Farooq A ShiekhAix-Marseille Université, URMITE, UMR, CNRS 7278, IRD 198, Marseille, FranceWith great interest, I read a recent article published in the International Journal of Nanomedicine by Guo et al.1 This study involved an analysis of calcifying nanoparticles to determine the presence of unique 16S rDNA. Nanoparticles that have since been isolated from biological samples have properties that appear to be consistent with a novel life form, including "self-replication". However, despite a large body of intriguing and suggestive evidence, the true biological nature of nanoparticles has been elusive, and in the past decade this subject has spurred one of the biggest controversies in modern microbiology.2 First, the results published in the Proceedings of the National Academy of Sciences by Cisar et al reached a completely opposite conclusion to the original assertion by Kajander and Ciftçioglu, which identified nanobacteria as living organisms.3,4 In addition, a closer look at the 16S rDNA sequences previously ascribed to so-called nanobacterial species showed that they are virtually identical to those of a notorious contaminating microorganism, Phyllobacterium mysinacearum. Second, after this report, multiple evidence-based studies were conducted in order to better understand the actual biological composition and self-propagation of nanobacteria.5–7 None of these findings are conclusive; however, biological insights of this mystery are now emerging.View original paper by Guo and colleagues.