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Bacteria, Viruses, and Protists

Bacteria Basics

How many groups are identified in the domain Bacteria?

Biologists recognize at least a dozen different groups of bacteria. The following lists the major groups to date (for the explanation of a Gram reaction, see above):

Major Group

Gram Reaction

Characteristics

Examples

Actinomycetes

Positive

Produce spores and antibiotics; live in soil environment

Streptomyces

Chemoautotrophs

Negative

Live in soil environment; important in the nitrogen cycle

Nitrosomonas

Cyanobacteria

Negative

Contain chlorophyll and are capable of photosynthesis; live in aquatic environment

Anabaena

Enterobacteria

Negative

Live in intestinal and respiratory tracts; ability to decompose form spores; pathogenic

Escherichia, Salmonella, Vibrio

Gram-positive cocci

Positive

Live in soil environment; inhabit the skin and mucous membranes of animals; pathogenic to humans

Streptococcus, Staphylococcus

Gram-positive rods

Positive

Live in soil environment or animal intestinal tracts; anaerobic; disease-causing

Clostridia, Bacillus

Lactic acid bacteria

Positive

Important in food production, especially dairy products; pathogenic to animals

Lactobacillus, Listeria

Myxobacteria

Negative

Move by secreting slime and gliding; ability to decompose materials

Chondromyces

Pseudomonads

Negative

Aerobic rods and cocci; live in soil environment

Pseudomonas

Rickettsiae and Chlamydia

Negative

Very small, intracellular parasites; pathogenic to humans

Rickettsia, chlamydia

Spirochetes

Negative

Spiral-shaped, live in aquatic environment

Treponema, Borrelia



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