Microbiology

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Chapter 11

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General Characteristics of Prokaryotic
Organisms
• Prokaryotes
• Most numerous and diverse group of cellular microbes
• Thrive in various habitats
• Only a few are capable of colonizing humans and
causing disease

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Figure 11.1 Typical prokaryotic morphologies.

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General Characteristics of Prokaryotic
Organisms
• Endospores
• Produced by Gram-positive bacteria Bacillus and
Clostridium
• Each vegetative cell transforms into one endospore
• Each endospore germinates to form one vegetative cell
• Defensive strategy against unfavorable conditions
• Endospores are often difficult to kill
• Concern to food processors, health care professionals,
and governments

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Endospore
Vegetative
cell
Endospore
Figure 11.2 Locations of endospores.

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General Characteristics of Prokaryotic
Organisms
• Reproduction of Prokaryotic Cells
• All reproduce asexually
• Several different methods
• Binary fission (most common)
• Snapping division
• Reproductive spores
• Budding
• Viviparity

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Bacterial Growth: Overview

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Cell replicates its DNA.
Nucleoid
1
The cytoplasmic
membrane elongates,
separating DNA
molecules.
Cross wall forms;
membrane
invaginates.
Cross wall forms
completely.
Daughter cells
may separate.
2
3
4
5
Cell wall
Cytoplasmic
membrane
Replicated
DNA
Figure 11.3 Binary fission.

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Older, outer portion
of cell wall
Newer, inner portion
of cell wall
Ruptured
remains
of old cell
wall
Hinge
Figure 11.4 Snapping division, a variation of binary fission.

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Figure 11.5 Spores of actinomycetes.
Spores
Filamentous
vegetative cells

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Figure 11.6 Budding.

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General Characteristics of Prokaryotic
Organisms
• Reproduction of Prokaryotic Cells
• Epulopiscium and its relatives have unique method of
reproduction
• Live offspring emerge from the body of the dead mother
cell (viviparity)
• First noted case of viviparous behavior in prokaryotic world

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Figure 11.7 Viviparity in Epulopiscium.

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General Characteristics of Prokaryotic
Organisms
• Arrangements of Prokaryotic Cells
• Result from two aspects of division during binary fission
• Planes in which cells divide
• Separation of daughter cells

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Plane of division
Diplococci
Streptococci
Tetrads
Sarcinae
Staphylococci
Figure 11.8 Arrangements of cocci.

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Single bacillus
Diplobacilli
Streptobacilli
Palisade
V-shape
Figure 11.9 Arrangements of bacilli.

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General Characteristics of Prokaryotic
Organisms
• Tell Me Why
• Why does binary fission produce chains of cocci in
some species but clusters of cocci in other species?

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Modern Prokaryotic Classification
• Currently based on genetic relatedness of rRNA
sequences
• Three domains
• Archaea
• Bacteria
• Eukarya
• Bergey's Manual of Systematic Bacteriology
provides prokaryotic classification scheme

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Figure 11.10 Prokaryotic taxonomy.
Thermophilic
bacteria
PHYLUM CHLOROFLEXI
(green nonsulfur)
BACTERIA
GRAM-NEGATIVE BACTERIA
PHYLUM PROTEOBACTERIA
Nitrogen fixing (α)
Rickettsias (α)
PHYLUM
CHLOROBI
(green
sulfur)
PHYLUM
BACTEROIDETES
PHYLUM
PLANCTOMYCETES
Low G+C Gram-positive
PHYLUM FIRMICUTES
PHYLUM
CHLAMYDIAE
PHYLUM
SPIROCHAETES
Neisserias (β)
PHYLUM
FIBROBACTERES
Mycoplasmas Bacilli, lactobacili, cocci
Clostridia
Arthrobacter
Corynebacterium
Mycobacterium
Nocardia
Thermophilic
archaea
TIME
Halophiles
Methanogens
PHYLUM EURYARCHAEOTA
ARCHAEA
Atopobium
Streptomyces
Selenomonas
PHYLUM FUSOBACTERIA
Gammaproteobacteria (γ)
Campylobacteria (ε)
Myxobacteria (δ)
Nitrifying (β)
Purple nonsulfur (α)
PHYLUM DEINOCOCCUS-THERMUS
Deeply branching bacteria
PHYLUM AQUIFICAE
PHYLUM CYANOBACTERIA
PHYLUM
CRENARCHAEOTA
GRAM-POSITIVE BACTERIA
PHYLUM ACTINOBACTERIA
High G+C Gram-positive

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Modern Prokaryotic Classification
• Tell Me Why
• Why are taxonomic names and categories in our current
taxonomic scheme different from those in 1990?

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Survey of Archaea
• Common features
• Lack true peptidoglycan
• Cell membrane lipids have branched hydrocarbon chains
• AUG codon codes for methionine
• Two phyla: Crenarchaeota, Euryarchaeota
• Reproduce by binary fission, budding, or fragmentation
• Are cocci, bacilli, spirals, or pleomorphic
• Not known to cause disease

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Figure 11.11 Archaea.

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Survey of Archaea
• Extremophiles
• Require extreme conditions to survive
• Temperature, pH, and/or salinity
• Prominent members are thermophiles and halophiles

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Survey of Archaea
• Extremophiles
• Thermophiles
• DNA, RNA, cytoplasmic membranes, and proteins do not
function properly below 45ºC
• Hyperthermophiles – require temperatures over 80ºC
• Two representative genera
• Geogemma
• Pyrodictium

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Figure 11.12 Some hyperthermophilic archaea live in hot springs.

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Survey of Archaea
• Extremophiles
• Thermophiles
• Thermophilic enzymes are used for research and
industrial applications
• Recombinant DNA technologies
• Additives in laundry detergents

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Survey of Archaea
• Extremophiles
• Halophiles
• Inhabit extremely saline habitats
• Depend on greater than 9% NaCl to maintain integrity of
cell walls
• Many contain red or orange pigments
• May protect from sunlight
• Most studied – Halobacterium salinarium

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Figure 11.13 The habitat of halophiles: highly saline water.

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Survey of Archaea
• Extremophiles
• Halophiles
• Halobacterium salinarium
• Most studied halophile
• Photoheterotroph
• Lacks photosynthetic pigments
• Uses bacteriorhodopsins to establish proton
gradient

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Survey of Archaea
• Methanogens
• Largest group of archaea
• Convert carbon dioxide, hydrogen gas, and organic acids to
methane gas
• Convert organic wastes in pond, lake, and ocean sediments to
methane
• Some live in colons of animals
• One of primary sources of environmental methane
• Produced ~10 trillion tons of methane buried on ocean floor
• Digest sludge during sewage treatment

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Survey of Archaea
• Tell Me Why
• Why did scientists formerly think archaea were a type of
bacteria?

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Survey of Bacteria
• Deeply Branching and Phototrophic Bacteria
• Deeply branching bacteria
• Scientists believe these organisms are similar to earliest bacteria
• Autotrophic
• Live in habitats similar to those thought to exist on early Earth
• Aquifex
• Considered to represent earliest branch of bacteria
• Deinococcus
• Has outer membrane similar to Gram-negatives but stains
Gram-positive

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Survey of Bacteria
• Deeply Branching and Phototrophic Bacteria
• Phototrophic bacteria
• Phototrophs that contain photosynthetic lamellae
• Autotrophic
• Divided into five groups based on pigments and source of
electrons for photosynthesis
• Blue-green bacteria (cyanobacteria)
• Green sulfur bacteria
• Green nonsulfur bacteria
• Purple sulfur bacteria
• Purple nonsulfur bacteria

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Vegetative
cell
Heterocyst
Akinete
Sheath
(glycocalyx)
Figure 11.14 Examples of cyanobacteria with different growth habits.

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Figure 11.15 Deposits of sulfur within purple sulfur bacteria.

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Photosynthesis: Comparing Prokaryotes and
Eukaryotes

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• G + C content below 50%
• Have similar 16S rRNA sequences
• Classified in phylum Firmicutes
• Rod-shaped, obligate anaerobes

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Clostridia
• Rod-shaped, obligate anaerobes
• Important in medicine and industry
• Produce toxins that cause diseases in humans
• Endospores survive harsh conditions
• Related microbes include Epulopiscium, sulfate-reducing
microbes, and Selenomonas

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Mycoplasmas
• Facultative or obligate anaerobes
• Lack cell walls
• Smallest free-living cells
• Colonize mucous membranes of the respiratory and
urinary tracts of animals

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Figure 11.16 The distinctive "fried egg" appearance of Mycoplasma colonies.

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Other low G + C bacilli and cocci
• Bacillus
• Endospore-forming aerobes and facultative anaerobes
• Many common in soil
• Bacillus thuringiensis toxin is used by farmers and
gardeners as an insecticide
• Bacillus anthracis causes anthrax
• Other species synthesize antibiotics

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Bt toxin Bacillus thuringiensis
Figure 11.17 Crystals of Bt toxin, produced by the endospore-forming Bacillus thuringiensis.

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Other low G + C bacilli and cocci
• Listeria
• Contaminates milk and meat products
• Capable of reproducing under refrigeration
• Survives inside phagocytic white blood cells
• Rarely causes disease in adults
• In pregnant women, can kill the fetus if crosses the
placenta

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Other low G + C bacilli and cocci
• Lactobacillus
• Grows in the human mouth, stomach, intestinal tract,
and vagina
• Rarely causes disease
• Inhibits the growth of pathogens within the body
• Used in the production of various foods

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Survey of Bacteria
• Low G + C Gram-Positive Bacteria
• Other low G + C bacilli and cocci
• Streptococcus and Enterococcus
• Cause numerous diseases
• Various strains of multi-drug-resistant streptococci
• Staphylococcus
• One of the most common inhabitants of humans
• Produces toxins and enzymes that contribute to
disease

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Survey of Bacteria
• High G + C Gram-Positive Bacteria
• Corynebacterium
• Pleomorphic aerobes and facultative anaerobes
• Produces metachromatic granules
• Mycobacterium
• Aerobic rods that sometimes form filaments
• Slow growth, partly due to mycolic acid in its cell walls
• Some species are pathogens of animals and humans

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Survey of Bacteria
• High G + C Gram-Positive Bacteria
• Actinomycetes
• Form branching filaments resembling fungi
• Cause disease primarily in immunocompromised patients
• Important genera include Actinomyces, Nocardia,
Streptomyces

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Spores
Figure 11.18 The branching filaments of actinomycetes.

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Survey of Bacteria
• High G + C Gram-Positive Bacteria
• Actinomycetes
• Actinomyces
• Normally present in oral cavity and throats of humans
• Nocardia
• Soil- and water-dwelling aerobes
• Can degrade a variety of pollutants
• Streptomyces
• Recycles nutrients in the soil
• Produces most of the important antibiotics

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Largest and most diverse group of bacteria
• Five classes of proteobacteria
• Alphaproteobacteria
• Betaproteobacteria
• Gammaproteobacteria
• Deltaproteobacteria
• Epsilonproteobacteria

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Often capable of growing at low nutrient levels
• Some species have extensions called prosthecae
• Used for attachment and nutrient absorption

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Figure 11.19 A prostheca.
Flagellum Prostheca

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Nitrogen fixers
• Two genera important to agriculture
• Grow in association with the roots of plants
• Azospirillum
• Produces chemicals that aid in nutrient uptake
• Rhizobium
• Produces ammonia, which aids in plant growth

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Figure 11.20 Nodules on pea plant roots.

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Nitrogen fixers
• Rhodopseudomonas palustris
• Reduces hydrogen to hydrogen gas (H2)
• Potential for use as a biofuel

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Nitrifying bacteria
• Oxidation of nitrogenous compounds provides
electrons
• Important in the environment and agriculture
• Convert reduced nitrogenous compounds into nitrate
(nitrification)
• Nitrobacter

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Purple nonsulfur phototrophs
• Grow at the bottom of lakes and ponds
• Use bacteriochlorophylls to harvest light energy
• Do not generate oxygen during photosynthesis

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Pathogenic alphaproteobacteria
• Rickettsia
• Transmitted through bite of an arthropod
• Causes several human diseases
• Brucella
• Causes brucellosis
• Survives phagocytosis by white blood cells

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Alphaproteobacteria
• Other alphaproteobacteria
• Important in industry and the environment
• Acetobacter and Gluconobacter are used in vinegar
production
• Caulobacter inhabits nutrient-poor waters
• Agrobacterium plasmid useful for genetic manipulation
of plants

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Rock or other substrate
Prostheca
Flagellum
Swarmer cell
Cell doubles in size
or
Rosette
1
2
3 4a
4b
Figure 11.21 Growth and reproduction of Caulobacter.

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Figure 11.22 A plant gall.

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Betaproteobacteria
• Pathogenic betaproteobacteria
• Neisseria
• Inhabits mucous membranes of mammals
• Causes numerous diseases
• Bordetella
• Causes pertussis
• Burkholderia
• Colonizes moist environmental surfaces and
respiratory passages of cystic fibrosis patients

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Betaproteobacteria
• Other betaproteobacteria
• Thiobacillus
• Recycles sulfur in the environment
• Zoogloea
• Form flocs that assist in the treatment of sewage
• Sphaerotilus
• Flocs impede flow of waste in treatment plants

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Largest and most diverse class of proteobacteria
• Divided into subgroups
• Purple sulfur bacteria
• Intracellular pathogens
• Methane oxidizers
• Glycolytic facultative anaerobes
• Pseudomonads

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Purple sulfur bacteria
• Obligate anaerobes
• Oxidize hydrogen sulfide to sulfur
• Found in sulfur-rich zones in lakes, bogs, and oceans

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Figure 11.23 Purple sulfur bacteria.

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Intracellular pathogens
• Legionella
• Causes Legionnaires' disease
• Coxiella
• Causes Q fever
• Both pathogens survive within white blood cells

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Methane oxidizers
• Use methane as a carbon and energy source
• Inhabit anaerobic environments
• Digest methane within local environment before it can
impact climate

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Glycolytic facultative anaerobes
• Largest group of gammaproteobacteria
• Catabolize carbohydrates by glycolysis and the
pentose phosphate pathway
• Divided into three families

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Gammaproteobacteria
• Pseudomonads
• Break down numerous organic compounds
• Important pathogens of humans and animals
• Pseudomonas causes infections of the urinary
tract, ear, and lung
• Azotobacter and Azomonas are nonpathogenic soil-
dwelling pseudomonads

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Figure 11.24 Pseudomonas is distinguished by its polar flagella.

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Deltaproteobacteria
• Desulfovibrio
• Recycles sulfur in the environment
• Contributes to the corrosion of iron pipes
• Bdellovibrio
• Destroys other Gram-negative bacteria
• Myxobacteria
• Produce differentiated reproductive structures

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Figure 11.25 Bdellovibrio, a Gram-negative pathogen of other Gram-negative bacteria.
Bdellovibrio
Gram-negative
bacterial prey
Outer
membrane
Periplasmic
space
Cytoplasmic
membrane
10 seconds
later
20 minutes
later
150–210
minutes later
20 minutes
later
10 minutes
1
2
3
4
5

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Binary
fission
(nutrients
plentiful)
Vegetative cells
Slime trail
Myxospores germinate
to form vegetative
cells once nutrients
are restored
Myxospores
Myxospores
Sporangium Mound of cells
Formation of fruiting body
Fruiting body
Mounding when
nutrients are
depleted
Sporangium
5
4
3
2
1
Figure 11.26 Life cycle of myxobacteria.

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Survey of Bacteria
• Gram-Negative Proteobacteria
• Epsilonproteobacteria
• Campylobacter
• Causes blood poisoning and intestinal inflammation
• Helicobacter
• Causes ulcers

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Survey of Bacteria
• Other Gram-Negative Bacteria
• Chlamydias
• Grow intracellularly in mammals, birds, and some
invertebrates
• Some are smaller than viruses
• Most common sexually transmitted bacteria in the
United States

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Survey of Bacteria
• Other Gram-Negative Bacteria
• Spirochetes
• Motile bacteria that move in a corkscrew motion
• Have diverse metabolism and habitats
• Treponema and Borrelia both cause disease in humans

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Survey of Bacteria
• Other Gram-Negative Bacteria
• Bacteroids
• Bacteroides
• Inhabits digestive tracts of humans and animals
• Some species cause infections
• Cytophaga
• Aquatic, gliding bacteria
• Important in the degradation of raw sewage

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Survey of Bacteria
• Tell Me Why
• Why are bacteria all in the same domain (Bacteria)
despite their widely divergent oxygen tolerance, sizes,
shapes, and nutritional requirements?

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Important topics
• Archaea characteristics
• Endospore former bacteria (clostridia, bacillus) and their related
diseases
• Mycoplasma
• Streptococcus
• Staphylococcus
• Helicobacter
• STD causing bacteria
• Prosthecae
• Lipid A