Life Cycle




EB - Elementary Bodies
RB - Reticulate Bodies

Fig 2. Multiple invasion of a laboratory-infected HeLa 229 cell. 
The matured infectious elementary body (i), 0.3 microns in size, 
has an electron dense "black" core of nucleic acid condensed 
onto chlamydial histone protein. By 3 hours after infection, 
some of the elementary bodies are already beginning to 
differentiate. Note at (ii) that the nucleic acid core is less marked; 
the spotty cytoplasm is due to the appearance of 
protein-synthesizing ribosomes. At (iii) the elementary body has 
enlarged further, the cytoplasm is less dense and the chlamydial 
DNA core even less prominent.



Fig 3. By 9 hours post infection, chlamydial endosomes containing
single, 1 micron,reticulate bodies (R) can be seen. These
originated from the differentiation of single elementary bodies.
Note that some of the chlamydiae have a division septum (ds)
and are already dividing by binary fission in typical bacterial manner.
Note also the  endosomal membrane (e) and the presence of many
vesicles of host cell membrane (m). At this stage the chlamydial
endosome enlarges by intercepting exocytic membrane traffic from
the Golgi apparatus.


Fig 4. A chlamydial inclusion 15 hours post infection containing 
many reticulate bodies (RB) of C. trachomatis LGV 404. Note the 
endosome membrane (em) and the blebs of membranous material
(mb) in the inclusion, probably derived from the reticulate body
outer envelope. Chlamydial lipopolysaccharide, exported from 
reticulate body inclusions, is the basis of some of the enzyme 
immunoassay tests for the diagnosis of chlamydial infection by the
detection of chlamydial antigen.


Fig 5. Thin section of part of the contents of a mature C. trachomatis
UW4  inclusion, 40 hours after infection of a HeLa 229 cell. The
picture shows the large, fragile, reticulate bodies (R), the smaller 
intermediate bodies (I) which develop from them with their 
characteristic condensed nucleoids of nucleic acid, and the 
slightly smaller elementary bodies (E) with their dense gene core.



Fig 6. Electron micrograph showing the connection of
three different reticulate bodies of C. psittaci Cal 10 
to the inclusion membrane. Tannic acid staining was
used to enhance the opacity of the projections which 
connect to, and penetrate, the inclusion membrane.



Fig 7. Carbon replica of a freeze-fractured face of a 
C. psittaci Cal 10 inclusion at 18 hours post infection. 
The arrows show the projections studding the inclusion 
membrane.



Fig 8. Some 18-22 hours post infection, reticulate 
bodies begin to differentiate again into elementary 
bodies (E), inside the chlamydial inclusion. The 
initial sign of this is the re-condensation of 
chlamydial nucleic acid on to histone protein. 
This stage is called the intermediate body, (I). 
Although it is usually thought that 1 reticulate 
body gives rise to 1 elementary body, often 
more than 1 elementary body may be formed 
as shown  in this photograph, where two 
intermediate bodies can be seen in the act 
of division. The intermediate bodies are 
approximately 0.5 microns in size. C.
trachomatis LGV 404.



Fig 9. Four mature elementary bodies surrounded by 
the envelope of the reticulate body that produced them.



Fig 10. Mature inclusion of C. trachomatis LGV 404 in a 
BGMK cell, 48 hrs after infection. The cell cytoplasm is
packed with small, dark-staining, chlamydial elementary 
bodies and the larger, grey, decaying remains of the 
chlamydial reticulate bodies that produced them. The 
host cell nucleus has been pushed into the left-hand 
corner of the cell.



Fig 11. Beautiful "comets" of 48 hr mature inclusions of C. trachomatis 
LGV 404 in HeLa 229 cells. The preparation has been stained with Hoechst 
33258, which forms a fluorescent complex in DNA. Round or kidney 
bean-shaped host cell nuclei can be seen together with tiny dots of 
fluorescing chlamydial elementary bodies. The comet "body" is made 
of DNA-containing, fluorescent chlamydial particles packed into mature 
cytoplasmic inclusions.


Fig 12.  A HeLa 229 cell infected for 40 hrs with C. 
trachomatis LGV 404, critical point dried, then 
freeze-fractured open. Ice has removed most of 
the chlamydial particles, revealing the inclusion 
membrane. Chlamydiae extensively modify this 
membrane with Inc and other proteins. The 
inclusion membrane enlarges by intercepting 
exocytic membrane vesicles from the host cell's 
Golgi apparatus.



Fig 13. Specimen and preparation as for Fig 10. Detail 
of the freeze-fractured interior of a mature chlamydial 
inclusion showing, slightly left of centre, the decaying 
remains of a reticulate body surrounded by membrane 
blebs of chlamydial antigen similar to those in Fig 4. 
The small round structures are chlamydial elementary 
bodies and the fine granular matrix is due to the 
glycogen-like reserve carbohydrate that C. trachomatis 
deposits in inclusions.


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