Chapter 1 Flashcards
(26 cards)
What is a Microbe?
- 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
Genome
-the total genetic information contained in an organism’s chromosomal DNA
Metagenome
- collection of DNA sequences obtained from a mixture of organisms in an environmental sample
- useful for studying microbiomes
Microbiome
-all of the different microbes in a particular environment
How may DNA base pairs in a bacterial chromosome?
~2 million
How many genes in a bacterial chromosome?
- 1 gene is about 1000 bases
- most have 2,000-4,000 genes
Microbes Shape Human History
- 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
Microbial Disease
- 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
Antonie van Leeuwenhoek (1632–1723)
- Built single-lens magnifiers, complete with sample holder and focus adjustment
- First to observe single-celled microbes
Spontaneous generation
the theory that living creatures could arise without parents
Louis Pasteur (1860s)
- 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
Germ theory of disease
many diseases are caused by microbes
Robert Koch (1843–1910)
-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
Koch’s Postulates
Criteria for establishing a causative link between an infectious agent and a disease
- Microbe is always present in diseased host and is absent in healthy individuals
- Microbe can be grown in pure culture and characterized (no other microbes present)
- Introduction of the pure microbe into healthy hosts causes the original disease
- Same microbe (characterized in step 2) is re-isolated from now-sick individual (from step 3)
antiseptic
- doctors order to wash their hands with chlorine
- kills microbes
- too hash to use internally
- led to aseptic surgery
Alexander Fleming (1929)
- discovered that Penicillium mold generated a substance that kills bacteria
- In 1941, purified penicillin became available
- The first commercial antibiotic to save human lives
Viruses
are acellular obligate intracellular parasites of cells that cannot grow or replicate on their own
Microbial Ecology
- 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
Sergei Winogradsky (1856–1953)
- 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
geochemical cycling
pathway that chemical elements take in the surface and crust of the Earth
Endosymbionts
- 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
Biofilms
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
2 Challenges to Classify Microbes
- 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 - Microbial species are hard to define (because they are asexual)
- A working definition of microbial species: 95% similarity of DNA sequence
Lynn Margulis
- 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
