Mutant Selection

Mutation is a rare occurrence. Mutagens barely affect the procedure. Finding them is a difficulty for scientists. In the isolation of mutants, there are two techniques used. The direct and indirect selections are these. Researchers put a substrate that allows mutations to grow in the direct selection. It prevents the parent's growth. For instance, by inoculating all cells in a medium that contains antibiotics, mutants that are resistant to antibiotics can be selected. To form colonies, only immune cells are still present. Auxotrophic mutants are separated from prototrophic parent strains through indirect selection. This process is more difficult. This is so that the media used can also assist parental development. It is also termed as adverse selection. It identifies mutants, which have lost ability to work as the parent strains. Scientists identify mutants by replica plating. The method was developed to allow copying of patterns of growth from a plate to another. The method utilizes fabrics like velveteen, which allow transfer without interfering with spatial relationships. It helps in detecting biochemical mutants. This approach is also applied when scientists want to determine antibiotic sensitivity (Anderson, Salm, Allen, & Nester, 2016).

DNA- Mediated Transformation

The process of transformation involves uptake of naked DNA by the recipient cells. Naked DNA is not confined to virus cell surrounding. Confined DNA cannot be transformed because the surrounding medium contains DNAse. This enzyme prevents transformation. The origin of naked DNA can be a burst cell or cells that secrete DNA. When these cells burst, long chromosomes are released. They break into many pieces. Bacterial cells secrete DNA as a way of promoting transformations. Competence of cells matter in conversion. They should be in a healthy physiological state to allow uptake of DNA. Most of the competent bacterial cells can receive the genetic component. The source does not matter. A few species will be limited to absorption from related bacteria. Some species retain competence at all times. Others do so in specific conditions like the critical density of the population or shortage of nutrient supply. The particular nature of uptake shows that the cells quickly sense their surroundings. They can adjust their behaviors quickly. In transformation, double-stranded DNA clings to a competent cell. One strand finds its way into the cell. The other stand becomes degraded. The strand that finds its way inside integrates into the genome of the recipient cell. The process is referred to as homologous recombination. DNA replicates, and cell division follows. Transformed cells can multiply in controlled conditions. They grow to form colonies. Cells, which do not undergo a transformation, die (Anderson, Salm, Allen, & Nester, 2016).

Transduction

Phages transfer genes from donor to recipient. Transduction can be specialized or generalized. Generalized transduction transfers any gene. Specialized transduction transfers specific genes. The Phages have genetic material. It can either be RNA or DNA. The genetic material is surrounded by a protein coat. Phage infects bacterium when it attaches itself to it. It affects the nucleic acid in that cell. Specially encoded enzymes divide DNA into smaller pieces. Enzymes in bacterial cells replicate the nucleic acid in the phage. Proteins that are important in making phage are synthesized. The nucleic acid then enters into the coat. All components assemble to make complete particles. Once all components are assembled, new bacteriophages become released by lysis of the host cell. Phage particles attach on bacterial cells and continue the infection cycle (Anderson, Salm, Allen, & Nester, 2016).



Conjugation

Conjugation is quite complex. It requires the contact of recipient and donor. Gram-negative and gram-positive cells can transfer by this method. The process is different in both groups. Scientists have had intensive studies on gram-negative bacteria. Chromosomal and plasmid DNA is transferred between cells. Plasmids are frequently transferred by conjugation. Conjugate plasmids transfer involves several steps. These are making contact, initiating the transfer, transferring DNA and completion of the transfer. In the first step, donor cells bind to specific receptors. After initial contact, F pillars retracts for the synthesis of the complementary strand. The remaining strand serves in DNA synthesis. When the transfer is complete, cells act as donors (Anderson, Salm, Allen, & Nester, 2016).

Prions and Viroids

These are infectious agents, which have a simpler structure. Viroids have a one-strand RNA molecule. It forms a closed ring. They have a tiny size. Viroids mostly infect plants. They are the causative agents of serious diseases. They find their way in a plant through a wound site. They do not bind to a particular receptor. Prions solely have proteins. They are associated with several fatal human diseases. They also cause animal diseases. Protein accumulates in the neural. These neurons die. The function of brain deteriorates. The affected tissues develop holes. Prions accumulate in tissues causing disease. The shape of proteins differs between healthy proteins and proteins in infectious cells. Proteins of infectious cells do not degrade quickly. They resist chemical and heat treatments. The disease is transmitted between organisms of the same species (Anderson, Salm, Allen, & Nester, 2016).



Bacterial Defenses against Phages

Bacterial phages have a lot of impact on the immune system. Predatory bacteria phages thrive in the same environment as bacteria. Bacteria has evolved mechanistically to survive attacks from the bacterial phages. Bacterial Phages will rapidly evolve to get rid of the defenses. Successful infection begins when the virus is adsorbed to a particular receptor. They do not remain on the cell surface. They access all areas for spatial distribution. Cells have strategies of preventing adsorption. These include modification of the recipient structure. This is through concealing receptors and mutation. Receptor availability is reduced through a reduction in receptor expression. This is reversible switching, which allows heterogeneity in the population. This is an effort of seeking survival. Bacteria may also produce decoys. Membrane vesicles on the outer section reduce levels of phages. Shedding vesicles in the surrounding is one way of preventing phage adsorption (Anderson, Salm, Allen, & Nester, 2016).

Bacteria can also block DNA entry. Once the phage attaches to suitable receptors, systems of super-infection exclusion prevent the injection of bacteriophages into the host. Their system also protects the host from being infected by related bacteriophages. Super-infection systems are typically protein membranes. These systems provide a selective advantage to the bacterium. They confront all phage superinfection. They also protect the surrounding population. The targeted phage cannot infect the surrounding cells (Anderson, Salm, Allen, & Nester, 2016).

There are mechanisms to get rid of bacteriophages that inject their DNA in the bacterium. Several natural defenses prevent replication and release of phages. Restriction-modification system destroys the invading DNA. Abortive infection is another defense mechanism. This system leads to the death of the infected cells. This is a sacrifice to safeguard the surrounding from predation. Genetic elements typically encode abortive infection systems. These include plasmids and phages. The systems are diverse. They can act in any phage development stage. Their purpose is to eliminate production of viruses. Gram-positive bacteria have parasites, which interfere with the reproduction of bacteriophages. S. Aureus pathogenicity islands disseminate virulence factors. These factors reside in the bacterial chromosome. They are induced to replicate themselves in times of infection. Pathogenicity islands may remodel capsid protein to smaller capsids. Bacteria has been able to overcome the selective pressure of bacteriophages. They resist pressure by controlling number and composition of bacteriophages. Bacteria has selfish elements which provide barriers to infection. In most cases, the changes do not compromise physiological functions of the host cell (Anderson, Salm, Allen, & Nester, 2016).























References

Anderson, D., Salm, S., Allen, D., & Nester, E. (2016). Nester's Microbiology: A Human Perspective. New York: Mc Graw-Hill Education.