Nanobacterium is the unit or member name of a discredited former proposed class of living organisms, specifically cell-walled microorganisms, with a size much smaller than the generally accepted lower limit for life. Originally based on observed nano-scale structures in geological formations, some researchers suggested they were living organism capable of incorporating radiolabeled uridine, and others attributing to them a simpler, abiotic nature. One skeptic dubbed them "the cold fusion of microbiology", in reference to a notorious episode of supposed erroneous science. The term "calcifying nanoparticles" (CNPs) has also been used as a conservative name.