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Chapter 19
Bacteria & Viruses
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19–1 Bacteria
• Prokaryote = single-celled organism lacking
a nucleus
• 1 to 5 micrometers
• Epulopiscium fishelsoni
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Classifying Prokaryotes
• Monera  eubacteria and archaebacteria
• Eubacteria: - Larger kingdom, live almost
everywhere
E. Coli
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Archaebacteria
• lack peptidoglycan
• different membrane lipids
• the DNA sequences of key archaebacterial
genes are more like those of eukaryotes
than those of eubacteria
• Live in extreme environments
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Identifying Prokaryotes
• Identified by:
– shape
– the chemical nature of their cell walls
– the way they move
– the way they obtain energy
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Shapes
• Rod-shaped prokaryotes are called bacilli
(singular:bacillus).
• Spherical prokaryotes are called cocci
(singular: coccus).
• Spiral and corkscrew-shaped prokaryotes
are called spirilla (singular: spirillum).
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Cell Walls & Movement
• Cell Walls:
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with or without peptidoglycan
Use violet and red stains to detect
Gram + (violet) = with
Gram – (red) = without
• Movement:
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No movement
Flagella = whip like
lash, snake, or spiral forward
glide slowly along a layer of slimelike material they
secrete
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Metabolic Diversity
• Most heterotrophs, some autotrophs
• Heterotrophs:
– Chemoheterotroph - Most heterotrophic
prokaryotes must take in organic molecules for
both energy and a supply of carbon.
– Photoheterotroph = organism that is
photosynthetic but needs organic compounds
as a carbon source
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• Autotrophs:
– Photoautotroph =
organism that uses
energy from sunlight to
convert carbon dioxide
and water to carbon
compounds
• Ex: Cyanobacteria
– Chemoautotroph =
organism that makes
organic carbon
molecules from carbon
dioxide using energy
from chemical reactions
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Releasing Energy
• Obligate aerobe = organism that requires a
constant supply of oxygen in order to live
• “Obligated” means they are required to have
or do something
– Ex: Mycobacterium tuberculosis
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• Obligate anaerobe = organism that cannot
live in the presence of oxygen.
– ex: Clostridium botulinum
• grow in canned food that has not been properly
sterilized
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• Facultative anaerobe = organism that can
survive with or without oxygen
• “Facultative” means able to function in
different ways depending on the
environment
– Ex: E. coli
• lives anaerobically in the large intestine and
aerobically in sewage or contaminated water
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Growth and Reproduction
• Binary Fission = type of asexual reproduction
in which an organism replicates its DNA and
divides in half, producing two identical
daughter cells
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• Conjugation = form of sexual reproduction
in which paramecia and some prokaryotes
exchange genetic information
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• Spore Formation = When growth
conditions become unfavorable, many
bacteria form structures called spores
– endospore = type of spore formed when a
bacterium produces a thick internal wall that
encloses its DNA and a portion of its cytoplasm
• remain dormant for months or even
years
• conditions improve, the endospore
will germinate
• survive harsh conditions
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Endospores
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• Nitrogen Fixers = bacteria
• nitrogen fixation = process of converting
nitrogen gas into ammonia
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The Role of
Microorganisms in
Maintaining Equilibrium in
the Environment
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Importance of bacteria
Bacteria are vital to maintaining the
living world.
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Helpful Bacteria
• Decomposers break down dead organic
material
• Biotechnology - inserting helpful genes into
a plasmid
• Bioremediation - bacteria eat up oil spills
• Food production
• Put nitrogen back into the soil
• Aid in digestion
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Importance of Bacteria
• MANY uses!!
• Decomposers - bacteria help the ecosystem
recycle nutrients; sewage treatment
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Importance of bacteria
Some are producers that capture
energy by photosynthesis.
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Importance of bacteria
Others are decomposers breaking down
nutrients in dead matter.
Bacteria breakdown dead and decaying
organisms.
Help to recycle nutrients – which helps to
maintain equilibrium in the environment.
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Importance of bacteria
Bacteria are also used to make some foods such as: pickles, ice cream,
yogurt, and other things.
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Cheese: Bacteria produce lactic acid, which initially thickens the milk;
bacteria also determine the flavor of the cheese later in the ripening
process.
Bread (leavened): Made using yeast, although the byproducts of the
yeast’s fermentation of the dough are water and carbon dioxide (not
alcohol), which fills the dough with air bubbles that make it rise
Pickles: Cucumbers are fermented using lactic acid producing bacteria,
giving pickles their sour taste and also preventing harmful strains of
bacteria from taking hold. Microbes used: Enterobacter aerogenes,
Lactobacillus brevis and L. plantarum, Leuconostoc mesenteroides,
Pediococcus cerevisiae, Enterococcus faecalis
Olives: Basically inedible until they are fermented, olives are also
fermented using lactic acid producing bacteria, including Lactobacillus
brevis, Lactobacillus plantarum. and Leuconostoc
Yogurt: Bacteria added to milk produce lactic acid that makes the yogurt
sour and partially breaks down the lactose in the milk. Microbes used:
Lactobacillus bulgaricus and/or acidophilus & Streptococcus thermophilus
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