Microbiology, 2021

142 4 • Prokaryotic Diversity
Betaproteobacteria
Betaproteobacteria are a diverse group of bacteria. The different bacterial species within this group utilize a
wide range of metabolic strategies and can survive in a range of environments. 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.
Neisseria are cocci that live on mucosal surfaces of the human body. They are fastidious, or difficult to culture,
and they require high levels of moisture, nutrient supplements, and carbon dioxide. Also, Neisseria are
microaerophilic, meaning that they require low levels of oxygen. For optimal growth and for the purposes of
identification, Neisseria spp. are grown on chocolate agar (i.e., agar supplemented by partially hemolyzed red
blood cells). Their characteristic pattern of growth in culture is diplococcal: pairs of cells resembling coffee
beans (Figure 4.5).
Figure 4.5
Neisseria meningitidis growing in colonies on a chocolate agar plate. (credit: Centers for Disease Control and Prevention)
The pathogen responsible for pertussis (whooping cough) is also a member of Betaproteobacteria. The
bacterium Bordetella pertussis, from the order Burkholderiales, produces several toxins that paralyze the
movement of cilia in the human respiratory tract and directly damage cells of the respiratory tract, causing a
severe cough.
Table 4.3 summarizes the characteristics of important genera of Betaproteobacteria.
Class Betaproteobacteria
Example
Genus
Microscopic
Morphology
Unique Characteristics
Bordetella
A small, gram-negative
coccobacillus
Aerobic, very fastidious; B. pertussis causes pertussis (whooping
cough)
Burkholderia
Gram-negative
bacillus
Aerobic, aquatic, cause diseases in horses and humans
(especially patients with cystic fibrosis); agents of nosocomial
infections
Leptothrix
Gram-negative,
sheathed, filamentous
bacillus
Aquatic; oxidize iron and manganese; can live in wastewater
treatment plants and clog pipes
Neisseria
Gram-negative, coffee
bean-shaped coccus
forming pairs
Require moisture and high concentration of carbon dioxide;
oxidase positive, grow on chocolate agar; pathogenic species
cause gonorrhea and meningitis
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