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