MicroBiology-Draft/Sample

Class Alphaproteobacteria

Genus Microscopic

Morphology

Unique Characteristics

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 toCaulobacter

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

Table 4.2

1. What characteristic do all Alphaproteobacteria share?

Betaproteobacteria

Unlike Alphaproteobacteria, which survive on a minimal amount of nutrients, the classBetaproteobacteriaare
eutrophs (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 genusNeisseria, for example,
includes the bacteriaN. gonorrhoeae,the causative agent of the STI gonorrhea, andN. meningitides, the causative
agent of bacterial meningitis.

Chapter 4 | Prokaryotic Diversity 149