Chapter 13: Evolution and Diversity Among the Microbes

Bacteria, archaea, protists, and viruses: the unseen world

Lectures by Mark Manteuffel, St. Louis Community College

Learning Objectives Know there are microbes in all three domains Know that bacteria may be the most diverse of

all organisms Know that archaea exploit some of the most

extreme habitats Know that protists are single-celled eukaryotes Know that viruses are at the border between

living and non-living Know the highlighted examples of organisms

within each domain.

13.1 Microbes are the simplest, but most successful organisms on earth.• Bacterial fermentation is

used to produce cheese, yogurt, buttermilk, and many types of sausage.

• Cyanobacteria can photosynthesize!

• Nitrogen-fixing bacteria play a symbiotic role helping plants.

Microbes Are Genetically Diverse

>500,000 kinds Millions more expected to be

distinguished! • The number of bacteria in one human’s mouth is greater than the total number of people who ever lived.

• The number of bacteria in a cubic centimeter of soil rivals the number of stars in the galaxy.

Microbes are abundant!

Microbes Can Live Almost Anywhere and Eat Almost

Anything

Bacteria and Archaea are both prokaryotes.

Recall prokaryotic cells.

Bacteria come in 3 basic shapes.

Bacterial Diversity and Movement

Species of bacteria can be distinguished by the sizes, shapes, and colors of the colonies they form and by using gram stain to dye the cell walls.

13.4 Bacterial growth and reproduction is fast and efficient.

Recall Binary fission – asexual reproduction

Bacteria Carry Genetic Information in Two Structures

1) A circular DNA molecule called the chromosome (1 or more)

2) Circular DNA molecules called plasmids

• metabolic plasmids • resistance plasmids • virulence plasmids

Do bacteria have sex?

13.5 Many bacteria are beneficial.

You Owe Your Life to Bacteria Your normal flora

• benign bacteria that is your first line of defense against infection by harmful bacteria

• A disease-causing bacterium must colonize your body before it can make you sick, and your body is already covered with harmless bacteria.

• If the population of harmless bacteria is dense enough, it will stop invading bacteria.

Probiotic therapy • a method of treating infections by deliberately

introducing benign bacteria

13.6 Metabolic diversity among the bacteria is extreme.

Photoautotrophs and the Oxygen Revolution

13.7 Bacteria cause many human diseases.

Pathogenic Bacteria

• Lyme disease and education:

– Is caused by bacteria carried by ticks.

– Antibiotics can cure the disease if administered within a month after exposure.

– If untreated, Lyme disease can cause arthritis, heart disease and nervous disorders.

– The best defense is a public education about avoiding tick bites and seeking treatment.

Figure 15.15

13.8 Bacteria evolve drug resistance quickly.

How?

Rapid reproduction

Misuse and abuse of antibiotics

Excessive use of antibiotics in medicine and agriculture has made several pathogenic bacteria resistant to every antibiotic, and infections caused by these bacteria are nearly impossible to treat.

13.10 Archaea thrive in habitats too extreme for most other organisms.

Extremophiles:– Halophiles thrive in

salty environments.– Acidophiles thrive in

acid environments.– Thermophiles love

extreme heat.– Methanogens thrive

without oxygen and give off methane.

Prokaryotes and Chemical Recycling

– Prokaryotes are important in the breakdown of organic wastes and dead organisms and cycling of chemicals into the air and soil.

Prokaryotes and Bioremediation• Bioremediation is the use of organisms to

remove pollutants from water, air, and soil.– A familiar example is use of prokaryotic

decomposers in sewage treatment.– Also used to clean up oil spills.

In this trickling filter system, bacteria and fungi growing on the rocks remove much of the organic material dissolved in sewage sludge.

Enormous Potential for Industries: Bioremediation

Degrade hydrocarbon Clearing mineral deposits from pipes

in the cooling systems of power plants

13.12 The first Eukaryotes were protists.

Ancient protists

13.13 There are animal-like protists, fungus-like protists, and plant-like protists.

Animal-like Protists

Propel themselves

Appear to hunt for prey

Paramecia

The Ciliates have animal-like qualities.

Protists That Resemble Fungi

Slime molds

Establish multicellular sheet-like colonies on surfaces

Oozing masses of gooey material that flow, engulfing bacteria, fungi, and small bits of organic material as they go

Slime molds resemble fungi in both appearance and function.

Plant-like Protists

Grow in water and resemble plants

Include brown algae

Also called seaweeds

Some protists resemble both plants and animals.

Diatoms

• The evolutionary link between unicellular and multicellular organisms were probably colonial protists.

Figure 15.24

Unicellular protist

Colony

Locomotor cells

Food-synthesizing cells

Early multicellular organism with specialized, interdependent cells

Gamete

Somaticcells

Later organism with gametes and somatic (non-reproductive) cells

1

2

3

Seaweeds– Are large, multicellular marine algae– Grow on rocky shores and just offshore– Are often edible

(a) Green algae

(b) Red algae

(c) Brown algae

13.14 Some protists can make you very sick.

Recall the heterozygous defense against malaria…

13.15 Viruses are not exactly living organisms.

A virus is not alive, but it can carry out some of the same functions as living organisms, provided that it can get inside a cell.

13.16 Viruses are responsible for many health problems.

Why do flu viruses change quickly?

DNA vs. RNA viruses:RNA replication doesn’t involve as much editing as DNA replication. RNA viruses are continually mutating.

Bird Flu (H5N1)

So far requires close contact with infected flocks of birds or by eating birds that had died of the virus.

WHO and national health agencies are preparing for a worldwide pandemic.

A new flu is making headlines.

What role does a pig play in the transmission of virus from a bird to a human?

The cells of pigs have glycoproteins that allow both human and bird viruses to bind to them. If human and bird flu mix, the new strain could be passed from human to human.

Swine Flu (H1N1)

Swine flu does spread easily from human to human, but it is not as lethal as the bird flu.

Pig virus + bird flu virus might produce a new form of the virus that carries the genes that make the bird flu lethal to humans AND the gene that codes for the host-entry glycoprotein (human to human transmission).