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
Transformation of bacterial cells Transformation does not naturally occur in most strains of bacteria, including E. coli E coli and other bacteria can be forced to take up DNA by special chemical and temperature treatments DNA can also be put into bacterial cells by first treating the cells with a brief high voltage pulse (electroporation) This causes a temporary production of pores in the cell membrane, allowing the dNa to pass into the cell
Transformation of bacterial cells • Transformation does not naturally occur in most strains of bacteria, including E. coli. • E. coli and other bacteria can be forced to take up DNA by special chemical and temperature treatments • DNA can also be put into bacterial cells by first treating the cells with a brief high voltage pulse (electroporation). This causes a temporary production of pores in the cell membrane, allowing the DNA to pass into the cell
Bacterial conjugation (a) strain A Mixture of Strain B met bio thrt A and b met+ bio+ thr (b) Cotton plug Medium moved through filter leu+ thi+ leu thi usIng pressure or suctio Strain A Strain B For each sample, wash and plate -10 cells onto Filter minimal medium After incubation cells plated onto minimal medium. No growth met++ bio+ thr* No growth leu+ thi+ cells grow into colonies No growth No growth
The sex factor F DNA transfer is mediated by f, the fertility factor F is a plasmid, a small self-replicating circle of DNA F carries genes that direct the formation of the conjugation tube and its replication and transfer to the recipient The F-factor replicates and a new copy is sent into the F- recipient cell. The F-factor is an example of a conjugative plasmid
The sex factor: F • DNA transfer is mediated by F, the fertility factor. • F is a plasmid, a small self-replicating circle of DNA. • F carries genes that direct the formation of the conjugation tube and its replication and transfer to the recipient • The F-factor replicates and a new copy is sent into the Frecipient cell . The F-factor is an example of a conjugative plasmid