[[Ficheiro:Gram negative cell wall.svg|miniatura|dereita|250px|[[Parede celular]] dunha bacteria [[Gram negativa]].]]
O '''espazo periplásmico''' ou '''periplasma''' é o espazo que rodea a dúas barreiras de permeabilidade selectiva na cuberta das bacterias, como son a [[membrana plasmática]] ou membrana interna e a membrana externa das paredes das bacterias [[Gram negativa]]s. StrictlyFalando speakingestritamente, thereas is no '''periplasmic space''' inbacterias [[Gram-positive positiva]]s [[bacterium|bacteria]]non becauseteñen thereun isverdadeiro onlyespazo oneperiplásmico biologicalporque membraneteñen só unha membrana biolóxica lipoproteica, thea [[cytoplasmicmembrana membraneplasmática]], butpero apoden ter unha rexión regiondenominada termed"zona da parede interna" (IWZ, '''inner wall zone (IWZ)''') hassituada beenentre observeda betweenmembrana theplasmática [[cytoplasmice membrane]] and the maturea [[cellparede wall]celuklar5]+ madura. <ref name="Matias & Beveridge, 2005">, Matias, V. R., and T. J. Beveridge. 2005. Cryo-electron microscopy reveals native polymeric cell wall structure in Bacillus subtilis 168 and the existence of a periplasmic space. Mol. Microbiol. 56:240-251. {{doi|10.1111/j.1365-2958.2005.04535.x}}.</ref><ref name="Zuber et al, 2006">, Zuber B, Haenni M, Ribeiro T, Minnig K, Lopes F, Moreillon P, Dubochet J. 2006. Granular layer in the periplasmic space of Gram-positive bacteria and fine structures of Enterococcus gallinarum and [[Streptococcus gordonii]] septa revealed by cryo-electron microscopy of vitreous sections. J Bacteriol. 188:6652-6660. {{doi|10.1128/JB.00391-06}}</ref>
The '''periplasm''' may constitute up to 40% of the total cell volume in [[Gram-negative]] species, whereas the '''IWZ''' is drastically smaller in [[Gram-positive]] species.<ref name="isbn3-540-42608-6">{{cite book |author=Otto Holst; Guntram Seltmann |title=The Bacterial Cell Wall |publisher=Springer |location=Berlin |year= |pages= |isbn=3-540-42608-6 |oclc= |doi=}}</ref> Composition of the '''IWZ''' has not been as yet clearly determined.
