An alternative interpretation of nanobacteria-induced biomineralization

The reported isolation of nanobacteria from human kidney stones raises the intriguing possibility that these microorganisms are etiological agents of pathological extraskeletal calcification [Kajander, E. O. & Ciftcioglu. N. (1998) Proc. Natl. Acad. Sci. USA 95, 8274-8279]. Nanobacteria were previou sly isolated from FBS after prolonged incubation in DMEM. These bacteria in itiated biomineralization of the culture medium and were identified in calc ified particles and biofilms by nucleic acid stains, 16S rDNA sequencing, e lectron microscopy. and the demonstration of a transferable biomineralizati on activity. We have now identified putative nanobacteria, not only from FB S, but also from human saliva and dental plaque after the incubation of 0.4 5-mu m membrane-filtered samples in DMEM. Although biomineralization in our "cultures" was transferable to fresh DMEM. molecular examination of decalc ified biofilms failed to detect nucleic acid or protein that would be expec ted from growth of a living entity. In addition, biomineralization was not inhibited by sodium azide. Furthermore, the 169 rDNA sequences previously a scribed to Nanobacterium sangoineum and Nanobacterium sp. were found to be indistinguishable from those of an environmental microorganism, Phyllobacte rium mysinacearum, that has been previously detected as a contaminant in PC R. Thus. these data do not provide plausible support for the existence of a previously undiscovered bacterial genus. Instead, we provide evidence that biomineralization previously attributed to nanobacteria may be initiated b y nonliving macromolecules and transferred on "subculture" by self-propagat ing microcrystalline apatite.