Among the three main modes of HGT—transformation, conjugation, and transduction—transduction is unique in that it is mediated by bacteriophages, or bacterial viruses.
Transduction occurs in two ways. Generalized transduction occurs during the lytic cycle of a bacteriophage infection. In this process, bacteriophages infect bacterial cells, replicate within them, and ultimately cause cell lysis, releasing newly assembled virions. Occasionally, random fragments of the bacterial genome are mistakenly incorporated into the viral capsid instead of viral DNA. When these defective phage particles infect a new bacterial host, they introduce mispackaged bacterial DNA rather than viral genetic material. If the introduced DNA recombines with the recipient bacterium’s genome, it may confer new traits to the host. Since the transferred genetic material is randomly selected, generalized transduction is a non-specific process that can move any segment of the bacterial chromosome.
Unlike generalized transduction, specialized transduction occurs due to errors during the lysogenic cycle of a temperate bacteriophage. Temperate phages, such as the Lambda phage in Escherichia coli, integrate their DNA into the bacterial chromosome at specific attachment (att) sites. This integrated prophage remains dormant until induction, at which point it excises itself to enter the lytic cycle. However, improper excision can result in the incorporation of adjacent bacterial genes into the phage genome. These genes, now part of the viral genome, are subsequently packaged into new phage particles and transferred to other bacterial cells upon infection. Unlike generalized transduction, specialized transduction is limited to bacterial genes located near the prophage integration site, leading to the selective transfer of specific genetic elements.
Transduction is a major driver of bacterial evolution and adaptation. It plays a significant role in the spread of antibiotic resistance genes, allowing bacteria to develop resistance mechanisms against antimicrobial agents. Additionally, virulence factors, such as toxin-producing genes, can be disseminated through transduction, enhancing the pathogenicity of bacterial strains. By facilitating the exchange of genetic material independent of direct cell-to-cell contact, transduction provides bacteria with an evolutionary advantage, promoting adaptation to diverse environments, including hostile conditions imposed by antibiotics and host immune responses.
In addition to transformation and conjugation, horizontal gene transfer also occurs through transduction.
It is a virus-mediated process that facilitates the transfer of genes between bacteria, including those for antibiotic resistance, toxins, or virulence factors.
Transduction occurs in two ways. In generalized transduction, random fragments from bacterial DNA are mistakenly packaged into new phage particles during the lytic cycle.
When this phage infects a new host, it injects the mispackaged bacterial DNA into the host cell.
In specialized transduction, excision errors during induction result in the inclusion of nearby bacterial genes.
For example, during the lysogenic cycle of the lambda phage, its DNA integrates at the Att site between the gal and bio operons in E. coli.
During induction, it may excise incorrectly, carrying adjacent gal genes.
The resulting phage particle carries specific bacterial genes, which can then be transferred to another bacterium.
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