Chlamydiia Horn 2016
General information
Description and emendation
Members of the class Chlamydiia have the following common features: an obligate intracellular life style, the absence of flagella and peptidoglycan, and a proteinaceous cell wall. The class Chlamydiia contains but a single order, the Chlamydiales.
1: The class Chlamydiia contains the orders Chlamydiales and Parachlamydiales. Organisms within the class Chlamydiia are Gram-negative, aflagellar, obligate intracellular bacterial parasites of eukaryotic hosts. Chlamydiia have distinctive cell envelope structures in which peptidoglycan may be found and proteinaceous components are significant. Chlamydiia possess a unique biphasic development cycle. Multiplication within the eukaryotic host cell is characterized by reorganization of a small, rigid walled, metabolically inactive, infectious form (elementary body) into a large flexible walled, metabolically active, generally non-infectious form (reticulate body) that is capable of binary fission. Reticulate bodies reorganize into elementary bodies that survive extracellularly to infect new host cells upon their release from the host cell. Members of this class typically show >80% 16S rRNA gene sequence identity with each other. The members of the class Chlamydiia form a cluster in phylogenetic trees that is clearly separated from all other bacterial organisms and are also distinguished from all other bacteria by the CSIs.