Microorganisms, particularly bacteria, are extensively utilized in laboratory settings due to their rapid growth, minimal space requirements, and ease of manipulation. A common laboratory strain of E. coli is often used for genetic studies, as it has been modified to be non-pathogenic. The process of culturing bacteria begins with plating, where a liquid culture of bacteria is spread onto a petri dish containing agar, a gelatinous substance that provides a solid medium for growth. As bacteria divide asexually, they form visible clusters known as colonies, which consist of genetically identical cells derived from a single ancestor.
Bacteria can be classified based on their nutritional requirements into two categories: prototrophic and auxotrophic. Prototrophic bacteria, often referred to as wild type, can grow on minimal media, which contains basic nutrients such as salts and carbon. In contrast, auxotrophic bacteria require additional specific nutrients due to mutations that prevent them from synthesizing essential compounds. These mutants are typically denoted with a minus sign, while prototrophs are indicated with a plus sign.
The bacterial chromosome serves as the primary DNA molecule, containing essential genes necessary for survival and reproduction. Additionally, bacteria possess plasmids, which are small, circular DNA molecules that carry non-essential genes. These plasmids can confer advantageous traits, such as antibiotic resistance, and contribute to bacterial diversity and adaptability. For instance, E. coli can harbor up to 270 different plasmids, each potentially influencing its phenotype and environmental resilience.
Mutations in bacterial DNA can manifest phenotypically, affecting colony morphology, size, and resistance to antibiotics. Scientists often observe these changes to understand bacterial behavior and evolution. Bacterial DNA can be transferred between cells through three primary mechanisms: conjugation, transformation, and transduction. Conjugation involves direct contact between two bacterial cells, allowing DNA transfer through a specialized structure. Transformation occurs when a bacterium absorbs free DNA from its environment, while transduction involves the transfer of DNA via bacteriophages, viruses that infect bacteria. These processes exemplify horizontal gene transfer, contrasting with vertical transmission, where DNA is passed from parent to offspring during cell division.
Understanding these mechanisms is crucial for studying bacterial genetics, evolution, and their roles in various ecological and medical contexts.
