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Related Concept Videos

Types of Selection01:46

Types of Selection

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Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
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Antibiotic resistance in bacteria arises when microorganisms evolve the ability to withstand drugs designed to kill them or inhibit their growth, rendering once-effective treatments useless. This phenomenon, driven by genetic change and selection under antibiotic exposure, poses a profound threat to modern medicine. Mechanisms include drug-inactivating enzymes (e.g., β-lactamases), efflux pumps that eject antibiotics, mutations altering antibiotic targets, decreased drug uptake, and...
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Regulation of Bacterial Virulence01:28

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Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...
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Frequency-dependent Selection01:21

Frequency-dependent Selection

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When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.
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Evolution of Microbial Genome01:08

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Microbial genome evolution is a highly dynamic process shaped by continual gene gain and loss across species and strains. This genomic flexibility allows microorganisms to adapt rapidly to environmental pressures and interactions with other organisms. Central to understanding this diversity is the distinction between the core and pan genomes.The core genome comprises the genes shared by all sampled strains of a species, representing essential functions needed for fundamental cellular processes.
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Related Experiment Video

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Constructing Mutants in Serotype 1 Streptococcus pneumoniae strain 519/43
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Selective and genetic constraints on pneumococcal serotype switching.

Nicholas J Croucher1, Lisa Kagedan2, Claudette M Thompson2

  • 1Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom; Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, United States of America.

Plos Genetics
|April 1, 2015
PubMed
Summary

Streptococcus pneumoniae serotype switching is enriched within serogroups, suggesting selection for conserved capsule serogroups. Host immunity may drive this pattern, not just genetic or physiological factors.

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Area of Science:

  • Microbiology
  • Genetics
  • Immunology

Background:

  • Streptococcus pneumoniae possesses over 90 distinct polysaccharide capsule serotypes, grouped into serogroups.
  • Serotype switching, altering capsule type via recombination in the capsule polysaccharide synthesis (cps) locus, is a known phenomenon.

Purpose of the Study:

  • To investigate the frequency and mechanisms of serotype switching in Streptococcus pneumoniae.
  • To determine the selective pressures driving observed serotype distributions.

Main Methods:

  • Analysis of 616 whole genome sequences from pneumococcal carriage surveys.
  • Characterization of 20 "serotype switching" events.
  • Phenotypic analysis of engineered bacterial strains.

Main Results:

  • A significant enrichment (p < 0.0001) of within-serogroup serotype switches was observed.
  • Within-serogroup switches did not always involve the entire cps locus, unlike between-serogroup switches.
  • Genetic and physiological hypotheses could not fully explain the observed distribution of serotypes.

Conclusions:

  • The observed pattern of serotype switching suggests selection for maintaining serogroup identity.
  • Host immunity targeting multiple serotypes within a serogroup is a potential driving force for this selection.
  • Further research should explore immunological mechanisms shaping pneumococcal capsule diversity.