Lecture 2 Flashcards
Spontaneous Generation
Concept that living organisms could arise spontaneously without parental organisms
Spontaneous Generation
Francesco Redi
He studied the appearance of maggots on decaying meat
1. Meat placed in unsealed jar
(Flies laid eggs on meat & maggots emerged)
2. Meat placed in a sealed jar
( Flies could not enter, no maggots)
3. Meat placed in jar covered with gauze
( Flies could not enter, no maggots)
Concluded: Maggots arise from eggs laid by flies, not spontaneous generation
In Redi’s Experiment
The meat still putrefied and microbes appeared
Spontaneous Generation
Lazzaro Spallanzani
Microbes failed to grow in sealed flask with boiled (sterile) broth
*Air required to make microbes
FINAL DISPROOF OF SPONTANEOUS GENERATION
Louis Pasteur
- Showed that microbes don’t grow in liquid till introduced from outside
- Developed “swan neck” flask, which allowed airflow, but prevented entry of dust that carried microbes
- Remained free of growth for man years
- Unless flask was tilted or broken allowing entry of microbes
BUT THERE WAS EXCEPTIONS
Ferdinand Cohn
- Observed B. Substilis growth in sterilized (boiled) media
- Discovered heat resistant form of bacteria - endospores
John Tyndall
- saw growth in media regardless of how long it was sterilized by boiling ( endospores)
- But, if he did cycles of repeated boiling and resting( four one min boils, one day apart) there was no microbial growth
DO MICROBES CAUSE DISEASE
Bassi
Fungus caused disease in silkworms
Berkeley
Fungus caused potato blight
Germ theory of disease
Many diseases are caused by microbes
Robert Koch
- Anthrax —> demonstrated the chain of infection
- Tuberculosis —> determined pure culture techniques
* won Nobel prize - Koch’s Postulates
KOCH’S POSTULATES
Criteria for establishing a causative link between an infectious agent and a disease
Criteria of Koch’s Postulate
- Microbe found in all cases of the diseases, but is absent from healthy individuals
- The microbe is isolated from the diseased host and grown in pure culture
- When microbe introduced into healthy, susceptible host ( or animal model), the host shows the same disease
- The same strain of microbe is obtained from the newly diseased host. When cultures , the strain shows the same characteristics as before
Pure culture techniques enabled a “golden age” of bacterial pathogen identification
During this time many pathogens were discovered (1876-1912)
THE FIRST VACCINES
Smallpox
In 18th century, small pox infected a large fraction of European population
Lady Mary Montagu
Introduced the practice of small pox inoculation in Europe (learned while traveling to turkey)
Edward Jenner
Deliberately infected patients with the matter from cowpox lesions ( a related but much milder disease)
- the practice of cowpox inoculation was called vaccination - Anti- vaxxers back then feared that the inoculation would turn them into cows
THE FIRST VACCINES
Louis Pasteur
- 1st to discover that attenuated strain of microbes could still confer immunity to the disease
* During his studies of fowl cholera
The way to attenuate a strain depends on the pathogen
Rabies
Required complex series of heat treatments and repeated inoculations
COROLLARY TO GERM THEORY
- Stop germ transmitting
Epidermiology
Public health measures
THE FIRST ANTIBIOTIC
Penicillin
Discovered by Alexander Fleming
- Found that Staphylococcus, he was studying were killed by substance produced by mold (Penicillium natatum)
Howard Florey &. Ernst Chain
In 1941 those biochemists were able to purify Penicillin
The first antibiotic saved lives during ww2
DISCOVERY OF VIRUSES
Tabasco mosaic disease
…
Dmitri Ivanosvsky
Surprised to find the agent of transmission could pass through a filter having pore size of 0.1um, which is known to block other microbes
Martinus Beijernick
Similar filtration experiments; concluded that it could not be a bacterial cell
Wendell Stanley
Was able to purify the particles and gets its crystal structure
-won Nobel prize chem 1946
MICROBIAL ECOLOGY
Most microbes don’t grow on typical media
Less than 0.1% of all microbial species can be cultured in the lab
Sergei Winogradsky
Amongst 1st to study microbes in their natural habitat
What did Sergei Winogradsky discover?
Beggiatoa —- oxidized hydrogen sulfide to sulfuric acid
Lithotrophs
Feeds solely on inorganic minerals
What did Sergei Develope?
Enriched cultures
* use of selective media that supports certain types of bacteria while excluding others
What did Sergei build?
A model wetland ecosystem containing regions of enrichment for microbes of diverse metabolism
* mud, organic carbon source , inorganic carbon source * After exposure to light for several weeks, several colors developed
GEOCHEMICAL CYCLING
Winogradsky and others show that bacteria perform unique roles in geochemical cycling, the global inter conversion of inorganic an organic forms of nitrogen , sulfur , phosphorus, etc.
THE MICROBIAL FAMILY TREE
Microbes are hard to classify
- hard to tell by shape
- they often reproduce asexually
- pass DNA to each other without reproduction
How to classify microbes?
Using biochemical properties like
- gram stain
- Ability to metabolize different substrates
Also use DNA Sequencing to classify
Ernst Haeckel
Recognized microbes were neither plants nor animals
Defined a 3rd kind of life - Monera
Herbert Copeland
Divided Monera into two groups
- Eukaryotic protists (Protozoa and Algae)
- Prokaryotes
Robert Whittaker
Added fungi as another kingdom of eukaryotic microbes
*Now has 5 kingdoms
Lynn Margulis
The five kingdom system modified by her
- Proposed euk. Evolved by merging with bacteria to form composite cells by intracellular endosymbiosis
- One cell internaizes another that grows within
- Mitochondria evolved from bacteria
- Cyanobacteria gave rise to chloroplasts
THE 3 DOMAINS OF LIFE
- Based on 16s ribosomal RNA (rRNA) gene sequencing
- found in all life
- Porposed by Carl Woes
Archaea
- Similar size & shape to bacteria - different biochemistry
- Ribosomes more similar to Eukaryotes
- Many live in harsh environments
- Have unique membrane lipids
