- Clostridiaspp. are low G+C gram-positive bacteria that are generally obligate anaerobes and can form
endospores. Pathogens in this genus includeC. perfringens(gas gangrene),C. tetani(tetanus), andC.
botulinum(botulism). - Lactobacillales include the genera Enterococcus, Lactobacillus, Leuconostoc, and Streptococcus.
Streptococcusis responsible for many human diseases, including pharyngitis (strep throat), scarlet fever,
rheumatic fever, glomerulonephritis, pneumonia, and other respiratory infections. - Bacilli is a taxonomic class of low G+C gram-positive bacteria that include rod-shaped and coccus-shaped
species, including the generaBacillusandStaphylococcus.B. anthraciscauses anthrax,B. cereusmay cause
opportunistic infections of the gastrointestinal tract, andS. aureusstrains can cause a wide range of infections
and diseases, many of which are highly resistant to antibiotics. - Mycoplasmaspp. are very small,pleomorphiclow G+C gram-positive bacteria that lack cell walls.M.
pneumoniaecauses atypical pneumonia.
4.5 Deeply Branching Bacteria
- Deeply branching bacteriaare phylogenetically the most ancient forms of life, being the closest to the last
universal common ancestor. - Deeply branching bacteria include many species that thrive in extreme environments that are thought to
resemble conditions on earth billions of years ago - Deeply branching bacteria are important for our understanding of evolution; some of them are used in industry
4.6 Archaea
- Archaeaare unicellular, prokaryotic microorganisms that differ from bacteria in their genetics, biochemistry,
and ecology. - Some archaea are extremophiles, living in environments with extremely high or low temperatures, or extreme
salinity. - Only archaea are known to produce methane. Methane-producing archaea are calledmethanogens.
- Halophilic archaea prefer a concentration of salt close to saturation and perform photosynthesis using
bacteriorhodopsin. - Some archaea, based on fossil evidence, are among the oldest organisms on earth.
- Archaea do not live in great numbers in human microbiomes and are not known to cause disease.
Review Questions
Multiple Choice
- The term prokaryotes refers to which of the
following?
a. very small organisms
b. unicellular organisms that have no nucleus
c. multicellular organisms
d. cells that resemble animal cells more than plant
cells - The term microbiota refers to which of the
following?
a. all microorganisms of the same species
b. all of the microorganisms involved in a
symbiotic relationship
c. all microorganisms in a certain region of the
human body
d. all microorganisms in a certain geographic
region
3. Which of the following refers to the type of
interaction between two prokaryotic populations in
which one population benefits and the other is not
affected?
a. mutualism
b. commensalism
c. parasitism
d. neutralism
4. Which of the following describes Proteobacteria in
domain Bacteria?
a. phylum
b. class
c. species
d. genus
Chapter 4 | Prokaryotic Diversity 179