Ch. 19 Bacteria and Viruses

Ch. 19 Outline

• 19-1: Bacteria– Classifying prokaryotes– Identifying Prokaryotes– Metabolic Diversity– Growth and Reproduction– Importance of Bacteria

Bacteria• Once microscopes were invented, scientists

discovered a world of microorganisms.

• The smallest and most common microorganisms are the prokaryotes, which are single-celled organisms that lack a nucleus

• The word bacteria is so familiar, that we will use it as a common term to describe prokaryotes

Ch. 19 Outline

• 19-2: Viruses– What is a virus?– Viral Infection– Retroviruses– Viruses and Living Cells

• 19-3 Diseases caused by bacteria and viruses– Bacterial Diseases in Humans– Controlling Bacteria– Viral Diseases– Viroids and Prions

Bacteria• Prokaryotes range in size from 1 to 5 micrometers

in diameter. There are exceptions to this rule. The Epulopiscium fisheloni is about 500 micrometers long.

Classifying Prokaryotes• All prokaryotes were once classified in a

single Kingdom named Monera.

• Two Kingdoms of bacteria: Eubacteria, Archaebacteria

• Some scientists think that the Eubacteria and Archaebacteria should be classified as Domains.

Classifying Prokaryotes• Eubacteria: the larger of the two kingdoms

• Some live in fresh water, salt water, land, on and within the human body. They can infect large animals

– Eubacteria cell walls protects the cell from injury and determines its shape

– Eubacteria cell walls contain peptidoglycan, a carbohydrate

– Inside the cell wall, a cell membrane protects the cytoplasm of eubacteria. Some eubacteria have a second cell membrane outside the cell membrane

Classifying Prokaryotes• Archaebacteria are similar to Eubacteria in that

they are equally small, lack nuclei, and have cell walls

• Archaebacteria do not have peptidoglycan in their cell walls, plus they have different membrane lipids

• Also, the DNA sequences of key archaebacteria are more like those of eukaryotes than those of eubacteria

• ****archaebacteria may possibly be ancestors of eukaryotes****

tainano.com

Classifying Prokaryotes• Many archaebacteria live in harsh environments.

One group of arcaheabacteria is the methanogens, that produce methane gas.

• Methanogens Use only CO2, H and N to produce energy to live, and as a result give off methane gas.

• Live in swamps, marshes, gut of cattle, termites, etc. • Methanogens are decomposers

• Other archaebacteria live in extremely salty environments or in hot springs, mud or digestive tracts of animalswww.biology.iupui.edu/.../N100/2k23domain.html

Classifying Prokaryotes

are classified into the kingdoms of

live in harsh environments such as

include a variety of lifestyles such as

Bacteria

Classifying Prokaryotes

are classified into the kingdoms of

live in harsh environments such as

include a variety of lifestyles such as

Bacteria

Eubacteria Archaebacteria

Infecting large

organismsThick mud

Living in soil

Animal digestive

tractsSalty lakes Hot springs

Identifying Prokaryotes: Shapes• Prokaryotes are identified by:

– Their shape– The chemical nature of cell walls– The way they move

Identifying Prokaryotes: ShapesRod-shaped prokaryotes are called bacilli

Spherical shaped prokaryotes are called cocci

Spiral and corked-shaped prokaryotes are called spirilla

Identifying Prokaryotes: Cell Walls• Two different types of cell walls are found in

Eubacteria

• A method called Gram staining is used to tell the two different types of cell walls apart

• Violet stain is used to stain the peptidoglycan cell walls

• Alcohol treatment may wash away the violet stain. If the violet stain remains, then the bacteria are said to be Gram-positive

• These bacteria have thick peptidoglycan cell walls

Identifying Prokaryotes: Cell Walls• Gram-negative bacteria have much thinner

cell walls inside an outer lipid layer

• Alcohol dissolves the lipid and removes the violet stain from the cell walls. The counterstain makes these bacteria appear pink

Identifying Prokaryotes: Cell Walls• What does the type of cell wall have to do with

a bacterium’s resistance to antibiotics?

Gram negative bacteria’s extra layer outside the cell wall can make it hard for some antibiotics to get inside the cell (where they can work).

That makes it important for a doctor to know what kind of bacteria is causing the infection so that most effective antibiotic can be used to treat it.

Identifying Prokaryotes: Movement

• How are the ways prokaryotes move?– Some do not move– Propelled by flagella– Lash snake or spiral forward– Glide

• Which characteristic of prokaryotes illustrates their diversity best?

By the way they obtain energy

Identifying Prokaryotes: Metabolic Diversity

• Which characteristic of prokaryotes illustrates their diversity best? – By the way they obtain energy

• Most prokaryotes are heterotrophs, meaning they get their energy by consuming organic molecules made by organisms

• Other prokaryotes are autotrophs and make their own food from inorganic molecules

Identifying Prokaryotes: Metabolic Diversity

• Most heterotrophic prokaryotes must take in organic molecules for both energy and a source of carbon. These are called chemoheterotrophs.

• Humans are also chemoheterotrophs

• If human food is not handled carefully, bacteria may eat our food and release toxins that cause food poisoning

Identifying Prokaryotes: Metabolic Diversity• Photoautotrophs use light energy to convert carbon

dioxide and water to carbon compounds and oxygen

• Photoautotrophs are found where light is plentiful

• The photoautrophs Cyanobacteria contain a bluish pigment and chlorophyll. They are found everywhere (land, salt and fresh water) and are the first to recolonize an area after a natural disaster.

Identifying Prokaryotes: Metabolic Diversity

• Chemoautotrophs perform chemosynthesis.

• They make organic carbon molecules from carbon dioxide.

Identifying Prokaryotes: Metabolic Diversity• Chemoautotrophs do not require light as a source

of energy. Instead, they use energy directly from chemical reactions involving ammonia, hydrogen sulfide, nitrites, sulfur or iron

• Some live deep in the darkness of the ocean

• They use hydrogen sulfide gas that flows from hydrothermal vents in the ocean

Identifying Prokaryotes: Metabolic Diversity

• Like all organisms, bacteria need a constant supply of energy. This energy is released by the process of cellular respiration or photosynthesis or both

• Organisms that require a constant supply of oxygen to live are called Obligate Aerobes

• Obligate Anerobes DO NOT REQUIRE oxygen and may be killed by it

Clostridium botulinum

Clostridium botulinum

• Obligate Anerobe found in soil

• Gram positive

• Rod-shaped

• Grow in can foods that have not been properly sterilized

• Faculative Anerobes can live with or without oxygen

• Faculative anerobes can live anywhere because they can switch between the processes of cellular respiration or fermentation depending on their environment

Escherichia Coli (E. Coli)

Escherichia Coli (E. Coli)• Faculative anerobe

• Gram negative

• Rod shaped

• Lives anerobically in large intestine

• Lives aerobically in sewage or contaminated water

Escherichia Coli (E. Coli)• Eschericha coli are normal inhabitants of our digestive tract

• A new strain of E. coli (O157:H7) has caused illness and death for people who ate contaminated hamburger meat.

Growth and Reproduction

• Bacteria can not grow and divide indefinitely because of the availability of food and they have to get rid of wastes

• Bacteria grow and divide very rapidly. Their method of division is called binary fission– Bacteria grow until they double in size, copies

DNA and simply splits into two daughter cells– Binary fission is just asexual reproduction

(no exchange of genetic material)

Binary Fission

http://www.swt.edu/~rr33/

Growth and Reproduction

• Conjugation: A process of exchanging genetic info in bacteria

– A hollow bridge forms between two bacterial cells and genes move from one cell to the other

– Increases genetic diversity of bacteria

Growth and Reproduction

• When growth conditions become unfavorable, many bacteria produce spores, which can remain dormant until there are more favorable growth conditions.

– Endospore: one type of spore formed when a bacterium produces a thick internal wall that encloses its DNA and a portion of its cytoplasm.

Importance of Bacteria

• We could not survive without bacteria. Some are producers, others are decomposers, and some are used by humans for various things.

Endospores

Importance of Bacteria• We could not survive without bacteria. Some are

producers, others are decomposers, and some are used by humans for various things.

• Decomposers– Bacteria help recycle nutrients in the environment– Attack and digest dead tissue– Break down complex compounds in sewage to simpler

ones– Produce purified water– Produce nitrogen and carbon dioxide gases– Produce fertilizer compounds

Importance of Bacteria• Nitrogen Fixers

– PLANTS NEED NITROGEN TO MAKE AMINO ACIDS which are used to make PROTEINS

– Plants can not use nitrogen gas (N2) directly. Nitrogen must first be changed chemically to ammonia (NH3) or other nitrogen compounds. The process of converting nitrogen gas to a form that plants can use is called nitrogen fixation.

– Many plants have symbiotic relationships with nitrogen-fixing bacteria. The bacterium Rhizobium, grows on the roots of soybean plants. The plant provides nutrients for Rhizobium, and it converts nitrogen gas in the air to ammonia, which helps the plant.

Importance of Bacteria

• Human Uses of Bacteria– Produce a wide variety of food and beverages– Industry cleaning up oil spills (digest

petroleum)– Mine minerals from the ground– Remove wastes and poisons from water– Synthesize drugs and chemicals (genetic

engineering)– Produce vitamins in human intestines– Produce heat stable enzymes that can be used

in medicine, food production, and industrial chemistry

Ch. 19 Outline• 19-2: Viruses

–What is a virus?

–Viral Infection

–Retroviruses

–Viruses and Living Cells

What is a Virus?

• The word virus is derived from the Latin word for poison

• Dmitri Ivanovski identified the cause of tobacco mosaic disease by extracting juice from an infected plant

• Martinus Beijerinck suggested that tiny particles in the extracted juice caused tobacco mosaic disease (called particles viruses)

• Wendell Stanley inferred that viruses were not alive when he obtained crystals of tobacco mosaic virus

What is a Virus?

• The word virus is derived from the Latin word for poison

• Viruses: particles of nucleic acids, proteins and in some cases, lipids

• Viruses are NON-LIVING, but they do reproduce.

• Viruses can reproduce only by infecting living cells and once inside, they use the machinery of the infected cell to produce more viruses

Viral Structures

A typical virus is composed of a core of DNA or RNA surrounded by a protein coat.

What is a Virus?

• The simplest virus may have only a few genes, whereas the most complex may have more than a hundred genes

• A viruses protein coat is called its capsid. The capsid includes proteins that enable a virus to enter a host cell.

• The capsid proteins of a typical virus bind to receptors on the surface of a cell and “trick” the cell into allowing it inside.

What is a Virus?

• Once inside, the viral genes are expressed. The cell transcribes and translates the viral genetic information into viral capsid proteins

• Sometimes the genetic program causes the host cell to make copies of the virus, and in the process the host cell is destroyed.

What is a Virus?

• Viruses must bind precisely to proteins on the cell surface and then use the host’s genetic system

• Viruses that infect bacteria are called bacteriophages

Viral Infection

• There are two types of viral infections: lytic and lysogenic

• Lytic Infection– The virus enters the cell, makes copies of itself, and

causes the cell to burst (destroyed)

– In a lytic infection, the protein capsid is activated by contact with a specific host cell

– It then injects its DNA directly into the host cell.

– The host cell cannot tell the difference between its own DNA and the DNA of the virus

Viral Infection

– Consequently, the cell begins to make messenger RNA from the genes of the virus

– This viral mRNA is translated into viral proteins that act like a molecular wrecking crew, chopping up the cell DNA, a process that shuts down the infected host cell

– In this lytic infection, the virus then uses the materials of the host cell to make thousands of copies of its own DNA molecule

Viral Infection

– The viral DNA gets assembled into new virus particles

– Before long, the infected cell lyses or bursts, and releases hundreds of virus particles that may go on to infect other cells

– Because the host cell is lysed and DESTROYED, this process is called a lytic infection

Viral Infection

• Lysogenic Infection– A host cell makes copies of the virus

indefinitely

– A virus incorporates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA

– Lysogenic viruses do not lyse the host cell right away. A lysogenic virus remains inactive for a period of time

Viral Infection

– The viral DNA that is embedded in the host’s DNA is called a prophage

– The prophage may remain part of the DNA of the host cell for many generations before it becomes active.

– Eventually, from any number of factors, the DNA of a prophage will be activated. It will remove itself from the host cell DNA and direct the synthesis of new virus particles

Lytic Vs. Lysogenic

Retroviruses• Retroviruses: viruses that have RNA as their

genetic material.

• When a retroviruses infect a cell, they produce a DNA copy of their RNA. This DNA, much like a prophage, is incorporated into the DNA of the host cell.

• There the retrovirus may remain dormant for varying lengths of time before becoming active

Retroviruses• Retroviruses get their name from the fact that

their genetic information is copied backwards, that is from RNA to DNA instead of from DNA to RNA.

• The prefix retro means backwards

• The virus that causes acquired immune deficiency syndrome (AIDS) is a retrovirus and some cancers are caused by retroviruses

Figure 18.9 The structure of HIV, the retrovirus that causes AIDS

Reversetranscriptase

Viral envelope

Capsid

Glycoprotein

RNA(two identicalstrands)

Figure 18.10 The reproductive cycle of HIV, a retrovirus

Vesicles transport theglycoproteins from the ER tothe cell’s plasma membrane.

7

The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER).

6

The double-stranded DNA is incorporatedas a provirus into the cell’s DNA.

4

Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins.

5

Reverse transcriptasecatalyzes the synthesis ofa second DNA strandcomplementary to the first.

3

Reverse transcriptasecatalyzes the synthesis of aDNA strand complementaryto the viral RNA.

2

New viruses budoff from the host cell.9

Capsids areassembled aroundviral genomes and reverse transcriptase molecules.

8

mRNA

RNA genomefor the nextviral generation

Viral RNA

RNA-DNAhybrid

DNA

ChromosomalDNA

NUCLEUSProvirus

HOST CELL

Reverse transcriptase

New HIV leaving a cell

HIV entering a cell

0.25 µm

HIV Membrane of white blood cell

The virus fuses with thecell’s plasma membrane.The capsid proteins areremoved, releasing the viral proteins and RNA.

1

Viruses and Living Cells

• Viruses must infect a living cell in order to grow and reproduce

• Viruses take advantage of the host’s respiration, nutrition, and all other functions and are therefore parasites

• Viruses are not alive because they are not made up of cells and are able to live independently

Viruses and Living Cells• Yet viruses can reproduce, regulate gene

expression and even evolve after infecting living cells

• Viruses are at the borderline of living and non-living things

Viruses and Living Cells

• Viruses were not probably the first living things because they are completely dependent on living things

• Viruses may have evolved from the genetic material of living things

Ch. 19 Outline

• 19-3 Diseases caused by bacteria and viruses

– Bacterial Diseases in Humans

– Controlling Bacteria

– Viral Diseases

– Viroids and Prions

Bacterial Diseases in Humans• Pathogen: disease-causing agents

• Disease can be considered a conflict between the pathogen and the host

• Louis Pasteur was the first scientist to show that bacteria cause a number of human and animal diseases (The Germ Theory)

Bacterial Diseases in Humans

• Bacteria produce disease in one of two ways:

1. Damage the cells and tissue of the infected organism by directly breaking down the cells for food

2. Release toxins (poisons) that travel throughout the body and interfere with normal activity of the host.

• The gram positive bacterium Mycobacterium tuberculosis is inhaled into the lungs where it destroys lung tissue

• If bacterium enters a blood vessel, it may travel to new sights and destroy more tissue

• The Gram positive strain of the Streptococcus bacterium from Group A causes strep throat by releasing toxins into the blood stream

• This infection can also cause damage to the heart valves (rheumatic fever) and kidneys (nephritis). Streptococcal infections can also cause scarlet fever, tonsillitis, pneumonia, sinusitis and ear infections.

• The Gram positive bacterium Corynebacterium diptheria which causes diptheria infects the tissues of the throat and releases toxins into the blood stream

• Diptheria can lead to breathing problems, heart failure, paralysis, and death

Preventing bacterial disease

• Vaccine: preparation of weakened or killed pathogen– Prompts body’s immune system and promts

the body to produce immunity to the disease

– Immunity is the body’s ability to destroy new pathogens

• Antibiotics: compounds that block the growth and reproduction of bacteria

Antibiotics

1. Antibiotic-resistant bacteria – bacteria that have mutated that make them no longer susceptible to the effects of antibiotics

a. Genetic mutations for antibiotic resistance happen spontaneously as a result of errors in DNA replication

b. Taking Antibiotics eliminates the susceptible bacteria from the body and leaves the resistant bacteria, allowing them to reproduce and pass on their genetic traits (bacteria reproduce very rapidly!!!)

Antibiotics

c. Antibiotic misuse:

• Usually, if a full course of an Antibiotic is taken, all the targeted bacteria are killed and there is no chance for a resistant strain to evolve;

• but if the antibiotic is stopped early, the surviving bacteria will be the ones that were most resistant to the antibiotic

Antibiotics

2. There are now strains of tuberculosis and S. aureus that are resistant to multiple drugs = hard to treat! (Multiple Drug Resistant Bacteria)

3. Widespread use of antibacterial soaps can cause antibiotic resistant strains of bacteria to evolve

• Bacillus Anthracis (Anthrax)

• Gram positive• Forms endospores• Found in soil or on the fur

of animals or in their digestive tracts

• Dangerous to humans and animals

• Lung, intestines, and skin• Respiratory difficulties,

fever, diarrhea, rash

Food Poisoning

• Staphylococcus aureus

• Gram positive

• causes the most common type of food poisoning

• painful diarrhea and vomiting

Food Poisoning• Salmonella bacteria

(from unprocessed milk, pork, poultry, eggs)

• Gram negative

• cause vomiting, nausea, and stomach cramps, which can lead to fever and death (especially in the very young or very old)

Bacteria Table

Preventing bacterial disease

• Controlling Bacteria– There are various methods used to control

bacterial growth:• Sterilization kills pathogenic bacteria with heat

• Disinfectants are chemical solution that kills pathogenic bacteria

• Overuse of disinfectants increase the likelihood that common bacteria will eventually evolve to become resistant to them – and therefore much more dangerous and difficult to kill

Preventing bacterial disease

• Controlling Bacteria• Food processing allows storage of food in

refrigerators to prevent (delay) spoilage, or cooking of food at high enough temperatures to kill pathogens

• Canning preserves food for a long time. Food is heated to a high temperature and placed in sterile glass jars or metal containers and sealed. Food that has been properly canned will last almost indefinitely.

• Treating food with everyday chemicals such as salt (salted meat), vinegar (pickled vegetables), or sugar (jam) will preserve food.

Viral Disease in Humans

• Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium.

• Viruses may destroy cells they infect or cause infected cells to alter their growth and development

• Unlike bacteria, viral diseases cannot be treated with antibiotics, but there are some vaccines against viruses. Vaccines should be used before an infection begins

Viral Disease in Humans• Oncogenic or tumor causing viruses may produce

cancer by disrupting the normal controls over cell growth and division– Rous Sarcoma Virus in chickens

– Human Papilloma Virus – genital warts; cervical cancer

Viral Disease in Humans

– Hepatitis B Virus – Liver cancer

– Epstein-Barr Virus – (the virus that causes mono or even chronic fatigue syndrome) – Burkitt’s lymphoma

Viral Disease in Plants

• Plant viruses pose a serious threat to the foods we eat

• Viruses have a hard time entering plant cells because plant cells have a tough cell wall

• Viruses enter plants through tears in leaf tissues, breaks in stems or roots, or microscopic cell wall damage

• Most plant viruses are spread by feeding action of insects

Virus Disease Table

Viroids and Prions• Scientists have discovered two other virus-like particles

that also cause disease: Viroids and Prions

• Viroids cause disease in plants

• Prions cause disease in animals

• Viroids: Single-stranded RNA molecules that have no surrounding capsids– Affect _______ Cells

Viroids and Prions

• Viroids: Single-stranded RNA molecules that have no surrounding capsids

• It is believed that viroids enter an infected cell and direct the synthesis of new viroids

• The viroids then disrupt the metabolism of the plant cell and stunt the growth of the entire plant

Prionsb. Prions – contain no DNA or RNA only protein

i. Disease-causing proteins are folded into the wrong shape, which does not allow it to function as it should.

ii. If a normal prion comes into contact with a disease-causing one, the normal one will also change its shape so that it is folded wrong and no longer functions either; in this way, the disease spreads

iii. Diseases such as Scrapie (sheep), mad cow disease, Creutzfeldt-Jacob disease (in humans) are all prion diseases that can be distributed by eating meat that contains the malfolded prion.

Prions