[Gr. archaios, ancient + bacteria]
A group of single-celled organisms, classified by some microbiologists as a type of bacteria and by others as a separate kingdom or domain of life. Unlike Eubacteria, they lack peptidoglycans in their cell walls. Their ribosomal RNA base sequences also differ from those found in Eubacteria. There are three divisions of archaebacteria: methanogens (organisms that produce methane), thermophiles (organisms that can live in extremely hot, acidic environments, e.g., sulfur springs), and halophiles (organisms that can live only in bodies of concentrated salt water, e.g., the Dead Sea).
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