selective pressure

Examples of selective pressure in the following topics:

• Shared Features of Bacteria and Archaea

  • Gupta has proposed that the Archaea evolved from Gram-positive bacteria in response to antibiotic selection pressure.
  • His proposal is that the selective pressure towards resistance generated by the Gram-positive antibiotics was eventually sufficient to cause extensive changes in many of the antibiotics' target genes, and that these strains represented the common ancestors of present-day Archaea.
  • The evolution of Archaea in response to antibiotic selection, or any other competitive selective pressure, could also explain their adaptation to extreme environments (such as high temperature or acidity) as the result of a search for unoccupied niches to escape from antibiotic-producing organisms; Cavalier-Smith has made a similar suggestion.

• Bacterial Genomes

  • One theory predicts that bacteria have smaller genomes due to a selective pressure on genome size to ensure faster replication.
  • Deletional bias selection is but one process involved in evolution.
  • Continually, further selective pressure is evident as free-living bacteria must produce all gene-products independent of a host.
  • Given that there is sufficient opportunity for gene transfer to occur and there are selective pressures against even slightly deleterious deletions, it is intuitive that free-living bacteria should have the largest bacterial genomes of all bacteria types.
  • As such, in recently formed and facultative parasites, there is an accumulation of pseudogenes and transposable elements due to a lack of selective pressure against deletions.

• Compromised Host

  • Furthermore, patients are often prescribed antibiotics and other antimicrobial drugs to help treat illness; this can increase the selection pressure for the emergence of resistant strains.

• Elements of Life

  • Selection pressures for catalytic efficiency and diversity might have resulted in ribozymes which catalyse peptidyl transfer (hence formation of small proteins), since oligopeptides complex with RNA to form better catalysts.

• Emergence of Viral Pathogens

  • A longer epidemic allows for selection pressure to continue over an extended period of time and stronger host immune responses increase selection pressure for the development of novel antigens.

• Gas Vesicles

  • Because the gas vesicle is a hollow cylinder, it is liable to collapse when the surrounding pressure becomes too great.
  • Natural selection has fine-tuned the structure of the gas vesicle to maximize its resistance to buckling by including an external strengthening protein, GvpC, rather like the green thread in a braided hosepipe.
  • There is a simple relationship between the diameter of the gas vesicle and pressure at which it will collapse - the wider the gas vesicle the weaker it becomes.
  • Deep lakes that experience winter mixing will expose the cells to the hydrostatic pressure generated by the full water column.
  • This will select for species with narrower, stronger gas vesicles.

• Osmotic Pressure

  • Osmotic pressure is the pressure which must be applied to a solution to prevent the inward flow of water across a semipermeable membrane.
  • Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane.
  • It is also defined as the minimum pressure needed to nullify osmosis.The phenomenon of osmotic pressure arises from the tendency of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute to which the membrane is impermeable.
  • This process is of vital importance in biology as the cell's membrane is selective toward many of the solutes found in living organisms.
  • Removal of water and addition of salt to meat creates a solute-rich environment where osmotic pressure draws water out of microorganisms, thereby retarding their growth.

• Regulating Virulence

  • Virulence regulation is a combination of the specific traits of the pathogen and the evolutionary pressures that lead to virulent traits.
  • Virulence can be understood in terms of proximate causes—those specific traits of the pathogen that help make the host ill—and ultimate causes—the evolutionary pressures that lead to virulent traits occurring in a pathogen strain.
  • If the pathogen's virulence kills the host and interferes with its own transmission to a new host, virulence will be selected against.
  • But it is selection in the bacterium's normal life cycle in the soil that leads it to produce this toxin, not any evolution with a human host.

• High Pressure

  • Under very high hydrostatic pressure(HHP) of up to 700 MPa, water inactivates pathogens such as E. coli and Salmonella.
  • High pressure processing (HPP), pascalization or bridgmanization, is a method of preserving and sterilizing food, in which a product is processed under very high pressure, leading to the inactivation of certain microorganisms and enzymes in the food.
  • Around 1970, researchers renewed their efforts in studying bacterial spores after it was discovered that using moderate pressures was more effective than using higher pressures.
  • When subjected to moderate pressures, bacterial spores germinate, and the resulting spores are easily killed using pressure, heat, or ionizing radiation.
  • The pumps may apply pressure constantly or intermittently.

• Clonal Selection and Tolerance

  • Clonal selection and tolerance select for survival of lymphocytes that will protect the host from foreign antigens.
  • Clonal selection occurs after immature lymphocytes express antigen receptors.
  • The preservation of useful specificities is called positive selection.
  • Negative selection of developing lymphocytes is an important mechanism for maintaining central tolerance.
  • clonal selection of the B and T lymphocytes:1.