Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Gram-Negative Bacteria

  • Ricardo Amils
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_663-3


A Gram-negative bacterium is a prokaryotic cell with a cell wall containing small amounts of peptidoglycan and an outer membrane containing lipopolysaccharides, proteins, and other complex macromolecules. The distinction between Gram-positive and Gram-negative bacteriais based on a differential stain, the Gram stain, which depends on the structure of the cell wall (see cell wall). After Gram staining, Gram-positive bacteria appear purple and Gram-negative bacteria appear red. This difference in reaction to the Gram stain arises because of differences in the cell wall structure which promote the retention of the purple dye, crystal violet, in the Gram-positive bacteria after decoloring with ethanol, while in the Gram-negative bacteria, the stain is not retained. The Gram stain is one of the most useful staining procedures in microbiology. In addition to the peptidoglycan, Gram-negative bacteria contain an additional wall layer, the outer membrane. This layer is effectively...


Cell Wall Small Molecule Hydrolytic Enzyme Outer Membrane Bioorganic Chemistry 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Departamento de Biologia MolecularUniversidad Autónoma de MadridMadridSpain