MicroBiology-Draft/Sample

Chlamydiais another taxon of the Alphaproteobacteria. Members of this genus are extremely resistant to the cellular
defenses, giving them the ability to spread from host to host rapidly via elementary bodies. The metabolically and
reproductively inactiveelementarybodiesaretheendospore-like formofintracellular bacteria thatenteranepithelial
cell, where they become active.Figure 4.5illustrates the life cycle ofChlamydia.

C. trachomatisis a human pathogen that causes trachoma, a disease of the eyes, often leading to blindness.C.
trachomatisalso causes the sexually transmitted disease lymphogranuloma venereum (LGV). This disease is often
mildly symptomatic, manifesting as regional lymph node swelling, or it may be asymptomatic, but it is extremely
contagious and is common on college campuses.

Table 4.2summarizes the characteristics of important genera of Alphaproteobacteria.

Figure 4.5 Chlamydiabegins infection of a host when the metabolically inactive elementary bodies enter an
epithelial cell. Once inside the host cell, the elementary bodies turn into active reticulate bodies. The reticulate bodies
multiply and release more elementary bodies when the cell dies after theChlamydiauses all of the host cell’s ATP.

Class Alphaproteobacteria

Genus Microscopic

Morphology

Unique Characteristics

Agrobacterium Gram-negative bacillus Plant pathogen; one species,A. tumefaciens, causes tumors in

plants

Table 4.2

148 Chapter 4 | Prokaryotic Diversity

This OpenStax book is available for free at http://cnx.org/content/col12063/1.2