Chapter 1

Question 1

What is a Microbe?

Answer 1

• a living organism that requires a microscope to be seen
• range in size from about a millimeter (mm) to 0.2 micrometer (µm) – average is 1-2 µm
• Most microbes consist of a single cell, but some are multicellular
• represented in each of the three domains of life

Question 2

Genome

Answer 2

-the total genetic information contained in an organism’s chromosomal DNA

Question 3

Metagenome

Answer 3

• collection of DNA sequences obtained from a mixture of organisms in an environmental sample
• useful for studying microbiomes

Question 4

Microbiome

Answer 4

-all of the different microbes in a particular environment

Question 5

How may DNA base pairs in a bacterial chromosome?

Answer 5

~2 million

Question 6

How many genes in a bacterial chromosome?

Answer 6

• 1 gene is about 1000 bases

- most have 2,000-4,000 genes

Question 7

Microbes Shape Human History

Answer 7

• They affect the environment
• Some produce oxygen, fix nitrogen, decompose organic material
• “Rock-eating” bacteria, lithotrophs, enabled mining of metals
• Yeasts and bacteria modify foods and beverages

Question 8

Microbial Disease

Answer 8

• profoundly affected human demographics and cultural practices.
• Fourteenth century (January 1, 1301, to December 31, 1400): bubonic plague caused by Yersinia pestis
• Nineteenth century: tuberculosis caused by Mycobacterium tuberculosis
• Today: acquired immunodeficiency syndrome (AIDS) caused by the human immunodeficiency virus (HIV)
• more soldiers have died of microbial infections than of wounds in battle

Question 9

Antonie van Leeuwenhoek (1632–1723)

Answer 9

• Built single-lens magnifiers, complete with sample holder and focus adjustment
• First to observe single-celled microbes

Question 10

Spontaneous generation

Answer 10

the theory that living creatures could arise without parents

Question 11

Louis Pasteur (1860s)

Answer 11

• discovered the microbial basis of fermentation
• Devised “swan-neck” flasks
• Showed that, after boiling, the contents remain free of microbial growth, despite access to air

Question 12

Germ theory of disease

Answer 12

many diseases are caused by microbes

Question 13

Robert Koch (1843–1910)

Answer 13

-Founder of the scientific method of microbiology
-Applied his methods to numerous lethal diseases around the world
Working with anthrax demonstrated an important principle of epidemiology: the chain of infection, or transmission of a disease

Question 14

Koch’s Postulates

Answer 14

Criteria for establishing a causative link between an infectious agent and a disease

1. Microbe is always present in diseased host and is absent in healthy individuals
2. Microbe can be grown in pure culture and characterized (no other microbes present)
3. Introduction of the pure microbe into healthy hosts causes the original disease
4. Same microbe (characterized in step 2) is re-isolated from now-sick individual (from step 3)

Question 15

antiseptic

Answer 15

• doctors order to wash their hands with chlorine
• kills microbes
• too hash to use internally
• led to aseptic surgery

Question 16

Alexander Fleming (1929)

Answer 16

• discovered that Penicillium mold generated a substance that kills bacteria
• In 1941, purified penicillin became available
• The first commercial antibiotic to save human lives

Question 17

Viruses

Answer 17

are acellular obligate intracellular parasites of cells that cannot grow or replicate on their own

Question 18

Microbial Ecology

Answer 18

• Microbes are found in nearly all environments
• Microbes cycle minerals essential for all life, including carbon, nitrogen, and oxygen
• less than 0.1% of all microbial species have been cultured in the laboratory

Question 19

Sergei Winogradsky (1856–1953)

Answer 19

• A Russian scientist who was among the first to study microbes in natural habitats
• Discovered lithotrophs (rock eaters)
• Developed enrichment cultures to find bacteria present in particular environments
• Invented the Winogradsky column= A wetland model ecosystem containing regions of enrichment for microbes of diverse metabolism

Question 20

geochemical cycling

Answer 20

pathway that chemical elements take in the surface and crust of the Earth

Question 21

Endosymbionts

Answer 21

• microbes livings symbiotically inside a larger organism
• Endosymbiotic bacteria known as rhizobia induce the roots of legumes to form special nodules to facilitate bacterial nitrogen fixation

-Endosymbiotic microbes make essential nutritional contributions to host animals

Question 22

Biofilms

Answer 22

complex structure adhering to surfaces that are regularly in contact with water, consisting of colonies of bacteria and usually other microorganisms that secrete a mucilaginous protective coating in which they are encased

Question 23

2 Challenges to Classify Microbes

Answer 23

1. Resolution of the light microscope was too low
   - Many microbes look the same
   - Challenge was overcome via advances in biochemistry and microscopy
   - Now, DNA sequence is used to identify and classify microbes
2. Microbial species are hard to define (because they are asexual)
   - A working definition of microbial species: 95% similarity of DNA sequence

Question 24

Lynn Margulis

Answer 24

• modified the five-kingdom system dramatically
• proposed that eukaryotic organelles, such as mitochondria and chloroplasts, evolved by endosymbiosis from prokaryotic cells engulfed by pre-eukaryotes

Question 25

Carl Woese 1977

Answer 25

• studying recently discovered prokaryotes that live in hot springs and/or produce methane
• Analysis of the 16S rRNA nucleotide sequence revealed that these prokaryotes were a distinct form of life
• He called them archaea

Question 26

3 domains of life

Answer 26

1. Bacteria
2. Archaea
3. Eukarya

-bacterial ancestor of mitochondria derives from ancient proteobacteria, whereas chloroplasts derive from ancient cyanobacteria