Chapter 9 Outline
Gene Transfer, Genetic Engineering, and Genomics
Introduction
9.1 Genetic Recombination in Prokaryotes
• Genetic Information in Prokaryotes Can Be Transferred Vertically and
Horizontally
• Vertical gene transfer (VGT) is the transfer of genetic material from
parent cell to daughter cell
• Horizontal gene transfer (HGT) is the transfer of DNA from a donor cell
to a recipient cell
• Transformation Is the Uptake and Expression of DNA in a Recipient Cell
• By integration of a new DNA fragment, the recipient has gained some
ability it previously lacked
• Transformation was first described by Frederick Griffith in 1928
• Competence is the ability of a recipient cell to take up DNA from the
environment
• Conjugation Involved Cell-to-Cell Contact for Horizontal Gene Transfer
• In conjugation, a donor cell transfers DNA directly to the recipient
• The donor cell forms a conjugation pilus to make contact with the
recipient
• The F factor DNA in the donor replicates by the rolling-circle mechanism
• Conjugation also Can Transfer Chromosomal DNA
• High frequency of replication (Hfr) strains can donate chromosomal genes
rather than just the F plasmid
• The F factor attaches to the chromosome using an insertion sequence
• Conjugation is usually interrupted before the entire chromosome is
transferred,
• The recipient remains F- (called a recombinant F-)
• If an integrated F plasmid breaks from the chromosome, taking a fragment
of chromosomal DNA, it is called an F' plasmid
• Transduction Involves Viruses as Agents for Horizontal Transfer of DNA
• In transduction, a virus (bacteriophage) carries a chromosomal DNA
fragment from donor to recipient
• In the lytic cycle, virulent phages
• destroy the host chromosome
• replicate themselves
• destroy the cell
• In the lysogenic cycle, temperate phages integrate their DNA into the host
chromosome (as a prophage)
• Virulent phages perform generalized transduction
• A fragment of host cell DNA ends up in the phage during
packaging, which they transfer to a new host cell
•
In the lysogenic cycle, the prophage eventually excises itself from the host
chromosome
•
Sometimes it takes a few flanking host genes and leaves a few
phage genes behind
9.2 Genetic Engineering and Biotechnology
• Genetic Engineering Was Born from Genetic Recombination
• Genetic engineering involves changing the genetic material in an organism
to alter its traits or products
• A recombinant DNA molecule contains DNA fragments spliced together
from 2 or more organisms
• Specific fragments can be obtained by cutting short stretches of
nucleotides with a restriction endonuclease
• The fragments are joined by DNA ligase
• Genetic Engineering Has Many Commercial and Practical Applications
• The genes responsible for producing human insulin can be cloned into
bacteria
• Bacteria could be genetically engineered to
• break down toxic wastes
• produce antibiotics
• Plants have been engineered using microbial genes for
• herbicidal activity
• viral resistance
• Cows produce more milk when injected with bovine growth hormone produced
by engineered bacteria
• Specific nucleotide sequences in pathogens allow us to identify them using DNA
probes
• Recombinant vaccines can be safer than traditional vaccines using killed
or attenuated microbes
• DNA vaccines are being developed in which a gene serves as the vaccine
8.3 Microbial Genomics
• Many Microbial Genomes Have Been Sequenced
• Hundreds of microbial genomes have been sequenced since the first in
1995
• Many of which are pathogens
• Segments of the Human Genome May Have “Microbial Ancestors”
• As many as 200 of the 35,000 human genes are essentially identical to
those of Bacteria
• They were passed down from early ancestors of humans
• Microbial Genomics Will Advance Our Understanding of the Microbial World
• Knowing genomes of bacteria that cause food-borne diseases can help us
• develop detection methods
• make food safer
• It can help us identify microbes that cannot be cultured in the lab
• Environmental genomics helps us understand how microbial communities
function
• Improved biosensing
• Comparative Genomics Brings a New Perspective to Defining Infectious Diseases
and Studying Evolution
•
•
Functional genomics attempts to discover
• the function of proteins coded for in a genome
• how the genes interact, allowing the microbe to grow and
reproduce
• Comparative genomics compares the DNA sequence of one microbe to
another similar or dissimilar organism
Metagenomics is identifying the previously unseen microbial world
• Techniques are now being developed to analyze and understand all the
genomes within a microbial community