Bacterial Genetics Key Requirements 1. Understand how genetic mapping is achieved in bacteria: Co-transformation F factor hfr strain co-transduction and some understanding of phage genetics 2. Read the textbook and do the problem set at the back
Bacterial Genetics Key Requirements: 1. Understand how genetic mapping is achieved in bacteria: Co-transformation, F factor, Hfr strain, co-transduction and some understanding of phage genetics 2. Read the textbook and do the problem set at the back
General Introduction about e coli E coli is widely used in genetic studies. E coli grows quickly, grows on a simple media and there are many auxotrophic mutant strains Many different bacterial mutants types have been identified Mutants unable to utilize a nutrient for growth: gal-, lac-, xyl-,etc Mutants dependent upon a nutrient for growth- an auxotroph: ala-, phe-, leu-, etc Mutants sensitive or resistant to a drug or phage: tetR Conditional mutations: grow only under certain conditions dnaAts
General Introduction about E.coli • E. coli is widely used in genetic studies. • E. coli grows quickly, grows on a simple media and there are many auxotrophic mutant strains. • Many different bacterial mutants types have been identified: • Mutants unable to utilize a nutrient for growth: gal-, lac-, xyl-, etc • Mutants dependent upon a nutrient for growth--- an auxotroph: ala-, phe-, leu- , etc • Mutants sensitive or resistant to a drug or phage: tetR • Conditional mutations: grow only under certain conditions dnaAts
An experiment to isolate auxotroph Penicillin enrichment Resuspend in medium minus Auxotr。phs one nutrient Transfer to Centrifuge plus penicillin rich medium Replica plate。n Cell pellet medium minus nutrient Mutagenized Prototrophs gr。w culture in rich and 99% are killed by medium c。 ntains penicillin Auxotrophs auxotrophic and cannot grow and are prototrophic cells not killed. Culture is Only prototrophs grow enriched for Locate auxotrophic auX。 trophs. colonies on original late
An experiment to isolate auxotroph
The bacterial chromosome and plasmids Most or all bacteria possess only one chromosome, and it is circular The size of bacterial chromosomes vary from 1.5 mega-base pairs to 8 mega-base pairs. E coli is 4.8 mega-base pairs(4, 800,000). Several have had their DNA sequence determined. Nearly all bacteria possess plasmids Plasmids are small (usually between 2,000 to 100,000 bp) extrachromosomal circular dNAs that replicates autonomously from the chromosome) Many plasmids possess specialized genes: antibiotic resistance, ability to degrade specialized chemicals, or genes for specific purposes: nitrogen fixation, toxin production, etc. Some possess genes for transfer to other bacteria
The bacterial chromosome and plasmids • Most or all bacteria possess only one chromosome, and it is circular • The size of bacterial chromosomes vary from 1.5 mega-base pairs to 8 mega-base pairs. E. coli is 4.8 mega-base pairs (4,800,000). Several have had their DNA sequence determined. • Nearly all bacteria possess plasmids. • Plasmids are small (usually between 2,000 to 100,000 bp) extrachromosomal circular DNAs that replicates autonomously from the chromosome) • Many plasmids possess specialized genes: antibiotic resistance, ability to degrade specialized chemicals, or genes for specific purposes: nitrogen fixation, toxin production, etc. • Some possess genes for transfer to other bacteria
Bacterial Plasmid (b) Tn5 n3 1S1 Kan / IS1 Tn4 Resistance-determinant -- segment IS2
Bacterial Plasmid