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C. trachomatis is a human pathogen that causes trachoma , a disease of the eyes, often leading to blindness. C. trachomatis also 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.

[link] summarizes the characteristics of important genera of Alphaproteobacteria.

A diagram showing the life cycle of Chlamydia. An epithelial cell is infected by small spheres labeldd elementary bodies. Within 12 hours, these form into reticulate bodies which divide  to form inclusions within 24 hours. Within the inclusions more elementary bodies are formed and within 72 hours these are released when the cell ruptures.
Chlamydia begins 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 the Chlamydia uses all of the host cell’s ATP. (credit: modification of work by Centers for Disease Control and Prevention)
Class Alphaproteobacteria
Genus Microscopic Morphology Unique Characteristics
Agrobacterium Gram-negative bacillus Plant pathogen; one species, A. tumefaciens , causes tumors in plants
Bartonella Gram-negative, pleomorphic, flagellated coccobacillus Facultative intracellular bacteria, transmitted by lice and fleas, cause trench fever and cat scratch disease in humans
Brucella Gram-negative, small, flagellated coccobacillus Facultative intracellular bacteria, transmitted by contaminated milk from infected cows, cause brucellosis in cattle and humans
Caulobacter Gram-negative bacillus Used in studies on cellular adaptation and differentiation because of its peculiar life cycle (during cell division, forms “swarm” cells and “stalked” cells)
Chlamydia Gram-negative, coccoid or ovoid bacterium Obligatory intracellular bacteria; some cause chlamydia, trachoma, and pneumonia
Coxiella Small, gram-negative bacillus Obligatory intracellular bacteria; cause Q fever; potential for use as biological weapon
Ehrlichia Very small, gram-negative, coccoid or ovoid bacteria Obligatory intracellular bacteria; can be transported from cell to cell; transmitted by ticks; cause ehrlichiosis (destruction of white blood cells and inflammation) in humans and dogs
Hyphomicrobium Gram-negative bacilli; grows from a stalk Similar to Caulobacter
Methylocystis Gram-negative, coccoid or short bacilli Nitrogen-fixing aerobic bacteria
Rhizobium Gram-negative, rectangular bacilli with rounded ends forming clusters Nitrogen-fixing bacteria that live in soil and form symbiotic relationship with roots of legumes (e.g., clover, alfalfa, and beans)
Rickettsia Gram-negative, highly pleomorphic bacteria (may be cocci, rods, or threads) Obligate intracellular bacteria; transmitted by ticks; may cause Rocky Mountain spotted fever and typhus
  • What characteristic do all Alphaproteobacteria share?


Unlike Alphaproteobacteria, which survive on a minimal amount of nutrients, the class Betaproteobacteria are eutroph s (or copiotrophs), meaning that they require a copious amount of organic nutrients. Betaproteobacteria often grow between aerobic and anaerobic areas (e.g., in mammalian intestines). Some genera include species that are human pathogens, able to cause severe, sometimes life-threatening disease. The genus Neisseria , for example, includes the bacteria N. gonorrhoeae, the causative agent of the STI gonorrhea , and N. meningitides , the causative agent of bacterial meningitis .

Questions & Answers

reactions if viruses to physical and chemical agents?
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
not 'things'...'organisms' like bacterias, viruses and fungi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
bacterium is obvio in a singular form but plural of bacterium is bacterias
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
what is microbiology?
Sandeep Reply
what is microbiology
is the study of small microorganisms that can't be viewed by our naked eyes under a microscope
it's the study of microbes their classification, diversity, their cellular structure and processes, their applications and interaction with other organisms.
what is EMP pathway
which organism is implicated in meningoencephalitis
Peter Reply
Herpes virus
which mold is called dairy mold?
Geotrichum candidum
which infectious agent is the smallest
spore or virus
prion ....it is a single protein in a misfolded form..there is also a theory based on it
yup...m sry
yes it can be turned as a virus
which gram positive bacteria is responsible for food poisoning?
prion is not a living organism yet it is infectoois why
prions are virus like organism. and it is a misfolded protein that may cause disease to us.
Clostridium perfringens, B.cereus
Who is the father of the biology
I have one more question. . that who is the father of botany and medicine? ? can any one tell
define polar bond in simple way
Rashmi Reply
when there is formation of positive and negative poles i.e. one atom is +ve and other is -ve which further results in the dipole moment. Such bond is know as polar bond. It is a convalent bond only.
Hi everyone, is these site only about microbiology? I want a site which I can download articles on hematological and biochemical profile
Peter Reply
I think it is only about micro biology.
so whats happening
I am about to enter school and am going for MCB
Olugbenga Reply
What is DNA damage and repair
Sree Reply
removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
replication is a term related to generation of new DNA from a parental DNA.
role of microorganism as pathogens
Parteek Reply
to live inside the host body, reproduction n destroy the immune system of host body.
what is replication
please give me ans
replication is a term related to generation of new DNA from parental DNA.
difference between endotoxin and exotoxin
Binkheir Reply
toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
Generally, exotoxins are produced by gram positive bacteria and endotoxins are the integral part of the cell wall of gram negative bacteria. But some gram negative bacteria can also produced exotoxins such as E.coli.
Yeah u r ryt aakarti exotoxins screted by gram postive bacteria nd secreted by cell surface and they are secondary metabolites ....On the other hand endotoxin released by gram negtive bacteria nd released inside the cell (lipopolysaccharide) ..
Heat stable lipopolysaccharides to be exact.
please I want the names of bacteria and the diseases they cause.
Ibrahim Reply
there are many we classify it according to their shapes gram negative or gram positive
so u may refer the book u guess or by when u want I can do a list for you and send u here
please do a list for me
I have the lost but it's too much to type ..
MSc entrance prepare books and questions LA etha base pani irukum..
Guhan Reply
kushal always prescott is the imp book to follow.search some objective mcqs books based on your syllabus
deepthi Reply
I want to clear entrance of ms university so I have no more idea so my preparation is based on my bachlor studies.
what are the opportunistic infection in aids stage
certain cancer or pneumonia 🤔
penicillium crysogenum
Kushal Reply

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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