Nanobacterium (/ˌnænoʊbækˈtɪəriəm/ NAN-oh-bak-TEER-ee-əm, pl. nanobacteria /ˌnænoʊbækˈtɪəriə/ NAN-oh-bak-TEER-ee-ə) is the unit or member name of a former proposed class of living organisms, specifically cell-walled microorganisms, now discredited, with a size much smaller than the generally accepted lower limit for life (about 200 nm for bacteria, like mycoplasma). Originally based on observed nano-scale structures in geological formations (including one meteorite), the status of nanobacteria was controversial, with some researchers suggesting they are a new class of 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 suppos