologists remained therefore skeptical about the fact that such structures, 100 times smaller than bacteria and highly resistant to heat and other treatments that would normally kill the latter, could be living entities fully capable of self-replication. Other scientists wondered if they might be an unusual form of crystal rather than micro-organisms. The comprehensive characterization of nanobacteria was the focus of our study. Our results definitively ruled out the existence of nanobacteria as living entities and revealed that they correspond to self-propagating mineral-fetuin complexes that we called “nanons.”

If the authors are correct, the result is very interesting, despite putting a damper on hopes for a novel form of life. The authors suggest that the "nanobacteria" are in fact protein-mineral complexes, which no doubt precipitated confusion over their origins. The proteins in question, fetuins, are also known as binding proteins which mediate the transport and availability of a wide variety of substances in the blood stream. Usually they are known as potent inhibitors of sytemic calcification, so this new report is somewhat surprising.

The authors speculate:

"that the conformational change of the fetuin protein, equivalent to that observed in prions, can occur. This ... leads to a new 'pathogenic' fetuin isoform able to induce hydroxyapatite crystallization and to promote calcification."

If so, it would be highly novel and interesting. I don't believe, however, we have heard the last from the nanobacteria proponents, and this should be a controversial and interesting area of science for some time to come.

Photo: EM Analysis of Nanons Following Immunogold Staining (doi:10.1371/journal.ppat.0040041.g005)