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very small is diameters 1-5 um
very numerous
-more prokaryotes in a handful of soil than total number of people who have every lived
they are able to tolerate a variety of extreme conditions
-acidic, basic, salty, hot, cold
bacteria cause half of all human diseases
-pathogens are disease causing agents
hundreds of species of beneficial bacteria in the human body
-skin, gut


bacteria and archaea

prokarotes used to be one group referred to as bacteria
studies of rRNA sequences of prokaryotes in the 1970s revelaed that many prokaryotes first classified as bacteria were actually more similar to eukaryotes
-these bacteria were then placed in a domain of their own referred to as archaea
-further comparisons revealed that some ancheael genes are more similar to eukaryotes, others are ore similar to prokaryotes, and others unique to archaea
curretn hypothesis: archaea and eukaryotes evolved from a common ancestor


differences in between bacteria and archaea

some key differences between bacteria and archaea include:
-bacteria have peptidogylan and archaea do not
this means that bacteria repsond to cell wall active antiboiotics archaea do not
-archaea have a number of different RNA polymerses bacteria have only one
archaea does not cause disease and can withstand extreme conditions
bacteria can withstand only moderate conditions


prokaryotic shapes

prokaryoktes come in a variety of shapes:
-cocci: sherical shape further characterized by arrangement
staphylococci: grape- like clusters of circles
streptococci: chains of circles
-bacilli: rod- shaped - usually as a single rod
diplobacilli: two rods together
streptobacilli: rods arranged in a chain
-spiral: helical shape
spirilla: short and rigid helical structure
spirochete: long, more flexible helical structure


bacterial structures

1. bacterial cell wall
2. capsule
3. pili
4. flagella
5. bacterial reproduction
6. endospores
7. internal structures


bacterial cell wall

-composed of sugar called peptidoglcan
-maintians cell shape, provides physcia; protection, and prevents cell from bursting in hypotonic environments
-hypertonic environments cause bacteria to shrivel-inhibiting reproduction.. explains why salt can be used in food preservation
there are two main types of bacterial cell walls:
a) gram positive: thick layer of peptidogylan
b) gram negetive: thin layer of peptioglycan with outer memebrane
these two types of stain differently during gram stain- an identification tool used in microbio lab
-pos stain purple
-neg stain pink



- a sticky layer of polysaccaride or protein covering the cell wall
found in many but not all prokaryotes
allows the bacterium to adhere:
-to other organisms
-to medical devices such as catheters
-to other surfaces
the capsule also acts to shield the mirco organisms from host defenses



-hair like appendeges
allows bacterium to adhere to one another or to thier substance
-allows adherence to rocks in streams or the lining of human intestine
-specialized pili called sex pili allow bacteria to stick to one another and transfer DNA



-this structure enables bacterial motility
-not present in all bacteria
-flaggellated bacteria may have one flagella, two flagella or many scattered all over the surface
-allows the bacteria to move towards the chemical and light stimuli called attractants away from repellent stimuli


bacterial reproduction

-replication occurs very quickly by a process called binary fission 1-2-4-8-16
-some species can reproduce in as little as 20 minutes others take 1-3 hours
-growth is limited:
-nutrients become exhausted, metabolic wastes build up
-competition from other organisms
-antibiotics are present in certain environments



-structure formed by some gram positive organisms only
-used to withstand harsh conditions
-outer cell will disintergrate and the inner cell will remain
-endospore has thick outer coat
-will dehydrate and become dormant until conditions become favourable
-can withstand heat, and cold
-when conditions are favorable it will absorb water and resume growth


internal membranes and internal structures

-prokaryotes have much simpler internal structure and genome than eukaryotes
-have specialized membranes to preform metabolic functions
-respiratory membrane: for cellualr respiration
-thylakoid membrane: for photosynthesis
-used in cyanobacteria
-prokaryotes have 1/1000 as much DNA as a eukaryote
-fewer genes highlight the simplicity of the cells required activities
-cells may have plasmids: smaller pieces of DNA acquired from other bacteria which contain specialized genes
ex) antibiotic resistance genes
-prokaryotes have smaller ribosomes (70s) than eukarotes (80s)
-this difference in ribosomal size and structure make them an important antibiotic target


metabolic diversity of prokaryotes
two types of metabolic resources:

prokaryotes require two main metabolic resources :
1. a source of energy
2. a source of carbon


source of energy

prokaryotes can either use light or chemicals
1. light: phototroph
2. chemicals: chemotroph


source of carbon

some prokaryotes make their own carbon compounds while others require pre-formed carbon
1. autotrophs: use an inorganic carbon dioxide is used to form organic carbon such as glucose
-this process is called photosynthesis
2. heterotrophs: obtain their carbon from organic compounds such as glucose


mode of nutrition

based on the source of energy a prokaryote uses and the form of carbon that it uses to ontian organic carbon, prokaryotes can be assigned a mode of nutrition, there are four classifications
1. photoautotrophs
2. chemoautotrophs
3. photoheterotrophs
4. chemoheterotrophs



-bacteria lives as individual cells (stand alone)
-they may also live in surface coating colonies called biofilms
-they form when bacterial cells secrete signaling molecules which recruit nearby cells
-when the colony reaches a sufficient size the bacterial cells of the colony begin producing protiens that cause them to stick to a particular surfcae and to each other
-there are channels within the biofilm which all nutrients and wastes to leave
-in humans:
-biofilms allow bacteria to adhere to teeth causing cavity (dental carries)
-they also form on catheters and other medical devices causing serious problems
--they are benefical when used in water sewage treatment facilities


archaea live in extereme environements

-archeaea are able to live in environments where few other organisms are able to survive
-they have unsusual protiens and other molecular adaptations that allow them to survive and reproduce where few other organisms can
-there are three main groups of archaea formed on the basis of the environemtn in which they are found:
1. extereme halophiles
2. extereme thermophiles
3. methanogens


extreme halophiles

these archaea that thrive in waters with high salt concentrations
-15-30% salt concentration
(sea water = 3% salt concentration)


extereme thermophiles

archaea that thrive in water of very high temps
some live near deep ocean vents where temps exceed 100 degrees



archaea that live in anaerobic environments
produce methane as a waste product
can be found in anaerboic mud at the bottom of lakes and swamps
these also live in the intestinal tract of humans
responsible for human gas which results from methanogen metabolism
even though archaea are dubbed exteremeophiles they are also abundant in moderate environments as well (versitle)


bacteria are diverse

the domain bacteria is divided into 9 groups:
(only 5)
- proteobacteria
-the gram positive



composed of gram negative organisms
5 subgroups:
alpha: including rhizobium species which live in plant roots and fix nitrogen from the atmosphere fro the plant
-gramma: including salmonella, ecoli, and photosynthetic sulfur bacteria that oxidize H2S
-delta: includes slime secreting myxobacteria which form elabroate colonies and bdellovirbiro which attack other bacteria



these bacteria live inside ekaryotic cells
chlamydia trachomatis causes blindess in developing areas and is responsible for most prevalent sexually transmitted infection



these bacteria are helical in shape
these are well known pathogens
treponema pallidmum causes syphilis
borrelia burgdorferi causes lyme diease


the gram positive

rivals the proteobacteria in terms of diversity
incluses staphylocacous spp. and strepococcus spp.
stretpmyces within this group are used by pharmaceutical companies to produce antibodies shich as streptomycin



these are prokaryotes that function to generate oxygen via plant like photosynthesis
the stromatolite fossils discussed in this course were generated by ancient cyanobacteria
cyanobacteria are thought to be responsible for generating the oxygen that made the atmosphere aerobic
modern day cyanobacteria provide a large amount of food for fresh water and marine ecosystems


diease causing bacteria

bacteria capable of causing diease are usually fought off by the host immune system
sometimes these defenses fail and the pathogens establishes itself in the body causing illness
bacteria that cause illness usually do so by producing toxins which are essentially poisions
there are two classes of bacterial toxins
1. exotoxins
2. endotoxins



can only get this from gram neg
these are secreted by the bacterial cell into the surroundin environment
ex) tetanus toxin and botulinum toxin
staphlococcus is also an exotoxin producer
toxic shock syndrome



these are compounds of the outer membrane of gram negative bacteria
these toxins are only harmful when they are relased which occurs when the bacterial cell dies
endotoxins always csuse the same symptoms:
sometimes a dangerous drop in blood pressure: septic shock
ex) samonella which causes food poisoning


improvements to disease causing bacteria

bacterial disease has been drastically decreased during the last century due to a number of important changes
-improved sanitation and hygiene
-water treatment and sewage systems
-vaccine and antibiotic development, discovery and use


bacteria and bioterrorism

bacillus anthracus spores used in mail attacks of the united states
-this bacteium forms hardy endospores
spores are commonly found in soil
contact with the spores via skin cuts is easy to treat
inhalation of spores is deadly
-an inhalation form of spores are produced and are inhaled by the target population: bioterrorism
-once inhaled the spores begin to germinate int he lungs because conditions are optimal for growth
-mutliplying bacteria produce an exotoxin that accumulates in the blood
-the bacterium can be treated with antibiotic but the antibiotic is useless against the toxin that is already in the blood
yersina perstis the bacterium that causes the plague - easily spread by aerosols
the botulinum toxin produced by clostidium botulinum
-bacteium produces resistant spores
-botox is one of the most potent toxins known


prokaryotes help clean up the environment

prokaryotes are vital to our well being
because prokaryotes are metabolically diverse we use them to assist in environmental problems:
-bioremediation: this is the use of organisms to remove pollutants from the soil, water or air
bacteria are key in sewage treatments:
solid sewage is treated with anerobic bacteria which breaks down the organic matter so that it may be sued as fertilizer
the liquid waste is passed along biofilms of bacteria and archaea adhered to rock
-the organisms of the biofilm digest much of the organic matter in the liquid
-bacteria are also important in the cleaning of oil spills and old mining sites