Pure culture vs. real life
• Prokaryotes exist as communities
• Biofilms
– Production controlled by density of cells
– Cells release sticky compounds
– Good & bad examples
Biofilms
Dental Plaque: aerotolerant anaerobes…
Biofilms
Staphylococcus aureusChronic infections
Diabetic foot sore
Biofilms
“The Invisible Enemy”Wired, Feb. 2007
Acinetobacter
Biofilms
Beneficial: Wastewater treatment!
Microbial Genetics
Chapter 6
Strain vs. Species:
Canisfamiliaris
Harmless E. coli Harmful E. coli
Continuity of life:
• Basic processes the same for all living things
• Metabolic pathways
– making and using energy
• How is this information passed from generation to generation?
History of Inheritance
• Positive and negative traits passed thru generations - “it’s in the blood”
• How?
• Gregor Mendel - 1860’s
– Predictable patterns
What is link between parent & offspring?
• Early 1900’s - “chromosomes” seen
• Thomas Hunt Morgan - sex linkage of traits
• How do chromosomes account for heredity?
What was the nature of the “gene”?
• DNA had been isolated from cells
• Too simple - only 4 building blocks (G,A,C,T)
• Must be proteins that are important
3 critical findings in microbiology
• Frederick Griffith
• Oswald Avery, Colin MacLeod, MacLyn McCarty
• Alfred Hershey & Martha Chase
Frederick Griffith, M.D.
• Pathogenic and nonpathogenic strains of Streptococcus pneumoniae
• Harmful strain = S
– Forms smooth colonies
– Killed mice if injected
• Harmless strain = R
– Forms “rough” (irregular) colonies
– No harm to mice
Avery, MacLeod, & McCarty
• Avery didn’t believe Griffith’s results
• Developed an in vitro system to test the switch from R-type to S-type
S-type - (smashed up & purified)
R-type cells in tubes
DNARNA
polysaccharide protein
Race to figure out DNA
• Maurice Wilkins & Rosalind Franklin– X-ray crystallographers
– King’s College, London
• Linus Pauling - Caltech– Nobel Laureate; Peace activist
– Discovered protein secondary structure
• James Watson & Francis Crick– Cambridge University
– Wire models
Lots of N & P
“Transcript”: Written copy of material that originally
appeared in another format
How is the info in the DNA accessed?
• Cells respond to chemical signals
• Some of these signals trigger genes to be “turned on” or “turned off”
• Examples?
• Result is mRNA transcript
How does protein come from DNA and RNA?
• DNA used as template for RNA
• 4 types of nucleotide bases in DNA & RNA
• Proteins made of ~20 amino acids
• What is the code?
– 1 base =
– 2 bases =
– 3 bases =
“Translate”: express in another language
Central Dogma in Biology
• Francis Crick
Continuity of life:
• Genetic code the same for all living things
• Can express
– human genes in rats
– bacterial genes in plants
– human genes in yeast
– etc…
Modern Biotechnology
• New avenues for research
• Isolate specific genes associated with diseases
• Recombinant DNA technology
– Put pieces of DNA from different organisms together
DNA Sequencing
• Computer technology pushed forward
• J. Craig Venter, Bill Clinton & Francis Collins (L to R)
Fig. 4.11
The Human Genome• ~25-30K genes
– Do NOT think of the rest as “junk DNA”
• Lots of unidentified genes
• Public vs Private funding
Changes to bacterial genomes
• Transformation
– DNA fragments from environment
• Transduction
– virus & bacterium
• Conjugation
– Bacterium & bacterium
• Mutation
• Bacteria can have separate DNA molecule
• F factor (fertility)
• Plasmid carries: – ~20 genes to allow
conjugation
– antibiotic R genes
Don’t have to be
the same species!
Spontaneous mutations are the result of natural processes
• Definition of mutation
– Change in DNA
– Can lead to change in gene = genetic diversity
• Frequency
– Changes accumulate over time (cancer)
– Each species different rate
• Mistakes during DNA processing
Induced mutations:result from a mutagen
• Mutagens
• Ultraviolet light
• Chemicals
• Benzo -a-pyrene
Mutations block DNA processes
• TT dimer distorts DNA
• No replication
• No transcription
• Fixed by repair system
– If not = mutation!
– Mutation cancer