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Lecture 10

BSCI 283 Lecture 10: Lecture 10


Department
Biological Sciences Program
Course Code
BSCI 283
Professor
Daniel Stein
Lecture
10

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Antibiotic 3/8/17
Quorum Sensing
o Means of communication between bacterial cells
o Allows bacteria to determine population density
o Provides mechanism to regulate gene expression for biofilm, etc.
o Secreted auto inducers mediate quorum sensing in bacteria
o Auto-inducer x made by cell diffuses freely through membrane
o Low concentration of auto inducerno gene expression
o High concentration of auto inducer inside bacteriagene expression
o Ex. Vibrio fischeri bacterial luciferase- enzyme that generates light
o Ex. Staphylococcus aureus- secretes peptides damage human cells
Biofilms
o Dense population of bacteria-multicellular aggregates of bacteria held together
by an extracellular polysaccharide
o Choose to live in a sessile community
o Concentrate digestive enzymes
o Persist in a favorable environment
o Aids collaborative metabolism between different species
o Eps provides for chemical and engulfment defense
o Maintains high cell density to facilitate a variety of processes
Symbiosis of Bacteria and Insects
o Ex. Leafcutter ants- bring leaves as a food source for fungus, bacteria fix nitrogen
for the cultivated fungus, the cultivated fungi are the ants essential food supply
o Ex. Fungus growing bark beetle- Streptomyces species
o Ex. Digger wasp-candidatus Streptomyces philanthi
Symbiosis of Bacteria with Mammals
o Microbes form intimate symbiotic relationships with higher organisms
o Ex. Ruminants-herbivorous animals possess special digestive organ the rumen
o Cellulose and other plant polysaccharides are digested with the help of
microbes, rumen well studied because of implanted sampling port
o All sites on a human that contain microorganisms are part of microbiome
o Microbes in gut affect early development, health and predisposition to disease
o Colonization of gut begins at birth
o High variability in gut communities between individuals
o Ex. Velicobacter pylori forms gastric ulcers and inflammation increases chance of
gastric cancer
o Coch’s postulates- steps to satisfy that microorganism causes a disease
o Antibiotic decrease velicobacter pylori but increase esophageal carcinoma
o Chemistry basis for interspecies communication
Interactions
o Secreted enzymes
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