Chapter 1 - Humans and the Microbial World
experiments of Louis Pasteur
- French chemist considered "father of modern microbiology" - demonstrated air is filled with microorganisms * filtered air through cotton plug * observed trapped microorganisms * many looked identical to those found in broths - developed swan necked flask * boiled infusions remained sterile despite opening to air * ended arguments that unheated air or broths contained "vital force"
Ferdinand Cohn (1876)
- German botanist that discovered endospores
experiments of John Tyndall
- Pasteur's results were not fully reproducible so English physicist, John Tyndall, finally explained conflicting data - proved Pasteur correct - sterilizing broths required different times * some sterilized in 5 minutes; others not, despite 5 hours - realized hay infusions contained heat resistant microbes * this contaminated labs using hay
beneficial microbes...
- all surfaces of human body populated by microorganisms - normal microbiota - prevent diseases by competing with pathogens - development of immune system response - aid in digestion
Robert Hooke
- also credited with discovery of microbiology - described 'microscopical mushroom' (common bread mold) in 1665
the living world of microbes has enormous numbers
- bacterial species outnumber mammalian species by a factor of 10,000 - considerations of biodiversity typically overlook enormous contribution of microbes - less than 1% of all microbial species can be grown and studied in laboratory
commercial benefits of microbiology - food production
- baking bread using yeast * Egyptian bakers as early as 2100 BC - fermentation of grains to produce beer * Egyptian tombs revealed as early as 1500 BC - fermentation of milk * yogurt, cheese, buttermilk
commercial benefits of microbiology - bacteria synthesizes commercially valuable products
- cellulose ( stereo headsets) - hydroxybutric acid (manufacture of disposable diapers and plastics) - ethanol (biofuel - hydrogen gas (possible biofuel) - oil (possible biofuel) - insect toxins (insecticides) - antibiotics (treatment of disease) - amino acids (dietary supplements)
commercial benefits of microbiology - biodegradation
- degrades PCBs, DDT, trichloroethylene, and others - help clean up oil spills - bioremediation
Antony van Leeuwenhoek (1632 - 1723)
- drapery merchant - made simple magnifying glass - studied lake water - observed 'animalcules'
size in the microbial world
- enormous range * largest eukaryotic cells ~a million times larger than smallest virus - wide variations even within a group * bacterium ~600 um x 80 um discovered in mid 1990s (visible to naked eye) * bacterium 70 times larger in volume discovered in 1999 *eukaryotic cell ~1 um found (similar in size to typical bacteria)
domain Eukarya
- eukaryotic - unicellular or multicellular - no peptidoglycan - microbial members include fungi, algae, and protozoa * algae and protozoa also termed protists * some multicellular parasites including helminths (roundworms, tapeworms) considered as well
acellular infectious agents - prions
- infectious proteins - misfolded version forces normal version to misfold * abnormal proteins bind to form fibrils * cells unable to function - cause several neurodegenerative diseases in humans and animals * most widely recognized example is bovine spongiform encephalopathy (BSE) = "mad cow disease" - resistant to standard sterilization procedures
commercial benefits of microbiology - genetic engineering
- introduction of genes into another organism - disease resistant plants - production of medications (insulin for diabetes)
Second Golden Age of Microbiology
- less than 1% of prokaryotes ever studied - most do not grow in lab - new sequencing approaches revealing enormous biodiversity of microbial world * 1,800 new bacterial species found in Sargasso Sea - major challenges remain - exploring microbial world should answer many fundamental biological questions
domain Archaea
- like Bacteria, Archaea are prokaryotic - unicellular - similar shapes, sizes, and appearances to Bacteria - rigid cell walls - multiply via binary fission - may move via flagella - major differences in chemical composition * cell wall lacks peptidoglycan * ribosomal RNA sequences different - many are extremophiles * they can live under high salt concentration or high temperature
microbes and disease
- most microorganisms are not harmful - some are pathogens (they can cause disease) * influenza 1918 - 1919 killed more Americans than died in WWI, WWII, Korean, Vietnam, and Iraq wars combined - modern sanitation, vaccination, and effective antimicrobial treatments have reduced incidences of the worst diseases
Golden Age of Microbiology
- most pathogenic bacteria identified (1875 - 1918) - work on viruses began - understanding that microscopic agents could cause disease led to control efforts - huge improvements in past century inhuman health * antibiotics to treat infectious diseases * vaccines to prevent diseases
acellular infectious agents - viruses
- nucleic acid packaged in protein coat - variety of shapes - infect living cells, termed hosts - multiply using host machinery and nutrients - inactive outside of host thus, viruses are obligate intracellular parasites - all forms of life can be infected by different types
microorganisms
- organisms too small to see with the naked eye - examples: bacteria, protozoa, and some fungi and algae - foundation for all life on earth - existed for ~3.5 billion years - plants, animals, and modern microorganisms all evolved from ancestral bacteria - our life depends on their activities
prokaryotic cells
- 'prior to nucleus' - typically these cells do not have a membrane bound nucleus or any other membrane bound organelles - the genetic material is located in a region called the nuclei - Bacteria and Archaea
eukaryotic cells
- 'true to nucleus' - the genetic material in these cells is contained within a membrane bound nucleus - these cells often have a variety of other organelles - more complex than prokaryotic cells - Eukarya
detractors of spontaneous generation theory
- Francesco Redi - Louis Pasteur - John Tyndall (each contributed to disproving the theory)
emerging diseases
- pathogens can become resistant to antimicrobial medications (tuberculosis, malaria) - increased travel and immigration * many diseases eliminated from developed countries still exist in many parts of the world (malaria, cholera, plague, yellow fever) - changes in population * weakened immune systems (elderly, HIV/AIDS people)
living organisms are all composed of cells with one of two basic structures...
- prokaryotic - eukaryotic
acellular infectious agents - viroids
- simpler than viruses - require host cell for replication - consist of single short piece of RNA - no protective protein coat - cause plant diseases - some scientist speculate they may cause diseases in humans * no evidence yet
domain Eukarya - protozoa
- single celled - complex, larger than prokaryotes - most ingest organic compounds - no rigid cell wall - most motile
domain Eukarya - fungi
- single celled (yeasts) or multicellular (molds, mushrooms) - gain energy from degradation of organic materials * recyclers * food/beverage * pathogens - primarily live on land
domain Eukarya - algae
- single celled or multicellular - photosynthetic * contain chloroplasts with chlorophyll or other pigments - primarily live in water - rigid cell walls - many have flagella
domain Bacteria
- single celled prokaryotes - unicellular - most have specific shapes (rod, spherical, spiral) - rigid cell wall contains peptidoglycan (unique to bacteria) - multiply via binary fission - many move using flagella
binomial system of nomenclature
- two words - genus = first name (first letter always capitalized) - species = second name indicates the specific epithet (not capitalized) - genus and species (whole name) always italicized or underlined
re-emerging diseases
- vaccination can become victim of own success - lack of firsthand knowledge of dangers of diseases can lead people to fear vaccines more than the diseases * diseases such as measles, mumps, and whooping cough nearly eradicated from U.S. but could re-emerge with declining vaccination rates
domain...
all living organisms can be classified into one of three groups: - Bacteria - Archaea - Eukarya
plague...
another major killer in history - ~1/3 of population of Europe (or ~25 million individuals) died between 1346 - 1350 - today, fewer than 100 die worldwide - control of rodent population harboring bacterium - antibiotics available
science of microbiology...
born in 1674
obligate intracellular parasites
can not replicate outside of a host
vegetative cell
cell of bacterium or unicellular alga that is actively growing rather than forming spores
Father Lazzaro Spallanzani (1776)
contradicted Needham's results - boiled broths longer and sealed flasks by melting necks - broths remained sterile unless neck cracked
Robert Koch
demonstrated that anthrax is caused by a spore-forming bacterium
John Needham (1749)
demonstrated that boiled broths still produced microorganisms
germination
development of a plant from a seed or spore after a period of dormancy (endospore goes through this process)
explanation of differences between Pasteur's results and those of other investigators
extreme heat resistance of endospores - Pasteur used broths made with sugar or yeast extract - highlights importance of reproducing all conditions as closely as possible when conducting research
sporulation
formation of endospore (vegetative cell goes through this process)
endospores
heat resistant form of bacteria - only for survival (not reproductive) - examples: Bacillus (Anthrax) and Clostridium (Tetrus, Botulism)
non-living members of the microbial world...
include viruses, viroids, and prions - acellular infectious agents - not microorganisms, so general term microbe often used
emerging infectious disease
infectious disease that has become more common in the last 35 years - examples: E. coli (normal flora), E. coli 0157.H7 (hemolytic uremic syndrome), mad cow disease (prions/infectious proteins), swine flu, severe acute respiratory syndrome (SARS), multi drug resistant tuberculosis, lyme disease, hepatitis C, acquired immunodeficiency syndrome, hemolytic uremic syndrome, hantavirus pulmonary syndrome, west nile encephalitis - changing lifestyles increase opportunities to spread * closer contact with animals = hantavirus - evolution of infectious agents previously unable to infect humans (HIV/AIDS, SARS)
to disprove spontaneous generation of microorganisms...
it took another 200 years due to conflicting results between laboratories
spontaneous generation
life arises spontaneously from non-living material
chronic diseases...
may be caused by bacteria - peptic ulcers are caused by Helicobacter pylori, NOT stress - possibly indigestion, Crohn's disease, and others
infectious proteins
misfolded versions of normal cellular proteins found in brain
remaining disease challenges...
much work remains - especially true for viral diseases and diseases associated with poverty - respiratory infections and diarrheal diseases cause most illness and deaths in world today * in United States, ~750 million infections * ~200,000 deaths * cost in tens of billions of dollars
normal microbiota
normal flora
acellular infectious agents
not composed of cells, not alive
we could not survive without microorganisms...
numerous benefits - examples: nitrogen fixation, oxygen production, degradation of waste materials (cellulose, also sewage and wastewater) but, - have killed more people than have ever been killed in war - used as weapons, and bioterrism attacks
bacteria needs ___ to reproduce
nutrients, water, and temperature
binary fission
process in which one cell enlarges and then divides, which forms two cells each equivalent to the original
biogenesis
production of living things from other living things - Louis Pasteur's experiments led to this theory
controversy still unsolved...
some argued heating destroyed "vital force" necessary for spontaneous generation
microbiology
study of the microbial world (made up of members too small to be seen without the aid of a microscope)
microbe
term used when referring to general members of the microbial world
microorganisms are wonderful model organisms to study because...
they have the same fundamental metabolic and genetic properties as higher life forms - all cells composed of the same chemical elements - synthesize structures in similar ways - replicate DNA - degrade foods via metabolic pathways - "What is true of elephants is also true of bacteria, and bacteria are much easier to study" (Nobel Prize wining microbiologist Dr. Jacques Monod)
commercial benefits of microbiology - biotechnology
use of microbiological and biochemical techniques to solve practical problems
Francesco Redi (1668)
used simple experiment to show that worms found on rotting meat originated from the eggs of flies, not from the decaying meat (as supporters of spontaneous generation believed) - placed meat in two jars - covered one jar with gauze - gauze prevented flies from depositing eggs - no eggs = no worms
bioremediation
using microorganisms to hasten decay of pollutants
smallpox...
viral disease that was once a leading killer - ~10 million deaths over 4,000 years - devastating on unexposed populations (Aztecs in New World) - worldwide eradication attempts eliminated disease * no reported cases since 1977
microbial world also includes...
viruses and other infectious agents that are not considered organisms because they are not composed of cells; they are acellular