11.6 How Asexual Prokaryotes Achieve Genetic Diversity
3 min read•june 18, 2024
Prokaryotes have clever ways to mix up their genes, even without sex. They can grab DNA from their surroundings, swap it with neighbors, or get it from viruses. This genetic swap meet helps them adapt quickly to new challenges.
These DNA-sharing tricks, along with other changes like mutations and gene copying, keep bacteria evolving. It's how they develop superpowers like or the ability to live in extreme places.
Mechanisms of Genetic Diversity in Asexual Prokaryotes
Transformation vs transduction vs conjugation
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- involves uptake of naked DNA from the environment released by dead cells and taken up by competent recipient cells requires for DNA uptake () and integration ()
- transfers DNA via (viruses that infect bacteria) two types: packages any bacterial DNA into phage capsid while packages specific bacterial DNA adjacent to prophage integration site
- directly transfers DNA between two living bacterial cells through cell-to-cell contact via (protein appendages) mediated by conjugative plasmids () or that integrate into the bacterial chromosome and can excise to form a conjugative
Horizontal gene transfer in prokaryotes
- allows acquisition of new genetic material from other organisms independently of vertical transmission from parent to offspring
- HGT mechanisms (, , ) enable prokaryotes to acquire beneficial genes such as antibiotic resistance () or metabolic capabilities (degradation pathways) and adapt to new environments (extreme conditions) or stressors more rapidly than by alone
- Transferred genes can be integrated into the recipient's genome or maintained on plasmids (extrachromosomal DNA elements)
- HGT facilitates spread of genetic determinants among different bacterial species and genera (Enterobacteriaceae) contributing to evolution and diversification of prokaryotic genomes over time
- , another term for HGT, plays a crucial role in prokaryotic
Transposons in bacterial evolution
- are mobile genetic elements that can move within or between genomes also known as ""
- Two main classes of :
- are simple transposons encoding only gene for movement
- Complex transposons contain additional genes such as antibiotic resistance determinants ( with kanamycin resistance)
- Transposons can:
- Insert into various locations within the genome creating insertional mutations (gene disruption)
- Cause genome rearrangements such as deletions, inversions, or duplications ()
- Mobilize adjacent genes facilitating their spread within and between genomes ()
- Transposon-mediated mutations and rearrangements contribute to bacterial genome plasticity and evolution (adaptation to new niches)
- Transposons can also carry beneficial genes such as antibiotic resistance ( with vancomycin resistance) or virulence factors () contributing to bacterial adaptation to specific niches (hospital environments) or selective pressures (antibiotic use)
- Movement and accumulation of transposons over time shape the structure and content of bacterial genomes (IS elements constitute large fractions of some genomes)
Additional mechanisms of genetic diversity
- Mutation is a primary source of genetic variation in prokaryotes, introducing changes in DNA sequences
- acts on genetic variations, favoring beneficial mutations that enhance survival and reproduction
- can lead to random changes in allele frequencies, particularly in small populations
- events can create new genes with potential for evolving novel functions
- allows for the exchange and reshuffling of genetic material, contributing to diversity
Key Terms to Review (73)
Antibiotic resistance: Antibiotic resistance is the ability of bacteria to survive and grow in the presence of drugs designed to kill them. This occurs through genetic mutations or horizontal gene transfer.
Asexual reproduction: Asexual reproduction is a mode of reproduction in which offspring are produced by a single parent without the involvement of gamete fusion. This process results in genetically identical offspring, or clones, of the parent organism.
Avery: Avery refers to Oswald Avery, a scientist whose experiments in the 1940s demonstrated that DNA is the substance that causes bacterial transformation. His work was pivotal in identifying DNA as the molecule responsible for heredity.
Bacteriophages: Bacteriophages are viruses that infect and replicate within bacteria. They play a crucial role in bacterial genetics and microbial diversity.
Beta-Lactamases: Beta-lactamases are enzymes produced by bacteria that confer resistance to beta-lactam antibiotics, such as penicillins and cephalosporins, by hydrolyzing the beta-lactam ring and rendering the antibiotics ineffective. These enzymes play a crucial role in the ability of bacteria to achieve genetic diversity, develop drug resistance, and exhibit virulence factors.
Clostridium botulinum: Clostridium botulinum is a Gram-positive, anaerobic bacterium known for producing the neurotoxin botulinum. This toxin causes botulism, a severe and potentially fatal illness.
Competence Factors: Competence factors are molecular signals and mechanisms that allow certain prokaryotic cells to become competent, or capable of taking up extracellular DNA from their environment. This process is a key way that asexual prokaryotes can achieve genetic diversity without sexual reproduction.
Competence Proteins: Competence proteins are a group of specialized proteins involved in the process of genetic transformation, which allows asexual prokaryotes to acquire new genetic material from the environment and incorporate it into their own genome. These proteins facilitate the uptake, transport, and integration of exogenous DNA, contributing to the genetic diversity of asexual prokaryotes.
Composite Transposons: Composite transposons are a type of genetic element found in bacteria and other prokaryotes that can move and replicate within the genome. They are composed of two or more distinct transposable elements, typically including a central antibiotic resistance gene flanked by insertion sequences, which allow the entire unit to transpose as a single entity.
Conjugation: Conjugation is a process where genetic material is transferred between bacterial cells through direct contact. It often involves the formation of a pilus to facilitate the exchange of plasmids.
Conjugation: Conjugation is a process of genetic exchange between two prokaryotic cells, typically bacteria, where genetic material is transferred from one cell to another. This process allows for the sharing of genetic information and the acquisition of new traits, contributing to the genetic diversity of asexual prokaryotes.
Conjugation pilus: A conjugation pilus is a hair-like appendage found on the surface of many bacteria. It facilitates the transfer of genetic material between bacterial cells during conjugation.
Corynebacterium diphtheriae: Corynebacterium diphtheriae is a Gram-positive, non-motile bacterium that causes diphtheria, a serious respiratory disease. It produces a potent exotoxin that inhibits protein synthesis in host cells.
Donor cell: A donor cell is a prokaryotic cell that provides genetic material to a recipient cell during processes like conjugation, transformation, or transduction. This exchange contributes to genetic diversity in asexual organisms.
E. coli: Escherichia coli (E. coli) is a gram-negative, rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms. While most strains are harmless, some can cause serious food poisoning and infections.
F pilus: An F pilus, or sex pilus, is a hair-like appendage found on the surface of many bacteria that facilitates the transfer of DNA between cells during bacterial conjugation. It is primarily composed of the protein pilin and encoded by the F (fertility) plasmid.
F plasmid: The F plasmid, or fertility plasmid, is a circular piece of DNA that enables bacteria to transfer genetic material through conjugation. It contains genes that code for the formation of a pilus and other proteins essential for this process.
F Plasmid: An F plasmid, also known as the fertility factor, is a type of extrachromosomal genetic element found in certain bacteria. It is a circular, double-stranded DNA molecule that can replicate independently of the host chromosome and is responsible for the conjugation process, allowing for the horizontal transfer of genetic material between bacterial cells.
F’ plasmid: An F’ (F prime) plasmid is a type of plasmid in bacteria that carries extra genes in addition to the fertility factor (F factor). These extra genes can be transferred between bacteria, facilitating genetic diversity.
F+ cell: An F+ cell is a bacterial cell that contains the F (fertility) plasmid, which allows it to form a conjugation pilus and transfer genetic material to an F- cell. This process contributes to genetic diversity in bacterial populations.
F− cell: An F− cell is a bacterial cell that lacks the F (fertility) plasmid, which means it cannot initiate conjugation. It can receive genetic material from an F+ or Hfr cell during the process of bacterial conjugation.
Fertility factor: The fertility factor (F factor) is a plasmid in bacteria that enables the transfer of genetic material through conjugation. It plays a crucial role in genetic diversity among prokaryotes.
Gene Duplication: Gene duplication is a genetic event where a DNA sequence is duplicated, resulting in the presence of two or more identical or highly similar genes within the same genome. This process is a key mechanism by which asexual prokaryotes can achieve genetic diversity, as it allows for the creation of new genetic material that can then undergo further mutations and adaptations.
Generalized transduction: Generalized transduction is a process by which bacteriophages transfer bacterial DNA from one bacterium to another during infection. This mechanism can result in genetic recombination in the recipient bacteria.
Generalized Transduction: Generalized transduction is a process in which any bacterial DNA can be packaged into a bacteriophage (viral) particle and transferred to another bacterial cell, allowing for the exchange of genetic material between unrelated bacteria. This mechanism contributes to the genetic diversity of asexual prokaryotes.
Genetic diversity: Genetic diversity refers to the variety of genetic material within a population of organisms. In microbiology, this is crucial for the adaptability and survival of microbial species.
Genetic Drift: Genetic drift is a random process that occurs in small populations, where certain alleles can become more or less frequent over generations due to chance events, rather than natural selection. It is one of the key mechanisms by which asexual prokaryotes, such as bacteria, can achieve genetic diversity in the absence of sexual reproduction.
Genetic Recombination: Genetic recombination is the process by which genetic material from two different sources is combined to create a new, genetically distinct individual. This process is crucial for increasing genetic diversity within asexual prokaryotic organisms.
Genome Plasticity: Genome plasticity refers to the ability of a prokaryotic organism's genome to undergo structural and functional changes in response to various environmental and genetic factors. This dynamic nature of the genome allows asexual prokaryotes to achieve genetic diversity without the need for sexual reproduction.
Griffith: Griffith refers to Frederick Griffith, a British bacteriologist who discovered the phenomenon of bacterial transformation in 1928. His experiments with Streptococcus pneumoniae provided the first evidence that genetic material could be transferred between bacteria.
Hemolytic uremic syndrome: Hemolytic uremic syndrome (HUS) is a serious condition characterized by the destruction of red blood cells, leading to kidney failure. It is often caused by infection with Shiga toxin-producing bacteria, such as Escherichia coli O157:H7.
Hfr cell: Hfr cell (High-frequency recombination cell) is a bacterium with a conjugative plasmid integrated into its chromosomal DNA. It facilitates the transfer of genetic material to another bacterium through conjugation.
Horizontal gene transfer (HGT): Horizontal gene transfer (HGT) is the movement of genetic material between organisms other than through vertical inheritance (parent to offspring). This process contributes significantly to genetic diversity in prokaryotes.
Horizontal Gene Transfer (HGT): Horizontal gene transfer (HGT) is the transfer of genetic material between organisms other than via vertical transmission (reproduction). It is a key mechanism by which asexual prokaryotes, such as bacteria, can achieve genetic diversity without the need for sexual reproduction.
Insertion Sequences (IS Elements): Insertion sequences (IS elements) are short, mobile DNA sequences found in the genomes of prokaryotes that can insert themselves into new locations within the host's DNA, contributing to genetic diversity through insertional mutagenesis and genome rearrangements.
Integrative Conjugative Elements (ICEs): Integrative Conjugative Elements (ICEs) are mobile genetic elements found in bacteria and archaea that can integrate into the host's genome and be transferred to other cells through conjugation, a process of direct cell-to-cell DNA transfer. ICEs play a crucial role in how asexual prokaryotes achieve genetic diversity.
IS-mediated recombination: IS-mediated recombination is a process by which insertion sequences (IS) in the genome of asexual prokaryotes can facilitate genetic diversity through the rearrangement and exchange of genetic material. This mechanism allows prokaryotes to adapt and evolve without the need for sexual reproduction.
Jumping genes: Jumping genes, also known as transposons, are DNA sequences that can change their position within a genome. They play a significant role in genetic diversity and evolution.
Lateral Gene Transfer: Lateral gene transfer, also known as horizontal gene transfer, is the transfer of genetic material between organisms other than via the vertical transmission from parent to offspring. This process allows prokaryotes, such as bacteria, to acquire new traits and genetic diversity without sexual reproduction.
McCarty: Colin Munro MacLeod, Oswald Avery, and Maclyn McCarty are credited with proving that DNA is the substance that causes bacterial transformation. Their groundbreaking work established DNA as the material of inheritance.
McClintock: Barbara McClintock was an American scientist who won the Nobel Prize in Physiology or Medicine in 1983 for discovering genetic transposition, or 'jumping genes.' Her work with maize demonstrated that genes could change positions on chromosomes, influencing gene expression and mutation.
Meiosis: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in four genetically diverse haploid cells. It is crucial for sexual reproduction and genetic diversity in eukaryotic organisms.
Mutation: Mutation is a permanent change in the DNA sequence of a gene or chromosome that can alter the genetic information and lead to changes in the structure or function of the organism. Mutations are a key driver of genetic diversity and evolution in both sexual and asexual organisms.
Natural Selection: Natural selection is the process by which certain traits become either more or less common in a population over time. It is the fundamental mechanism of evolution, as it allows organisms with advantageous traits to survive and reproduce, passing on those traits to future generations.
Pathogenicity Islands: Pathogenicity islands are specialized regions of the bacterial genome that contain clusters of genes encoding virulence factors. These genetic elements play a crucial role in the ability of pathogenic bacteria to infect and cause disease in their hosts, connecting the concepts of how asexual prokaryotes achieve genetic diversity and the virulence factors that contribute to bacterial and viral pathogenesis.
Plasmid: A plasmid is a small, circular piece of DNA that exists independently of the chromosomal DNA in prokaryotic cells. Plasmids often carry genes that confer advantageous traits such as antibiotic resistance.
R plasmids: R plasmids are extrachromosomal DNA molecules found in bacteria that carry genes responsible for antibiotic resistance. They can be transferred between bacteria through horizontal gene transfer, contributing to genetic diversity and the spread of antibiotic resistance.
Recipient cell: A recipient cell is a bacterial cell that receives genetic material from a donor cell during processes such as transformation, transduction, or conjugation. This transferred genetic material can lead to increased genetic diversity and new traits.
Recombinant DNA: Recombinant DNA is a form of artificial DNA that is created by combining two or more sequences that would not normally occur together. It is often used in genetic engineering to manipulate genes for research, medicine, and biotechnology.
Recombination Enzymes: Recombination enzymes are a class of enzymes that facilitate the process of genetic recombination, which is a crucial mechanism by which asexual prokaryotes, such as bacteria, achieve genetic diversity. These enzymes catalyze the exchange and rearrangement of genetic material between DNA molecules, enabling the creation of new genetic combinations.
Rolling circle replication: Rolling circle replication is a process of DNA replication in circular DNA molecules where a nick in one strand allows the 3' end to serve as a primer for synthesis. It produces multiple linear copies of the circular DNA, which can be used for various cellular processes.
Salmonella pathogenicity islands: Salmonella pathogenicity islands (SPIs) are distinct genetic regions in the Salmonella genome that encode various virulence factors. These regions are crucial for the bacteria's ability to cause disease and adapt to different environments.
Sex Pili: Sex pili, also known as conjugation pili or F pili, are specialized appendages found on the surface of some bacterial cells that facilitate the transfer of genetic material between cells during a process called conjugation. These pili act as conduits, allowing the direct exchange of DNA between donor and recipient cells, thereby increasing genetic diversity in asexual prokaryotic populations.
Sexual reproduction: Sexual reproduction involves the combination of genetic material from two parent organisms to create offspring with genetic diversity. This process typically includes meiosis and fertilization.
Shigella: Shigella is a genus of Gram-negative bacteria known for causing shigellosis, a severe form of dysentery. It primarily affects the gastrointestinal tract by invading and destroying the epithelial cells lining the intestines.
Specialized transduction: Specialized transduction is a process where a bacteriophage transfers specific portions of the bacterial genome to another bacterium. This occurs during the lysogenic cycle when prophage excision includes adjacent bacterial genes.
Specialized Transduction: Specialized transduction is a type of genetic recombination in bacteria where a bacteriophage (virus that infects bacteria) incorporates a small segment of the host's DNA into its own genome and then transfers that genetic material to a new bacterial host during the viral infection process. This allows for the exchange of genetic information between bacteria and can contribute to the acquisition of new traits, such as antibiotic resistance or virulence factors.
Streptococcus pneumoniae: Streptococcus pneumoniae is a Gram-positive bacterium often found in the human respiratory tract, capable of causing diseases such as pneumonia, meningitis, and sinusitis. It exhibits virulence factors like a polysaccharide capsule that help it evade the immune system.
Tn1546: Tn1546 is a transposon, a mobile genetic element capable of moving within and between bacterial genomes. It is a key contributor to the genetic diversity observed in asexual prokaryotes, as it facilitates the transfer of genetic material between different bacterial species or strains.
Tn5: Tn5 is a transposon, a mobile genetic element that can insert itself into the DNA of a host organism, often used as a tool in molecular biology to introduce genetic modifications. It is particularly important in the context of how asexual prokaryotes, such as bacteria, achieve genetic diversity.
Transduction: Transduction is the process by which bacterial DNA is transferred from one bacterium to another via a bacteriophage. It plays a significant role in horizontal gene transfer and genetic diversity among prokaryotes.
Transduction: Transduction is the process by which genetic material is transferred from one organism to another through the action of a virus or viral vector. This process can have significant implications in the context of viral life cycles, genetic diversity in asexual prokaryotes, genetic engineering, and the development of drug resistance.
Transformation: Transformation is the genetic alteration of a prokaryotic cell resulting from the direct uptake and incorporation of exogenous genetic material. This process allows for genetic diversity in asexual prokaryotes.
Transformation: Transformation is the process by which genetic material, such as DNA, is introduced into a cell, allowing the cell to acquire new genetic traits or characteristics. This process is a fundamental concept in microbiology and genetic engineering, as it enables the modification and manipulation of the genetic makeup of organisms.
Transposase: Transposase is an enzyme that facilitates the movement of transposable elements (TEs) within the genome. It catalyzes the cut-and-paste mechanism by which these genetic elements are excised from one location and inserted into another.
Transposase: Transposase is an enzyme that facilitates the movement of DNA sequences called transposons or 'jumping genes' within and between genomes. It plays a crucial role in how asexual prokaryotes, such as bacteria, achieve genetic diversity through the process of transposition.
Transposition: Transposition is the process by which a DNA sequence, known as a transposable element, can change its position within the genome. This can result in mutations and contribute to genetic diversity.
Transposons: Transposons, also known as jumping genes, are DNA sequences that can change their position within the genome. They play a significant role in genetic diversity and evolution by causing mutations and altering the cell's genetic identity.
Transposons: Transposons, also known as 'jumping genes', are DNA sequences that can move and replicate within a genome, contributing to genetic diversity in asexual prokaryotes. They are capable of inserting themselves into new locations on the chromosome, potentially disrupting or altering the expression of nearby genes.
Vertical gene transfer: Vertical gene transfer is the transmission of genetic material from parent to offspring during reproduction. It ensures the continuity of genetic information across generations.
Virulence factor: A virulence factor is a molecule or structure produced by a pathogen that contributes to its ability to cause disease. These factors enable the pathogen to invade the host, evade the immune system, and obtain nutrients from the host.
Virulence gene: A virulence gene is a gene that encodes factors enabling a microorganism to establish an infection, cause disease, or evade host defenses. These genes contribute to the pathogenicity of the organism.
VTEC: VTEC (Verotoxin-producing Escherichia coli) are a group of E. coli bacteria that produce toxins called verotoxins or Shiga-like toxins. These bacteria can cause severe foodborne illness in humans.