28.1 The Microbial World Chapter 28

1

Chapter 28Microbiology

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28.1 The Microbial World

• Antonie van Leeuwenhoek (1632–1723)

improved microscope in 1600s

– Described “animacules”

– Believed in spontaneous generation

• Louis Pasteur used microbes to discredit the

theory of spontaneous generation in 1659

Pasteur’s Experiments

FIRST EXPERIMENT

flasks outside building

opened briefly

89% show growth

32% show growth

flasks inside building

opened briefly

boiling to

sterilize

broth

boiling to

sterilize

broth


Pasteur’s Experiments

SECOND EXPERIMENT

boiling to

sterilize

broth

flask is open to air

air here is pure

air enter shere

bacteria collect here

100% have no growth


28.1 The Microbial World

• Microbiology– Study of bacteria, archaea, protists, fungi, viruses,

viroids and prions

• Many microbes provide important benefits– Normal microflora on our bodies

– Ecosystems• Decomposers (bacteria and fungi)

• Photosynthesis

– Industry• Food processing

• Medicine

• Biotechnology

28.2 Bacteria and Archaea

• Domain Bacteria and Domain Archaea

– Molecular and cellular differences separate

the two

• Both are prokaryotes

– Do not have nuclei or the membrane-bound

cytoplasmic organelles found in eukaryotic

cells


• Biology of Bacteria

– Most between 0.2-10!m in size

– 3 basic shapes

• Rod (bacillus, pl., bacilli); spherical (coccus, pl.,

cocci); and spiral-shaped or helical

– All have a plasma membrane

– Most have a cell wall



• Biology of Bacteria

– Most bacteria have a single circular

chromosome

• Many also have plasmids

– Accessory rings of DNA

– Ribosomes

– Motile bacteria have flagella


fimbriae flagellumnucleoidchromosome

(DNA)

storage

granule

capsule ribosomes cell wall plasma

membrane


• Bacterial Reproduction

– Reproduce asexually

– Binary fission

• Bacterial cell replicates its genome and divides in

half

• Each daughter cell is a clone – exact copy

– In harsh conditions, some bacteria can form a

resistant endospore

Binary FissionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

cytoplasm

b.

a.

chromosome

cell wall

nucleoid

0.5 !m

b: © CNRI/SPL/Photo Researchers, Inc.


• Bacterial Reproduction

– No sexual reproduction

– 3 mechanisms of genetic recombination

• Conjugation: donor cell passes DNA to a recipient

cell by way of a sex pilus

• Transformation: bacterium takes up DNA fromenvironment released by dead bacteria

• Transduction: viruses carry bacterial DNA fromcell to cell


• Bacterial Metabolism

– Most are heterotrophic

• Require an outside source of organic compounds

– Some are chemoautotrophs

• Reduce carbon dioxide to an organic compound

using energy from chemicals such as ammonia,

hydrogen gas or hydrogen sulfide

– Some are photosynthetic

• Cyanobacteria - have chlorophyll


• Bacterial Diseases in Humans

– Most bacteria do not cause diseases!



– Streptococcus Infections

• Cause more disease than any other bacteria

• Streptococcus pneumoniae: pneumonia, meningitis, and

middle ear infections

• Streptococcus mutans: contributes to tooth decay

• Streptococcus pyogenes: causes the most diseases of any

strep

– Pharyngitis: commonly called strep throat

– Impetigo in infants: mild skin disease

– Scarlet fever: strain produces red rash

– Rheumatic fever: from endotoxins

– Necrotizing fasciitis: “flesh-eating” bacteria



– Staphylococcus aureus and MRSA

• About 20% of people are carriers on their skin

without symptoms

• Disease usually limited to skin infections

• A strain resistant to methicilin is called MRSA

– Killing young, otherwise healthy individuals

– Often posses genes coding for toxins not found in other

S. aureus strains


• Bacterial Diseases

– Tuberculosis (TB)

• Leading cause of death

worldwide due to

infectious 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

© Leonard V. Crowley, An Introduction to Human Disease: Pathology and Pathophysiology

Correlations 5/e, page 383 right and page 385 left; 2001: Jones and Bartlett Publishers,

Sudbury, MA. Reprinted with permission


a. b. 1 mm

tubercle


• Bacterial Diseases in Humans– Food Poisoning

• Bacteria cause food poisoning by two methods

– Produce a toxin while growing in food

» Causes vomiting and diarrhea, usually self-limiting

» Clostridium botulinum – produces one of themost toxic substances on Earth

– Cause an infection while growing in theintestines

• Salmonella



– Drug Control of Bacterial Diseases

• Antibiotics inhibit bacteria by interfering with

unique metabolic pathways

– Not effective against viruses

• Problems related to antibiotic therapy

– Potentially fatal allergic reactions

– Killing off of normal flora

– Bacterial resistance


• Biology of Archaea

– Archaea are more closely related to Eukarya than

bacteria

– Many inhabit extreme environments

• Extreme thermoacidophiles: live in habitats with high

temperature and low pH

• Methanogens: live in anaerobic environments

• Halophiles: live in salty habitats


• Archaeal Structure

– 0.1-15 !m in size

– DNA genome is a single, closed circular molecule

– Plasma membrane of archaea differs markedly from

those of bacteria and eukaryotes

• Single lipid layer branched side chains

– Chemical characteristics make them acid and heat

tolerant

– Reproduce asexually by binary fission

28.3 Protists

• Protists are eukaryotes

– Contain a nucleus and membranous

organelles

• Generally microscopic and unicellular

• Best definition is they are not a plant,

animal, or fungus

• Fungi, plants, and animals all trace their

ancestry to a protist

28.3 Protists

• Biology of Protists

– Can be unicellular, colonial, or multicellular

– Structurally diverse

– May have cell wall or shell

– May have organelles not found in other eukaryotes

– Most carry out asexual reproduction

• Under unfavorable conditions sexual reproduction may be an

option

• May form spores

• May have complicated life cycles

28.3 Protists

• Diversity of Protists

– Traditionally classified by their source of

energy and nutrients

• Algae are photosynthetic

• Protozoans are heterotrophic by ingestion

• Water molds and slime molds heterotrophic by

absorption

– Newer genetic sequence information has

resulted in controversy

• Use 6 groups according to major shared

characteristics


Alg

ae

Pro

tozo

a

Unicellular

eukaryotic

ancestor

Fu

ng

uslike

pro

tists

Photosynthetic protists

Flagellates

Ciliates

Amoeboids

Sporozoans

Water molds

and slime molds

28.3 Protists

• Photosynthetic Protists (Algae)

– Size ranges from unicellular types about the size of

bacteria to multicellular forms 100 feet long (“seaweeds”)

– 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

– Diatoms

• Most numerous unicellular algae in the oceans

• Variety of elaborate shells made of silica

– Dinoflagellates

• Best known for causing red tide

– Produces potent toxin that accumulates in shellfish

28.3 Protists

• Protozoa

– Flagellates

– Ciliates

– Amoeboids

– Sporozoans

• Trypanosoma brucei

– Cause of African sleeping

sickness is transmitted by the

tsetse fly

– Attacks the patient’s blood,

causing inflammation that

decreases oxygen flow to the

brain


a.

b.

flagellum

undulating membrane

trypanosome

red blood cell

a: © Eye of Science/Photo Researchers, Inc.

28.3 Protists

• Sporozoans

– Malaria

• Most widespread and dangerous sporozoan

disease

• Caused by one of several Plasmodium species

• Spread by mosquitoes

– Other sporozoan diseases

• Toxoplasmosis caused by Toxoplasma

• Gastroenteritis caused by Cryptosporidium

28.3 Protists

• Water Molds– Saprophytic - live off dead matter

– Asexual and sexual reproduction

• Slime Molds– Plasmodial (acellular) slime molds

• Exist as plasmodium - diploid, multinucleated, cytoplasmicmass enveloped by a slime sheath

– Cellular slime molds• Exist as individual amoeboid cells

28.4 Fungi

• Fungi are eukaryotes

• General Characteristics

– Strict heterotrophs

– Release enzymes into environment - digestion

is outside of body

– Most are saprophytic

• Along with bacteria, fungi are important as

decomposers

28.4 Fungi

• Biology of Fungi

– Body of fungus is a mass of individual

filaments called hyphae

– Mass of filaments called a mycelium

– 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

• Fungal Disease of Humans (mycoses)– Athlete’s foot

– Ringworm – not a worm

– Black mold (Stachybotrys chartarum)• Sick building syndrome

– Candidiasis (Candida albicans)• Infections of the vagina or mouth occur when normal flora

disturbed by antibiotics or in immunocompromised patients

28.4 Fungi• Diversity of Fungi

– Traditionally classified based on their mode of

sexual reproductionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

common ancestor

common

ancestor

Club fungi

Sac fungi

AM fungi

Zygospore fungi

Chytrids


fertilization

zygospore

meiosisSexual

Asexual

sporangium

mycelium

+ strain

– strain

© Runk/Schoenberger/Grant Heilman Photography

Rhizopus stolonifer

“black bread mold”

28.4 Fungi

• Sac Fungi (phylum Ascomycota)

– Cup fungi, morels, and truffles

– Most fungal pathogens – powdery mildew,

chestnut blight, Dutch elm disease

– Penicillium

• Original source of antibiotic penicillin

• Used to make blue cheese

– Yeasts – unicellular sac fungi

• Saccharomyces cerevisiae – brewer’s yeast

28.4 Fungi

• Club Fungi

– Characteristic sexual reproductive structure is

called a basidium

• Contained within a basidiocarp

– Edible part of a mushroom is the basidiocarp

– Amanitas phalloides, also known as the death

cap, causes 90% of fatalities related to

mushroom poisoning

Sexual Reproduction in Club FungiCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

basidiocarp

fusion meiosis

a. Sexual reproduction

spores

nuclei in

basidium

gill of

mushroom

+!

• Club Fungi

– Smuts and rusts parasitize cereal crops, such as

corn, wheat, oats, and rye

28.4 Fungi

• Lichens - Symbiotic Relationships of Fungi and

Photosynthesizers

• Associations between fungi and cyanobacteria or

green algae

• Can colonize poor soil, rocky surfaces

• Fungi portion offers protection and delivers water

• Photosynthesis gives the fungus nutrients

28.4 Fungi

• Symbiotic Relationships of Fungi

– Mycorrhizal Fungi

• Mutualistic relationships with plant roots

– Helps plants to grow more successfully in poor soils

– Plant provides organic nutrients to the fungus

– Fungus brings water and minerals to the plant

– Found on most plant roots

28.5 Viruses, Viroids, and Prions

• Biology of Viruses

– Viral Structure

• Smaller than bacteria

– 0.03-0.2!m

• Two main components to all viruses

– Capsid (outer portion comprised of proteins)

– Nucleic acid core (DNA or RNA)

– Infect almost every type of organism on earth

– Viruses are specific to a particular host


• 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


• 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

• 10-15% fatality rate in less-developed countries

• MMR vaccine protects against measles (and

mumps and rubella)



– 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

– Varicella-zoster: chickenpox and shingles

– Epstein-Barr virus: infectious mononucleosis



– Antiviral Drugs

• Because viruses use the machinery of host cells

for viral replication, it is difficult to develop drugs

that affect viral replication without harming host

cells

• Antibiotics are not 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


• 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 throughcannibalism

28.1 The Microbial World Chapter 28

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