Genetic Study of Bacteria and Bacteriophage

Abstract

AbstractBacterial genomes are made up of a circular chromosome that possesses a single-stranded DNA (ssDNA) molecule of several million base pairs in total length. A classic example is E. coli genome that is widely organized in approximately 4.6 million base pairs of DNAs. No wonder that some bacteria contain multiple chromosomes, for example, Vibrio cholerae that causes cholera has two circular chromosomes and Rhizobium meliloti has three chromosomes. Apart from this composition, there are few bacteria that do not carry circular DNA and instead carry a linear chromosome. In addition to its own genome, the bacterial genome also possesses an additional structure known as “plasmid”—a small circular DNA molecule present in many numbers (usually known as copy number). Plasmids accommodate genes that are not essential at the functional point of view for bacteria but that might have been involved as an important factor for the life cycle and growth of their bacterial hosts. Some plasmids are involved in the mating process between bacteria (provide a channel for the exchange of genetic material during mating, which will be discussed in the next section). Some plasmid leads to an important role in the generation of antibiotic resistance among the population. Most plasmids are circular and of several thousand base pairs in length and, however, some of small size; about a hundred base pairs in the length have been found. Each plasmid structure carries at least an origin of replication (ori), a start point for DNA replication. The main function of ori is to let the plasmid replicate independently without involving a bacterial chromosome. Episomes are plasmids that are capable of freely replicating and integrating into the bacterial chromosomes. Episomes are categorized into several types based on importance and functionality. The F (fertility) factor of E. coli is one type of episome found robustly. F factor basically regulates the mating and gene exchange between E. coli cells (which will be discussed in the next section). In this part, we have focused on the bacterial mutant gene mutation process that contributes to genetic variation in the bacterial population. We begin with an overview of the chemical nature of the mutation in bacterial genetics and its effect at both molecular and organismal levels.