Nanobacteria

Nanobacteria is a term used to describe nanoscale particles claimed to be ultra-small bacteria-like organisms, typically reported in the tens to a couple hundred nanometers in diameter. The concept emerged in the late 1990s from the work of Kajander and colleagues, who reported finding such particles in human blood, urine, kidney stones, dental plaque, and other sources. They proposed that nanobacteria could replicate through a biomineralization process and speculated a role in calcific diseases such as kidney stones and vascular calcification.

Proponents attributed various biological-like properties to these particles, including self-replication and metabolism, and suggested links to pathological calcification in humans. They described isolation and growth under certain conditions and proposed that nanobacteria might contribute to diseases ranging from nephrolithiasis to atherosclerosis. The purported minuscule size and supposed ubiquity drew wide attention in both scientific and popular outlets.

The scientific response was highly controversial and largely critical. Independent researchers were unable to reproduce living cultures or obtain consistent evidence of cellular metabolism or genetic material. Critics argued that the observed particles were inorganic calcium phosphate–protein complexes formed abiotically, and that apparent growth could arise from crystallization or accretion rather than biological replication. Imaging artifacts and misinterpretations of mineral-protein aggregates were reported, leading many to reclassify nanobacteria as non-living mineral nanoparticles rather than true microbes.

Today the term nanobacteria is generally viewed with skepticism in mainstream microbiology, and it has largely fallen out of use. Research in related fields continues to explore biogenic mineralization and calcium phosphate nanoparticles, which can resemble cells but are not living organisms.