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Microbiology, 2021

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146 4 • Prokaryotic Diversity<br />

Table 4.4 summarizes the characteristics of important genera of Gammaproteobacteria.<br />

Class Gammaproteobacteria<br />

Example<br />

Genus<br />

Microscopic<br />

Morphology<br />

Unique Characteristics<br />

Beggiatoa<br />

Gram-negative<br />

bacteria; disc-shaped<br />

or cylindrical<br />

Aquatic, live in water with high content of hydrogen disulfide;<br />

can cause problems for sewage treatment<br />

Enterobacter<br />

Gram-negative<br />

bacillus<br />

Facultative anaerobe; cause urinary and respiratory tract<br />

infections in hospitalized patients; implicated in the<br />

pathogenesis of obesity<br />

Erwinia<br />

Gram-negative<br />

bacillus<br />

Plant pathogen causing leaf spots and discoloration; may digest<br />

cellulose; prefer relatively low temperatures (25–30 °C)<br />

Escherichia<br />

Gram-negative<br />

bacillus<br />

Facultative anaerobe; inhabit the gastrointestinal tract of warmblooded<br />

animals; some strains are mutualists, producing<br />

vitamin K; others, like serotype E. coli O157:H7, are pathogens;<br />

E. coli has been a model organism for many studies in genetics<br />

and molecular biology<br />

Hemophilus<br />

Gram-negative<br />

bacillus<br />

Pleomorphic, may appear as coccobacillus, aerobe, or facultative<br />

anaerobe; grow on blood agar; pathogenic species can cause<br />

respiratory infections, chancroid, and other diseases<br />

Klebsiella<br />

Gram-negative<br />

bacillus; appears<br />

rounder and thicker<br />

than other members<br />

of<br />

Enterobacteriaceae<br />

Facultative anaerobe, encapsulated, nonmotile; pathogenic<br />

species may cause pneumonia, especially in people with<br />

alcoholism<br />

Legionella<br />

Gram-negative<br />

bacillus<br />

Fastidious, grow on charcoal-buffered yeast extract; L.<br />

pneumophila causes Legionnaires disease<br />

Methylomonas<br />

Gram-negative<br />

bacillus<br />

Use methane as source of carbon and energy<br />

Proteus<br />

Gram-negative<br />

bacillus<br />

(pleomorphic)<br />

Common inhabitants of the human gastrointestinal tract; motile;<br />

produce urease; opportunistic pathogens; may cause urinary<br />

tract infections and sepsis<br />

Pseudomonas<br />

Gram-negative<br />

bacillus<br />

Aerobic; versatile; produce yellow and blue pigments, making<br />

them appear green in culture; opportunistic, antibiotic-resistant<br />

pathogens may cause wound infections, hospital-acquired<br />

infections, and secondary infections in patients with cystic<br />

fibrosis<br />

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