Transcript Chapter 28 Notes

28.1 The Microbial World
• Bacteria were described as early as the 17th
century
• Louis Pasteur used microbes to discredit the
theory of spontaneous generation in 1659
• Microbiology includes the study of bacteria,
archaea, protists, and some fungi
Pasteur’s Experiments
28.1 The Microbial World
• Many microbes provide important benefits
– Normal flora on our bodies
– Ecosystems
• Decomposers (bacteria and fungi)
• Photosynthesis (cyanobacteria and some protists)
– Industry
• Food processing
• Medicine
• Biotechnology
28.2 Bacteria and Archaea
28.1 The Microbial World
• Typical Bacteria Cell
– Bacteria can be
categorized based on
their cell wall
• Gram positive
• Gram negative
28.2 Bacteria and Archaea
• Bacterial Reproduction
– Binary Fission: a bacterial cell replicates its genome
and divides in half (asexual reproduction)
– In harsh conditions, some bacteria can form a
resistant endospore (not a reproductive strategy)
– No sexual reproduction, but three mechanisms of
genetic recombination
• Conjugation: “male” cell passes DNA to “female” through a
sex pilus
• Transformation: bacterium takes up DNA from environment
released by dead bacteria
• Transduction: viruses carry bacterial DNA from cell to cell
Binary Fission
28.2 Bacteria and Archaea
• Bacterial Metabolism
– Most are Heterotrophic
• Some are anaerobic and cannot use oxygen as final electron
acceptor
– Sulfate reducers-transfer electrons to sulfate
– Denitrifying bacteria use nitrate
– Some are chemosynthetic
• Reduce carbon dioxide to an organic compound using
electrons from ammonia, hydrogen gas, hydrogen sulfide, or
certain minerals such as iron
– Some are photosynthetic
• Cyanobacteria- have chlorophyll
– Other types split hydrogen sulfide instead of water to produce
sulfur as a by-product
Cyanobacteria
28.2 Bacteria and Archaea
• Bacterial Diseases in Humans
– Most bacteria are non-pathogenic
– Disease-causing bacteria have genes that code for
virulence factors
• These genes can be transferred between bacteria
28.2 Bacteria and Archaea
• Bacterial Diseases in Humans
– Streptococcus Infections
• Cause more disease than any other genus
• Pharyngitis: most common and mild strep disease
• Streptococcus pneumoniae: important agent in bacterial
pneumonia
• Streptococcus mutans: contributes to dental caries
• Streptococcus pyogenes: causes the most diseases of any
strep
– Impetigo in infants: mild skin disease
– Rheumatic fever: from endotoxins
– Necrotizing fasciitis: “flesh-eating” bacteria
Streptococcus pyogenes
28.2 Bacteria and Archaea
• Bacterial Diseases
– Tuberculosis
• Highest mortality
worldwide of any disease
• 1/3 of the world’s
population is infected
• Caused by Mycobacterium
tuberculosis
• Active lesions in lung
cause tubercles from
immune response
– Become calcified
28.2 Bacteria and Archaea
• Bacterial Diseases in Humans
– Food Poisoning
• Bacteria cause food poisoning by two methods
– They may cause an infection while growing in the
intestines
» Salmonella
– They may produce a toxin while growing in food
» Staphylococcus
» Clostridium botulinum
28.2 Bacteria and Archaea
• Bacterial Diseases in Humans
– Chlamydia Infections
• Chlamydia trachomatis
– small intracellular parasite that causes a variety of diseases
» Blindness
» Pelvic inflammatory disease (an STD)
28.2 Bacteria and Archaea
• Bacterial Diseases in Humans
– Drug Control of Bacterial Diseases
• Antibiotics
– Inhibit protein synthesis by bacteria
» Ex: Erythromycin and tetracyclins
– Inhibit cell wall biosynthesis
» Penicilins and cephalosporins
• Problems related to antibiotic therapy
– Potentially fatal allergic reactions
– Killing off of normal flora
– Bacterial resistance
28.2 Bacteria and Archaea
• Biology of Archaea
– Archaea are more closely related to Eukarya than bacteria
• Based on nucleic acid similarities
– Inhabit extreme environments
• Extreme thermoacidophiles: live in habitats with high temperature
and low pH
• Methanogens: live in anaerobic environments
• Halophiles: live in salty habitats
28.2 Bacteria and Archaea
• Archaeal Structure
– 0.1-15 microns in size
– DNA genome is a single, closed circular molecule
– Gram-positive archaea have thick polysaccharide cell
wall
– Gram-negative archaea have a protein surface layer
– Cell membranes-single lipid layer which may be
highly branched
– Chemical characteristics make them acid and heat
tolerant
– Reproduce by binary fission
28.2 Bacteria and Archaea
• Archaeal Metabolism
– Some are heterotrophs, some are autotrophs
– Halophiles have a unique photopigment resembling a
pigment in human retina
– Many are obligate anaerobes
• Methanogens reduce carbon dioxide to methane
– Found in swamps, lake sediments, hot springs, and digestive
tracts of animals (especially cows)
– Methane is a greenhouse gas
Extreme Habitats
28.3 Protists
• Domain Eukarya, Kingdom Protista
– Generally microscopic and unicellular
– Most reproduce asexually, but may reproduce
sexually under adverse environmental conditions
• Form spores or cysts to survive unfavorable conditions
– Protists may be grouped according to mode of
nutrition
• Algae: Photosynthetic
• Protozoans: Heterotrophic by ingestion
• Water molds: Heterotrophic by absorption
28.3 Protists
• Biology and Diversity of Algae
– Can be unicellular, colonial, or filamentous
– Size ranges from unicellular types about the size of
bacteria to multicellular forms 100 feet long
(“seaweeds”)
– Algae carry out photosynthesis
– Algae generally have a rigid cell wall
28.3 Protists
• Green Algae
– Closely related to plants as they have some similar
characteristics
• Cell walls contain cellulose
• Have chlorophyll a and b
• Store food as starch
– Representatives of different types of Green Algae
•
•
•
•
Chlamydomonas: unicellular green algae with two flagella
Volvox: a colonial green algae
Spirogyra: a filamentous green algae
Ulva: a multicellular green algae
Representative Green Algae
28.3 Protists
• Diatoms
– Most numerous unicellular
algae in the oceans
– Utilize a brown pigment in
addition to chlorophyll
• Base of many marine food
chains
– Component of
phytoplankton
– Intricate shells of silica
28.3 Protists
• Dinoflagellates
– Have cellulose plates and
two flagella
– Component of
phytoplankton
• Can produce neurotoxin• Responsible for “red tides”
– Generally photosynthetic
– Some have
bioluminescence
28.3 Protists
• Red Algae
– Mainly multicellular
seaweeds
– Contain red and blue
pigments as well as
chlorophyll
– Produce useful gelling
agents
• Agar
• Carageenan
28.3 Protists
• Brown Algae
– Multicellular seaweeds, kelps
– Has accessory pigments
ranging in color from brown to
black
– Sargasso Sea-has large
floating mats of brown algae
– Harvested for food in some
parts of the world
• Also as a source of algingelatinous product used in
foods
28.3 Protists
• Euglenoids
– Freshwater unicellular organisms
– Most have chloroplasts but some do not
– Have two flagella
– Have a photoreceptor called an eyespot
– Plasma membrane is surrounded by a flexible pellicle
• Allows movement
Euglena
28.3 Protists
• Biology and Diversity of Protozoans
– Usually motile eukaryotic unicellular heterotrophic
protists
– Commonly divided and classified by mechanism of
locomotion
– Wide distribution
• Aquatic habitats (zooplankton)
– Many are parasitic
– Variable cell structure
• Some have more than one nucleus
• Contractile vacuoles- regulate water balance
• Some produce cysts for survival in adverse conditions
28.3 Protists
• The Ciliates
– Largest group of
protozoans
– Move by means of cilia
– Cilia aid in prey
capture and feeding
– Examples:
Paramecium and
Stentor
• Amoeboids
– Move by pseudopodia
– Aquatic, freshwater
and saltwater forms
– Component of
zooplankton
– Feed by phagocytosis
– Some cause disease
Ciliates
Amoeboids
28.3 Protists
• Zooflagellates
– Move by flagella
– Most are symbiotic, many
parasitic
• Trypanosoma brucei– Causes African sleeping
sickness
– Tsetse fly is vector
– Lives in bloodstream of
host
• Giardia lamblia– Causes giardiasis
» Severe diarrhea
28.3 Protists
• Sporozoans
– Generally nonmotile with complex life cycles
– Intercellular or intracellular parasites
– Produce resistant spores
– Malaria
• Most widespread and dangerous sporozoan disease
• Caused by Plasmodium vivax• Spread by mosquitoes
28.3 Protists
28.3 Protists
• Toxoplasma gondii
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–
–
–
Causes Toxoplasmosis
Oocysts commonly transmitted by infected cats
For most people, it produces only mild flu-like symptoms
In pregnant women it can infect the fetus and cause neurological
damage
• Cryptosporidium
– Causes mild gastroenteritis in most, but can be fatal in people
who are immunosuppressed
– Passed in feces of infected animals
– Can pass through water filtration processes and is unaffected by
chlorination
28.3 Protists
• Molds as Protists
– Water Molds
• Saprophytic, live off
dead matter
• Have a filamentous
body with cell walls of
cellulose
• Produce flagellated
spores during asexual
reproduction
• During sexual
reproduction, produce
eggs and sperm
• Molds as Protists
– Cellular Slime Molds
• Exist as individual
amoeboid cells
• Common soil
decomposers
• When food is scarce, they
aggregate together to form
a pseudoplasmodium
– This gives rise to
sporangia which
produces spores
– Spores germinate
releasing haploid
amoeboid cells
28.3 Protists
28.4 Fungi
• General Characteristics
– True multicellularity (different types of cells)
– Strict heterotrophs
– Release enzymes into environment- digestion is
extracellular
– Most are saprophytic
– Along with bacteria, fungi are important as
decomposers
28.4 Fungi
• Biology of Fungi
– Body of fungus is a mass of filaments called a mycelium
• Each filament is a hypha
– Some have crosswalls between cells called septa
» Septa have pores that allow fungal cells to exchange components
of the cytoplasm
– Nonseptate fungi lack crosswalls between cells-multinucleate
– Fungal Cell Structure
• Cell walls contain chitin instead of cellulose
• Energy reserve is glycogen like in animal cells
• Fungi are nonmotile
• Move toward food source by growing toward it
28.4 Fungi
• Biology of Fungi
– Fungal Reproduction
• Adapted to dry land
• Produce wind-blown spores
– Haploid reproductive cell germinates and develops into new
mycelium (asexual)
– Sexual reproduction occurs by the conjugation of two different
mating types
» Designated as + and –
» After fusion of nuclei a zygote forms
» The zygote undergoes meiosis
» Produces haploid spores and cycle begins again
28.4 Fungi
• Zygospore fungi (phylum Zygomycota)
– Saprotrophs and parasites
– Rhizopus stolonifer –black bread mold is a familiar zygospore
fungus
28.4 Fungi
• Sac Fungi (phylum Ascomycota)
– Sexual reproductive structure called an ascocarp
– Many sac fungi reproduce by producing chains of
spores called conidia
– Disease-causing sac fungi
• Chestnut blight, Dutch elm disease, Ergot
– Some sac fungi are useful to humans
• Original source of penicillin
• Used to produce blue cheese
• Yeasts are used in the food industry
Reproduction in Sac Fungi
Sexual
Asexual
28.4 Fungi
• Club Fungi
– Phylum Basidiomycota
– Characteristic sexual reproductive structure is called a basidium
• Contained within a basidiocarp
– Edible part of a mushroom is the basidiocarp
– Forms after fusion of + and – hyphae
– Sexual reproduction is most prominent in this group
• Asexual reproduction can occur by asexual spores
Sexual Reproduction in Club Fungi
28.4 Fungi
• Environmental Aspects of Fungi
– Fungi and Photosynthesizers
• Lichens
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–
–
–
–
Associations between fungi and cyanobacteria or green algae
Efficient at acquiring nutrients and moisture
Can colonize poor soil, rocky surfaces
Produce organic matter and create new soil
Three characteristic forms- crustose (compact), foliose
(shrublike), fruticose (leaflike)
– Body of lichen has three layers-fungi form top and bottom
layers and protect middle layer of photosynthetic cells
» Fungi portion offers protection and delivers water
» Photosynthesis gives the fungus nutrients
Lichen Morphology
28.4 Fungi
• Environmental Aspects of Fungi
– Mycorrhizal Fungi
• Mutualistic relationships with plant roots
– Helps plants to grow more successfully in poor soils
• Fungi can live on the outside surface of roots, or it can
penetrate the root tissues
– Plant provides organic nutrients to the fungus
– Fungus brings water and minerals to the plant
» Hyphae provide lots of surface area for water absorption
28.4 Fungi
• Fungal Diseases of
Plants
– Many enter through
the stomata of the
leaves or through a
wound
– Smuts and rusts: sac
fungi that parasitize
cereal crops
28.4 Fungi
• Fungal Disease of Humans (mycoses)
– Tineas
• Caused by moldlike fungi
– Ex: Athlete’s foot
• Ringworm
– Redness and inflammation due to enzymes released by the
fungus; extends outward in a ring-shape
– Histoplasmosis (Histoplasmosis capsulatum)
• Can be transmitted by bird droppings
– May be asymptomatic of mild, flu-like symptoms
– In more serious cases, lesions may form in the lungs which
later become calcified
– Candidiasis (Candida albicans)
• Yeast infections resulting from imbalance of normal flora
28.5 Viruses, Viroids, and Prions
28.4 Fungi
• Control of Fungi
– Fungi more closely resemble animal cells than
bacteria
– Makes it harder to develop antibiotics that will kill
fungi and not the host
– Fungi synthesize steroids differently• Fungicides are directed at steroid biosynthesis
28.5 Viruses, Viroids, and Prions
• Biology of Viruses
– Viral Structure
• Smaller than bacteria
– Viruses are usually smaller than 0.2 microns
– Bacteria are usually longer than 1 micron
• Two main components to all viruses
– Capsid (outer portion comprised of proteins)
» May be surrounded by a lipid envelope
» Spikes may be present for attachment to a host cell
– Nucleic acid core (DNA or RNA)
» Both DNA and RNA may be single or doublestranded, depending on the virus
Viruses
28.5 Viruses, Viroids, and Prions
• Viral Replication
– Viruses are specific to a particular host
• Spikes on a virus configure exactly to receptor molecules on
the membrane of a potential host cell
Life Cycle of an Animal Virus (RNA)
28.5 Viruses, Viroids, and Prions
• Viral Replication
– Latency
• Viral genome of some viruses can lie dormant within host cell
genome
– Called a provirus
– Viral DNA is replicated along with the host genome
– Stress may stimulate provirus to enter biosynthesis stage
• Retroviruses
– Genome is in RNA
– Enzyme reverse transcriptase transcribes RNA into DNA
» This DNA is called cDNA (copy DNA)
– cDNA can incorporate into host cell genome
– Example: Human Immunodeficiency Virus (HIV)
28.5 Viruses, Viroids, and Prions
• Viral Diseases in Humans
– The Common Cold and Influenza
• Colds are caused mainly by rhinoviruses
– Runny nose, mild fever (possible), fatigue
– Lasts around a week
• Flu is caused by influenza viruses
– High fever, chills, body aches, severe fatigue
– Can be fatal
– May last several weeks
• Antigens on cold and flu viruses can change
– Antigenic drift
– Antigenic shift
Antigenic Drift and Antigenic Shift
28.5 Viruses, Viroids, and Prions
• Viral Diseases in Humans
– Measles
• Very contagious human disease
• Spread by respiratory route
• 7-12 day incubation period before flu-like symptoms and rash
appear
• Major killer worldwide in non-vaccinated populations
• MMR vaccine protects against measles
28.5 Viruses, Viroids, and Prions
• Viral Diseases in Humans
– Herpesviruses
• Remain latent much of the time
• Four types of herpesviruses that cause disease in humans
– Herpes simplex type 1: cold sores and fever blisters
– Herpes simplex type 2: genital herpes
– Herpes zoster: chickenpox and shingles
– Epstein-Barr virus: infectious mononucleosis
28.5 Viruses, Viroids, and Prions
• Viral Diseases in Humans
– Antiviral Drugs
• Antibiotics are most effective against viruses
• Some antiviral drugs interfere with viral replication
• Other antiviral drugs may affect virus attachment
• Many times, no drugs are available for viral infections.
28.5 Viruses, Viroids, and Prions
• Viroids and Prions
– Acellular pathogens
• Viroids are naked RNA molecules which do not code for
proteins
– Infect plant cells and cause disease
• Prions are proteinaceous infectious particles
– Normal protein change their shape, this causes other normal
proteins to change their shape
– Causes degenerative diseases of the nervous system
– Prions are passed through ingestion of infected tissues
» Scrapie in sheep
» Mad cow disease in cattle
» Creutzfeld-Jakob disease in humans
» Kuru: human to human transmission through cannibalism