One of the two major classes of prokaryotic organism (the other being the Cyanobacteria). Bacteria are small (linear dimensions of around 1 m m), non-compartmentalised, with circular DNA, and ribosomes of 70S. Protein synthesis differs from that of eukaryotes, and many anti-bacterial antibiotics interfere with protein synthesis, but do not affect the infected host. Recently bacteria have been subdivided into Eubacteria and Archaebacteria, although some would consider the Archaebacteria to be a third kingdom, distinct from both Eubacteria and Eukaryotes. The Eubacteria can be further subdivided on the basis of their staining using Gram stain. Since the difference between Gram positive and Gram negative depends upon a fundamental difference in cell wall structure it is therefore more soundly based than classification on gross morphology alone (into cocci, bacilli, etc.).
Dictionary of molecular biology. 2004.