bacterial conjugation

Examples of bacterial conjugation in the following topics:

• Pili and Pilus Assembly

  • The terms pilus and fimbria (Latin for "thread" or "fiber," plural: fimbriae) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation.
  • Conjugative pili allow the transfer of DNA between bacteria, in the process of bacterial conjugation.
  • Not all bacteria can make conjugative pili, but conjugation can occur between bacteria of different species.
  • Bacterial type IV pilins are similar in structure to the component flagellins of Archaeal flagella.
  • A schematic drawing of bacterial conjugation.

• Type III and Type IV Secretion

  • Type III and IV secretion systems are utilized by pathogenic bacteria to transfer molecules from the bacterial cell to the host cell.
  • Type III secretion systems are characterized by the ability to inject a protein directly from the bacterial cell to the eukaryotic cell.
  • Type IV secretion systems are characterized by the ability to transfer secretory molecules via a mechanism similar to the bacterial conjugation machinery.
  • The bacterial conjugation machinery allows transfer of genetic material to occur via direct cell-to-cell contact or by a bridge-like apparatus between the two cells.
  • Type IV secretion systems are characterized by the ability to transfer material using machinery similar to the bacterial conjugation machinery.

• Chromosomes and DNA Replication in the Archaea

  • Plasmids may be transferred between cells by physical contact, in a process that may be similar to bacterial conjugation.
  • This process in Archaea appears to be similar to both bacterial and eukaryotic systems.
  • However, the proteins involved that direct cell division are similar to those of bacterial systems.
  • The primase used to synthesize a short RNA primer from the free 3'OH group varies in Archaea when compared to that of bacterial and eukaryotic systems.

• Phenotypic Analysis

  • Most microorganisms can reproduce rapidly, and microbes such as bacteria can also freely exchange genes through conjugation, transformation, and transduction, even between widely-divergent species.
  • Classification seeks to describe the diversity of bacterial species by naming and grouping organisms based on similarities.
  • These plasmids can be transferred between cells through bacterial conjugation.
  • While bacterial cell membranes are made from phosphoglycerides with ester bonds, archaean membranes are made of ether lipids.
  • While these schemes allowed the identification and classification of bacterial strains, it was unclear whether these differences represented variation between distinct species or between strains of the same species.

• Vectors for Genomic Cloning and Sequencing

  • Insertion of a vector into the target cell is usually called transformation for bacterial cells, and transfection for eukaryotic cells, although the insertion of a viral vector is often called transduction.
  • Plasmids may be conjugative / transmissible and non-conjugative.
  • Conjugative vectors mediate DNA transfer through conjugation and therefore spread rapidly among the bacterial cells of a population, such as the F plasmid, as well as many R and some col plasmids.
  • Non-conjugative vectors do not mediate DNA through conjugation, such as many R and col plasmids.

• Bacterial Transformation

  • Transformation is one of three processes by which exogenous genetic material may be introduced into a bacterial cell; the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact), and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium).
  • Bacterial transformation may be referred to as a stable genetic change, brought about by the uptake of naked DNA (DNA without associated cells or proteins).
  • About 1% of bacterial species are capable of naturally taking up DNA under laboratory conditions; more may be able to take it up in their natural environments.
  • Only single-stranded DNA may pass through, one strand is therefore degraded by nucleases in the process, and the translocated single-stranded DNA may then be integrated into the bacterial chromosomes by a RecA-dependent process.
  • Illustration of bacterial transformation.

• Plasmids as Cloning Vectors

  • Plasmids can be used as cloning vectors, allowing the insertion of exogenous DNA into a bacterial target.
  • Plasmids may be conjugative/transmissible or non-conjugative.
  • Conjugative plasmids mediate DNA transfer through conjugation and therefore spread rapidly among the bacterial cells of a population.
  • Nonconjugative plasmids do not mediate DNA through conjugation.

• Agglutination Reactions

  • Agglutination reactions apply to particulate test antigens that have been conjugated to a carrier.
  • These conjugated particles are reacted with patient serum presumably containing antibodies.
  • Various methods of agglutination are used in diagnostic immunology and these incude latex agglutination, flocculation tests, direct bacterial agglutination, and hemagglutination.
  • Latex agglutination can also be performed with the antigen conjugated to the beads for testing the presence of antibodies in a serum specimen.
  • Direct bacterial agglutination uses whole pathogens as a source of antigen.

• Bacterial Transduction

  • Transduction does not require physical contact between the cell donating the DNA and the cell receiving the DNA (which occurs in conjugation), and it is DNAase resistant (transformation is susceptible to DNAase).
  • At the same time, some phage genes are left behind in the bacterial chromosome.
  • Generalized transduction is the process by which any bacterial gene may be transferred to another bacterium via a bacteriophage, and typically carries only bacterial DNA and no viral DNA.
  • In essence, this is the packaging of bacterial DNA into a viral envelope.
  • The new virus capsule, now loaded with part bacterial DNA, continues to infect another bacterial cell.

• Agrobacterium and Crown Gall Disease

  • A. tumefaciens can transfer part of its DNA to the host plant, through a plasmid - a bacterial DNA molecule that is independent of a chromosome.
  • Typically bacteria transfer plasmids through conjugation: a donor bacteria creates a tube called a pilus that penetrates the cell wall of the recipient bacteria and the plasmid DNA passes through the tube.
  • In the case of Crown Gall Disease, A. tumefaciens transfers a plasmid containing T-DNA into the cells of its host plant through conjugation, as it would with another bacteria.