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  Describe how, in humans, bacteria can have harmful or beneficial health effects

Learning Objectives  Discuss how Archaea exploit some of the most extreme habitats  Describe the protists  Discuss how viruses are at the border between living and non-living

13.1–13.2 There are microbes in all three domains.

13.1 Microbes are the simplest but most successful organisms on earth.

How can a microbe function when its body is just a single cell? Amoeba as an example

How would you decide whether a group of organisms can be considered successful?

Microbes Are Genetically Diverse  >500,000 kinds  Millions more expected to be distinguished!

Microbes Can Live Almost Anywhere and Eat Almost Anything

Microbes are abundant!

Take-home message 13.1  Microbes are simple, but they do everything that multicellular organisms do.  They can live anywhere, from moderate to extreme environments.  There are millions of different kinds of microbes on earth, in enormous numbers.

13.2 Not all microbes are evolutionarily related.

Take-home message 13.2  Microbes are grouped together only because they are small, not because of evolutionary relatedness.  They occur in all three domains of life, and also include the viruses, which are not included in any of the domains.

13.3−13.5 Bacteria may be the most diverse of all organisms.

13.3 What are bacteria?

Take-home message 13.3  Bacteria are efficient single-celled organisms, with an envelope surrounding the cytoplasm, which contains the DNA (they have no nuclei and no intracellular organelles).  Bacterial cells undergo binary fission, and a single cell can grow into a colony of cells.

13.4 Bacterial growth and reproduction is fast and efficient.

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

Would it be useful to be able to transfer genetic information from one adult human to another?

Take-home message 13.4  Bacteria grow rapidly.  They have efficiently organized chromosomes—genes are organized in groups with related functions and virtually all the DNA codes for proteins.

Take-home message 13.4  Bacteria sometimes carry the genes for specialized traits on small DNA molecules called plasmids that can be transferred from one bacterial cell to another by conjugation.  DNA can also be transferred laterally between bacterial cells by transduction or transformation.

13.5 Metabolic diversity among the bacteria is extreme.

Photoautotrophs and the Oxygen Revolution

Take-home message 13.5  Some bacteria eat organic molecules, some eat minerals, and still other bacteria carry out photosynthesis.  About 2.6 billion years ago, the photosynthesizing bacteria were responsible for the first appearance of free oxygen in the Earth's atmosphere.

13.6–13.9 In humans, bacteria can have harmful or beneficial health effects.

13.6 Many bacteria are beneficial

You owe your life to bacteria? Normal flora Probiotic therapy

Take-home message 13.6  Your body fights bacteria with 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 prevent invading bacteria from gaining a foothold.

13.7 Bacteria cause many human diseases. Pathogenic bacteria

Take-home message 13.7  Some bacteria always cause disease and others do no harm except under certain conditions.  For example, Streptococcus pyogenes can be harmless, but under some conditions it releases toxins that are responsible for strep throat, scarlet fever, and necrotizing fasciitis (caused by the flesh-eating strains).

13.8 Bacteria’s resistance to drugs can evolve quickly.

Where do antibiotics come from, and why do they so quickly lose their effectiveness? Chemicals that kill!

Bacteria and other microbes resist antibiotics in a variety of ways:  Pumping antibiotics out of their cell  Proteins that bind to the antibiotic molecule and block its lethal effect

Bacteria and other microbes resist antibiotics in a variety of ways:  Enzymes that break down the antibiotic molecules that are then used as fuel to help the bacteria grow faster

Why is it essential to take every dose of an antibiotic prescribed by a doctor?

Take-home message 13.8  Microbes routinely evolve resistance to antibiotics.  The genes that allow bacteria to combat antibiotics are located on plasmids, and plasmid transfer allows an antibiotic- resistant bacterium to pass that resistance to other bacteria.

Take-home message 13.8  Excessive use of antibiotics in medicine and agriculture has made several pathogenic bacteria resistant to every known antibiotic, and infections caused by these bacteria are nearly impossible to treat.

13.10 Archaea are profoundly different from bacteria.

Additional Differences among Bacteria, Archaea, and Eukarya  Chemical compositions of the plasma membranes, cell walls, and the flagellae  Eukarya have a distinct cell nucleus and a nuclear membrane; bacteria and archaea do not.

Take-home message  Archaea show a set of characteristics that places them between bacteria and eukaryotes on the tree of life.

Take-home message  Archaea and bacteria may look similar, but they have large and significant differences in their DNA sequences, as well as differences in their plasma membranes, cell walls, and flagella.  Furthermore, neither archaea nor bacteria resemble eukarya in one key way: only eukarya have a distinct cell nucleus and nuclear membrane.

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

Extremophiles

Take-home message  Archaeans can tolerate extreme physical and chemical conditions that are impossible for most other living organisms, but they also live in moderate conditions and even in the human intestine.

13.12 Much Archaean diversity has yet to be discovered.

Important applications in bioengineering and environmental remediation Remember Thermus aquaticus?

Enormous Potential for Industries: Bioremediation  Degrade hydrocarbon  Clearing mineral deposits from pipes in the cooling systems of power plants

Take-home message  Archaea are hard to study because many require extreme heat or pressure to grow, and these conditions are not easy to provide in a laboratory.  But the ability of archaea to grow in such extreme conditions makes them potentially valuable for industrial and environmental purposes.

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

13.16–13.19 Viruses are at the border between living and non-living.

13.16 Viruses are not exactly living organisms.

Lytic Cycle Lytic Cycle video

Lysogenic Cycle

Lytic and Lysogenic

Take-home message  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.

Take-home message  A virus takes over the protein-making machinery of the host cell to produce more viral genetic material (RNA or DNA) and more viral protein.  The viral proteins and genetic material are assembled into new virus particles and released from the cell.

13.17 Viruses are responsible for many health problems.

Why do flu viruses change quickly? DNA vs. RNA viruses

Take-home message  Many diseases are caused by viruses.  DNA viruses are relatively stable because DNA replication enzymes check for errors and correct them during replication.

Take-home message  RNA viruses change quickly because RNA replication enzymes do not have error- checking mechanisms.

13.18 Viruses infect a wide range of organisms.

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

Bird Flu  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.

Mixing RNA  Pig + bird flu virus + human 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.

Take-home message  Glycoproteins on the surfaces of viruses determine what cells they can invade.  Most viruses infect just one species, or only a few closely related species, and enter only one kind of cell in that species.

13.19 HIV illustrates the difficulty of controlling infectious viruses.

HIV mutates easily.

HIV Attacks White Blood Cells

The Immune System Collapses  Normally white blood cells all work together to identify and destroy cells that have been infected by a virus.  HIV kills the cells that hunt for viruses and bacteria.  The immune system begins to fail.

Take-home message  HIV is especially difficult to control.  Mutations change the properties of the virus so that it is hard for the immune system to recognize it, and they produce variants that are resistant to the drugs being used to treat the HIV infection.