Anton G Kutikhin, Elena B Brusina, Arseniy E Yuzhalin

Calcifying nanoparticles (CNPs) (nanobacteria, nanobacteria-like particles, nanobes) were discovered over 25 years ago; nevertheless, their nature is still obscure. To date, nobody has been successful in credibly determining whether they are the smallest self-replicating life form on Earth, or whether they represent mineralo-protein complexes without any relation to living organisms. Proponents of both theories have a number of arguments in favor of the validity of their hypotheses. However, after epistemological analysis carried out in this review, all arguments used by proponents of the theory about the physicochemical model of CNP formation may be refuted on the basis of the performed investigations, and therefore published data suggest a biological nature of CNPs. The only obstacle to establish CNPs as living organisms is the absence of a fairly accurately sequenced genome at the present time. Moreover, it is clear that CNPs play an important role in etiopathogenesis of many diseases, and this association is independent from their nature. Consequently, emergence of CNPs in an organism is a pathological, not a physiological, process. The classification and new directions of further investigations devoted to the role of CNPs in biology and medicine are proposed.