Gene Transfer, Genetic Engineering, and Genomics Chapter 9 Gene Transfer, Genetic Engineering, and Genomics

9.1 Bacterial Cells Can Recombine Genes in Several Ways 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. Figure 09.02: Gene transfer mechanisms.

Transformation was first described by Frederick Griffith in 1928. 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. Investigating the Microbial World 9: Transformation Experiments of Griffith.

Figure 09.03: Transformation In a Gram-Positive Cell. Competence is the ability of a recipient cell to take up DNA from the environment. It may give the recipient the ability to be more pathogenic. Figure 09.03: Transformation In a Gram-Positive Cell.

Figure 09.04: Bacterial conjugation in E. coli. Conjugation involves cell-to-cell contact for horizontal gene transfer. In conjugation, a donor cell (F+) transfers DNA directly to the recipient (F-). The donor cell forms a conjugation pilus to make contact with the recipient. Figure 09.04: Bacterial conjugation in E. coli. © Dr. Dennis Kunkel/Visuals Unlimited

The F factor DNA in the donor replicates by the rolling-circle mechanism. Figure 09.05A: Conjugation.

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- If an integrated F plasmid breaks from the chromosome, taking a fragment of chromosomal DNA, it is called an F' plasmid. Figure 09.05B: Conjugation.

Transduction uses viruses for horizontal transfer of DNA. In transduction, a 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).

Figure 09.06: Generalized and Specialized Transduction. 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. Specialized transduction In the lysogenic cycle, the prophage eventually excises itself from the host chromosome. Sometimes it takes a few nearby host genes and leaves a few phage genes behind. Figure 09.06: Generalized and Specialized Transduction.

Figure 09.07: A Summary of Genetic Recombination through Horizontal Gene Transfer.

Figure 09.09: FDA Approvals of New Pharmaceutical Products. 9.2 Genetic Engineering Involves the Deliberate Transfer of Genes Between Organisms Genetic engineering was born from genetic recombination. Genetic engineering involves changing the genetic material in an organism to alter its traits or products. Biotechnology is the commercial and industrial products derived from genetic engineering. Figure 09.09: FDA Approvals of New Pharmaceutical Products. Data redrawn from: Biotechnology Information Institute (http://www.biopharma.com/approvals_2010.html).

Figure 09.08: Construction of a recombinant DNA molecule. 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. Figure 09.08: Construction of a recombinant DNA molecule.

Genetic engineering has many commercial and practical applications. The genes for producing human insulin can be cloned into bacteria. Bacteria could be genetically engineered to: break down toxic wastes. produce antibiotics. Figure MI09AB: The Sequence of Steps to Engineer the Insulin Gene into Escherichia coli Cells.

Agricultural Applications Transgenic Plants have been engineered using microbial genes for: herbicidal activity. viral resistance. Figure 09.11: The Ti Plasmid as a Vector in Plant Genetic Engineering.

Figure 09.10: Developing New Products Using Genetic Engineering. Cows produce more milk when injected with bovine growth hormone produced by engineered bacteria. Figure 09.10: Developing New Products Using Genetic Engineering.

DNA Probes Can Identify a Cloned Gene or DNA Segment Specific nucleotide sequences in pathogens allow us to identify them using DNA probes. A DNA probe is a single strand DNA that recognizes and binds with a specific nucleotide sequence of the pathogen. It is used to identify HPV DNA in a Pap smear. Figure 09.12: DNA probes.

Microfocus 09.07: Biotechnology. 9.3 Microbial Genomics Studies Genes at the Single Cell to Community Levels By the end of 2011, some 2,000 microbial genomes have been sequenced. Hundreds of microbial genomes have been sequenced since the first in 1995, about 60% of which are pathogens. Microfocus 09.07: Biotechnology.

Segments of the human genome may have “microbial ancestors.” Many of the 23,000 human genes are may have come from bacteria, yeast and viruses. They were passed down from early ancestors of humans. Figure 09.13A: Genomics Activities. Modified from: Genomes Online Database

Figure 09.13B: Total number of genome sequencing projects. Microbial genomics will advance our understanding of the microbial world. Safer food production and identification of pathogens Identification of unculturable microorganisms Microbial forensics Metabolic engineering of new products Figure 09.13B: Total number of genome sequencing projects. Modified from: Genomes Online Database

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. Figure 09.14: Comparative Genomics Suggests How Microbial Genomes Can Evolve.

Figure 09.15: The process of metagenomics. Metagenomics is identifying the previously unseen microbial world. Techniques are now being developed to analyze and understand all the genomes within a microbial community. Figure 09.15: The process of metagenomics.

Future impacts of metagenomics will affect all aspects of our lives Medicine Ecology and the Environment Energy Bioremediation Biotechnology Agriculture Biodefense