Molecular Genetics of Microbes


Learning Outcomes

On completion of the module students should:
● Appreciate the mechanistic basis and biological significance of genetic exchange between bacteria
● Be able to construct physical and genetic maps from experimental data
● Be conversant with some of the powerful genetic tools that have been developed for analysing biological processes
● Be familiar with the genetic systems of both Gram-negative and Gram-positive bacteria
● Appreciate how bacteria respond to environmental changes


This module is an integrated series of lectures, practical classes and data interpretation workshops dealing with the genetics of bacteria and their viruses. Both classical and molecular genetic techniques are covered; their use as powerful tools for the investigation of a variety of phenomena of general biological interest is emphasised.


The module comprises four interconnected parts. It begins with a discussion of the ways in which bacteria respond to different mutagenic agents, which leads on to a consideration of the processes they employ to repair damaged DNA. Genetic exchange (transformation, transduction and conjugation) is then dealt with in detail, after which the main events underlying homologous recombination are analysed. This usually accompanies genetic exchange and is involved in certain types of DNA repair. Finally, the use of mutagenesis and genetic exchange for the analysis of a metabolic pathway is illustrated.

Next, we deal with the biology of plasmids and their use in genetic engineering. The mechanisms whereby plasmids replicate and are transmitted from cell to cell are explored, as are those involved in determining plasmid copy number and compatibility. Transposable elements are commonly found on plasmids and their utility for undertaking genetic analysis is analysed. Mechanisms of transposition are discussed and this leads finally to a consideration of processes of illegitimate and site-specific recombination. Finally we explore the use of transposable elements and reporter genes for investigating gene expression.

There follows an in depth analysis of the bacterial cell cycle with special emphasis on the experimental approaches that have been employed to dissect the mechanisms of DNA replication and cell division. We then turn to bacteriophage lambda, which has alternative, lytic or lysogenic, lifestyles. The choice between these two contrasting modes of virus multiplication is determined by an environmentally responsive genetic switch, the nature of which is analysed in detail.

Finally, we explore some of the many different ways in which bacteria respond to changes in their environment. In one case (chemotaxis) this leads to a purposeful change in their spatial location (essentially a behavioural response). In another (endospore development) this leads to a temporally controlled programme of compartmentalised gene expression, the complexities of which are still being unravelled today. Lastly, we discuss the regulation of virulence gene expression, by focusing on how pathogenic microbes integrate information about their plant or animal host environment. The roles of two-component regulators and quorum sensing molecules in signal integration will be compared. This last part of the module illustrates the analytical power of genetic approaches for investigating biological problems.