One of the three major domains of living organisms, comprising aerobic and anaerobic bacteria occurring in virtually all habitats. Some live in or on the bodies of other organisms, and may cause disease. Eubacteria are now regarded as being quite distinct, in evolutionary terms, from the other group of prokaryotes, the archaebacteria (see Archaea). This is based mainly on comparisons of the nucleotide sequences of ribosomal RNA (see molecular systematics). However, eubacteria have other defining characteristics. For example, virtually all have cell walls containing peptidoglycan, and their membrane lipids contain fatty acids in ester linkage to glycerol, whereas archaebacteria lack peptidoglycan and have ether-linked lipids.