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Chapter 11
Characterizing and Classifying Prokaryotes
General Characteristics of Prokaryotic Organisms
Most diverse group of cellular microbes
Thrive in various habitats
Only a few capable of colonizing humans and causing disease
Typical prokaryotic morphologies
Figure 11.1
Endospores
Produced by Gram-positive bacteria Bacillus and Clostridium
Gram- negative bacteria not known to form endospores
Each vegetative cell transforms into one endospore
Each endospore germinates to form one vegetative cell
Defensive strategy against unfavorable conditions
Concern to food processors, health care professionals, and
governments
Locations of endospores
Endospores
Endospore
Figure 11.2
Reproduction of Prokaryotic Cells
All reproduce asexually
Three main methods
Binary fission (most common)
Snapping division
Budding
Binary fission
1 Cell replicates its DNA.
Nucleoid
Cell wall
Cytoplasmic
membrane
Replicated
DNA
2 The cytoplasmic
membrane elongates,
separating DNA
molecules.
3 Cross wall forms;
membrane
invaginates.
4 Cross wall forms
completely.
5 Daughter cells
may separate.
Figure 11.3
Spores of Actinomycetes
Spores
Figure 11.5
Filamentous
vegetative cells
Budding
Figure 11.6
Viviparity
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
Esther R. Angert: 3, 214-224 (March 2005)
Arrangements of Prokaryotic cells
Result from two aspects of division during binary fission
Planes in which cells divide
Separation of daughter cells
Arrangements of cocci and bacilli
Plane of division
Diplococci
Single bacillus
Streptococci
Diplobacilli
Tetrads
Streptobacilli
Sarcinae
Staphylococci
Palisade
V-shape
Figure 11.7
Figure 11.8
Modern Prokaryotic Classification
Currently based on genetic relatedness of rRNA sequences
Three domains
Archaea
Bacteria
Eukarya
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
Figure 11.10 Archaea.
Extremophiles
Require extreme conditions to survive
Temperature, pH, and/or salinity
Prominent members are thermophiles and halophiles
Thermophiles
DNA, RNA, cytoplasmic membranes, and proteins do not function
properly below 45ºC
Hyperthermophiles – require temperatures over 80ºC
Two representative genera
Geogemma
Pyrodictium
Figure 11.11
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
Figure 11.12
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
Have produced ~10 trillion tons of methane that is buried in mud on
ocean floor
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
Cyanobacteria & Purple Sulfur bacteria
Vegetative
cell
Heterocyst
Akinete
Sheath
(glycocalyx)
Sulfur deposits
Figure 11.13
Mycoplasmas
Low G + C Gram-Positive Bacteria
Facultative or obligate anaerobes
Lack cell walls
Smallest free-living cells
Colonize mucous membranes of
the respiratory and urinary tracts
Figure 11.15
High G + C Gram-Positive Bacteria
Corynebacterium
Pleomorphic aerobes and facultative anaerobes
Produces metachromatic (volutin) granules
Mycobacterium
Aerobic rods that sometimes form filaments
Slow growth partly due to mycolic acid in its cell walls
Actinomycetes
Form branching filaments resembling fungi
Important genera include Actinomyces, Nocardia, Streptomyces
Pleomorphism
Variation in cell shape and size
within a single species
(pleomorphic)
Corynebacterium diphteriae
noted for pleomorphism
what are metachromatic
granules? Volutin granules
Inorganic polyphosphate
granules
Appear red when stained with
methylene blue
www.cdc.gov
The branching filaments of actinomycetes
Spores
Figure 11.17
Unusual forms of medically significant bacteria
Rickettsias
• Obligate intracellular parasites
Very tiny, Gram-negative bacteria
Most are pathogens
Cannot survive or multiply outside of
a host cell
Rickettsia rickettisii – Rocky
Mountain spotted fever
Transmitted by ticks and fleas
http://www.ncbi.nlm.nih.gov/books/NBK7624/
http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-3-infectious-diseases-related-to-travel/rickettsial-spotted-and-typhus-fevers-and-relatedinfections-anaplasmosis-and-ehrlichiosis
The rash in a case of Rocky Mountain spotted fever
Figure 21.3
Unusual forms of medically significant bacteria
Chlamydias
Tiny, Obligate intracellular parasites, Gram-negative bacteria
Not transmitted by arthropods
Chlamydia trachomatis – severe eye infection and one of the most
common sexually transmitted diseases (Lymphogranuloma venereum)
Chlamydia pneumoniae – lung infections
Chlamydia psittaci - psittacosis (parrot fever) is a zoonotic infectious
disease contracted from parrots
http://www.cdc.gov/std/chlamydia/
HeLa cells infected with Clamydia trachomatis
Suchland R J et al. Infect. Immun. 2000;68:360-367
Chlamydia trachomatis
Lymphogranuloma venereum
Initial genital lesion is followed by
formation of buboes
Some develop genital sores, urethral
constriction, and genital elephantiasis
Most infections in women are
asymptomatic
Reinfection may cause pelvic
inflammatory disease
Nongonococcal urethritis
Proctitis
Figure 21.7
Chlamydia trachomatis
Trachoma (Ocular disease)
Leading cause of non-traumatic blindness in humans
Scarring of the conjunctiva causes the eyelashes to turn
Causes corneal abrasions that lead to blindness
Infection typically occurs during childbirth
Figure 21.8
Chlamydia psittaci
Ornithosis -Disease of bird that can be transmitted to humans
Usually causes flulike symptoms
Transmitted via inhalation of aerosols or contact with infected
material or a pet bird
Diagnosis difficult, since symptoms similar to other respiratory
infections
Treat with tetracycline or azithromycin