《遗传学》课程教学资源：英文版 Bacterial Genetics

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

Three kinds of genetic transfer occur in bacteria Transformation: donor cell releases dNa by lysi S and it is taken up by the recipient cell Conjugation: physical contact between two bacterial cells and transfer of dna Transduction: bacterial virus(phage) transfers the DNa from donor cell to recipient cell

Three kinds of genetic transfer occur in bacteria • Transformation: donor cell releases DNA by lysis and it is taken up by the recipient cell • Conjugation: physical contact between two bacterial cells and transfer of DNA • Transduction: bacterial virus (phage) transfers the DNA from donor cell to recipient cell

Gene Transfer in Bacteria Gene transfer in bacteria Transformation Conjugation Transducti。n ce∥?2 Recipi Lysis of Don。rcel Donor ce∥ Recipient cell don。rcel releases DNA into medium. Donor cell Donor dNa is packaged plasmid in bacteriophage OO C Recipient Donor dna is Lysis of don。 or cell. cell transferred directly to Donor dNa is packaged recipient through in released bacteriophage connecting tube Contact and transfer are promoted by a specialized plasmid Donor dna is in the donor cell Donor dNa is transferred taken up by recipient. when phage particle infects recipient cell

Gene Transfer in Bacteria

Bacterial transformation Transformation involves uptake of DNA, followed by either recombination of the dna with the host chromosome or self-replication of DNA (plasmids). Genes that are close together on DNA can cotransform That is, alleles of both genes can be inserted on the same piece of DNA. Gene order can be determined by cotransformation

Bacterial transformation • Transformation involves uptake of DNA, followed by either recombination of the DNA with the host chromosome or self-replication of DNA (plasmids). • Genes that are close together on DNA can cotransform. That is, alleles of both genes can be inserted on the same piece of DNA. • Gene order can be determined by cotransformation

Natural transformation 力isB hisB trpc trpc Wildtype donor cell trpc/hisB double auxotrophs Recipient cell (b) Competent cell recipient Donor dna Bacterial chromosome (hisB", trpC) Receptor site 1. Donor DNa binds to recipient cell at receptor site 力isB trpc+

Natural Transformation

2. One donor strand is degraded. Admitted donor strand pairs witi homologous region of bacterial chromosome. Replaced strand is degraded One strand degraded 3. Donor strand is integrated into bacterial chromosome hisB trpC 4. After cell replication, one cell is identical to original recipient the other carries the mutant gene. hisB trpc Transformed cell Figure 13.10 Natural transformation in B. subtilis