Viruses, Bacteria, Protists, and Fungi

Viruses and Bacteria

Bacteria

• Recall that prokaryotes are unicellular organisms that do not have a nucleus or

membrane-bound organelles.

Diversity of Prokaryotes

• They are classified in two kingdoms—archaebacteria and eubacteria.

• They used to be in one kingdom called Monera.

Diversity of Prokaryotes

• Eubacteria have peptidoglycan (a kind of sugar) in their cell walls and Archaebacteria do not.

• Many biochemical differences exist between these two types of prokaryotes.

• They also have different types of fats in their cell membranes.

• There are three types of archaebacteria that live mainly in extreme habitats where there is usually no free oxygen available.

Archaebacteria: The extremists

• One type of archaebacterium lives in oxygen-free environments and produces methane gas.

• These methane-producing archaebacteria live in marshes, lake sediments, sewage plants and the digestive tracts of some mammals, such as cows.

Archaebacteria: The extremists

• A second type of archaebacterium lives only in water with high concentrations of salt.

Archaebacteria: The extremists

Dead Sea

• A third type lives in the hot, acidic waters of sulfur springs and cracks in the deep ocean.

Archaebacteria: The extremists

• Eubacteria, the other kingdom of prokaryotes, includes those prokaryotes that live in places more hospitable than archaebacteria inhabit and that vary in nutritional needs.

Eubacteria: The heterotrophs

• The heterotrophic eubacteria live almost everywhere and use organic molecules as their food source.

• Some bacterial heterotrophs are parasites, obtaining their nutrients from living organisms.

Eubacteria: The heterotrophs

• Others are saprophytes—organisms that feed on dead organisms or organic wastes.

• A second type of eubacterium is the photosynthetic autotroph.

Eubacteria: Photosynthetic autotrophs

• These eubacteria live in places with sunlight because they need light to make the organic molecules that are their food.

• Cyanobacteria are photosynthetic autotrophs that live in ponds, streams and moist soil.

Eubacteria: Photosynthetic autotrophs

• Most cyanobacteria are blue-green and some are red or yellow in color.

Cyanobacteria

• A third type of eubacterium is the chemosynthetic autotroph.

Eubacteria: Chemosynthetic autotrophs

• Unlike the photosynthetic bacteria, the chemosynthetic bacteria do not obtain the energy they need to make food from sunlight.

Eubacteria: Chemosynthetic autotrophs

• Chemosynthesis: the break down and release of energy in inorganic compounds containing sulfur and nitrogen

What is bacterium?

• A bacterium consists of a very small cell.

• Although tiny, a bacterial cell has all the structures necessary to carry out its life functions.

The structure of bacteria

• Prokaryotic cells have ribosomes, but their ribosomes are smaller than those of

eukaryotes.

• They also have genes that are located for the most part in a single circular chromosome, rather than in paired chromosomes.

A Typical Bacterial Cell• A typical bacterium, such as Escherichia coli would have some or all of the structures shown in this diagram of a bacterial cell.

Capsule Cell WallChromosome

Flagellum

PlasmidPilus

Plasma membrane

The structure of bacteria• A bacterial cell remains intact as long as its cell wall is intact.• If the cell wall is damaged, water will enter the cell by osmosis, causing the cell to burst.• Scientists used a bacterium’s need for an intact cell wall to develop a weapon against bacteria that cause disease.

The structure of bacteria• In 1928, Sir Alexander Fleming accidentally discovered penicillin, the first substance that destroys bacteria—used in humans.

The structure of bacteria

• Later, biologists discovered that penicillin can interfere with the ability of some bacteria to make cell walls.

• When such bacteria grow in penicillin, holes develop in their cell walls, water enters their cells, and they rupture and die.

Identifying bacteria

• One trait that helps categorize bacteria is how they react to Gram stain.

• Gram staining is a technique that distinguishes two groups of bacteria because the stain reflects a basic difference in the composition of bacterial cell walls.

• After staining, Gram-positive bacteria are purple and Gram-negative bacteria are pink.

Gram-positive bacteria Gram-negative bacteria

Identifying bacteria

• Gram-positive bacteria are affected by different antibiotics than those that affect Gram-negative bacteria.

Gram-positive bacteria Gram-negative bacteria

Identifying bacteria

Identifying bacteria• Bacterial cell walls also give bacteria different shapes.

• Shape is another way to categorize bacteria.

•Coccus—spheres• Bacillus—rods•Spirillum–spirals

Identifying bacteria• Bacterial cells grow in patterns that provide another way of categorizing them.• Diplo–grows in pairs.• Staphylo–grows in clusters that resemble grapes.• Strepto–grows in chains of cells.

Reproduction by binary fission

• Bacteria reproduce asexually by a process known as binary fission.

• Binary fission: a process in which one cell divides to form two identical cells•Binary fission is a form of asexual reproduction (involves only one parent).

Reproduction by binary fission

Sexual reproduction• In addition to binary fission, some bacteria

have a form of sexual reproduction that involves two parents• Conjugation: one bacterium transfers all or

part of its chromosome to another cell through or on a bridgelike structure called a pilus that connects the two cells.

Sexual reproduction

• Conjugation results in a bacterium with a new genetic composition.

• This bacterium can then undergo binary fission, producing more cells with the same genetic makeup.

Diversity of metabolism• Modern bacteria have diverse types of

respiration.• Obligate aerobes: require oxygen for respiration

• Obligate anaerobes: are killed by oxygen

A survival mechanism• Some bacteria, when faced with unfavorable environmental conditions, produce endospores.• Endospore: a tiny structure that contains a bacterium’s DNA and a small amount of its cytoplasm, encased by a tough outer covering

that resists drying out, temperature extremes, and harsh chemicals.

A survival mechanism• To kill endospores, items must be

sterilized—heated under high pressure in either a pressure cooker or an autoclave.

A survival mechanism

• This is because the endospores of the bacterium called Clostridium botulinum easily get into foods being canned.

• Canned food must be sterilized and acidified.

A survival mechanism

• Bacteria grow in the anaerobic environment of the can and produce a powerful deadly

poison, called a toxin, as they grow.

• If the endospores of C. botulinum get into improperly sterilized canned food, they germinate.

• This deadly toxin saturates the food and, if eaten, causes the disease called botulism.

A survival mechanism

• B. anthracis causes anthrax, a disease that commonly infects cattle and sheep, but can also infect humans.

• A different bacterium, Bacillus anthracis, lives in the soil.

• Most human anthrax infections are fairly harmless and occur on the skin as a result of handling animals.

The Importance of Bacteria

• Bacteria help to fertilize fields, to recycle nutrients on Earth, and to produce foods and medicines.

• Disease-causing bacteria are few compared with the number of harmless and beneficial bacteria on Earth.

Nitrogen fixation

• Other bacteria then convert the ammonia into nitrite (NO2

–) and nitrate (NO3),which plants can use.

• Nitrogen fixation: process in which some species of bacteria convert N2 into ammonia (NH3)

• Bacteria are the only organisms that can perform these chemical changes.

Nitrogen fixation

• Farmers grow legume crops after the harvesting of crops such as corn, which depletes the soil of nitrogen.

• Some nitrogen-fixing bacteria live symbiotically within the roots of some trees and legumes.

Recycling of nutrients

• This food is passed from one heterotroph to the next in food chains and webs.

• Autotrophic bacteria and also plants and algae, which are at the bottom of the food chains, use the nutrients in the food they make.

• In the process of making food, many autotrophs replenish the supply of oxygen in the atmosphere.

Food and medicines• Some foods that you eat—mellow Swiss cheese, crispy pickles, tangy yogurt—would not exist without bacteria.

Food and medicines

• Specific bacteria are used to make different foods, such as vinegar, cheeses, and

sauerkraut.

• Bacteria also inhabit your intestines and produce vitamins and enzymes that help digest food.

Food and medicines

• Streptomycin, erythromycin, bacitracin, and neomycin are some of these antibiotics.

• In addition to food, some bacteria produce important antibiotics that destroy other types of bacteria.