形質導入

Transduction is a virus-mediated process that transfers genes between bacteria through bacteriophages, or bacterial viruses. Unlike transformation and conjugation, which require direct DNA uptake or cell-to-cell contact, transduction relies entirely on phage infection. This mechanism can transfer antibiotic resistance genes, toxins, and virulence factors, making it a major driver of bacterial evolution and adaptation.

During the lytic cycle, bacteriophages infect bacterial cells, replicate within them, and cause cell lysis. Occasionally, random fragments of the bacterial genome are mistakenly packaged into viral capsids instead of viral DNA. When these defective phage particles infect new hosts, they introduce mispackaged bacterial DNA. If this DNA recombines with the recipient's genome, it may confer new traits, though the process is non-specific since any bacterial chromosome segment can be transferred.

Specialized transduction occurs when temperate phages like Lambda incorrectly excise from the bacterial chromosome during the lysogenic cycle. Improper excision incorporates adjacent bacterial genes into the phage genome. Unlike generalized transduction, specialized transduction transfers only specific genes located near the prophage integration site, such as the gal genes near the att site in E. coli, making it a selective process.

Transduction plays a significant role in disseminating antibiotic resistance genes among bacterial populations. Bacteriophages can package and transfer resistance genes to new hosts, allowing bacteria to develop resistance mechanisms against antimicrobial agents. This process accelerates the development of antibiotic resistance and contributes to the emergence of resistant bacterial strains in clinical and environmental settings.

Virulence factors, such as toxin-producing genes, can be disseminated between bacteria through transduction. When bacteriophages transfer these genes to new hosts, they enhance the pathogenicity of recipient bacterial strains. This horizontal transfer of virulence determinants allows bacteria to acquire disease-causing capabilities, increasing their ability to cause infection and evade host immune responses.

The Lambda phage integrates its DNA at specific attachment (att) sites in the bacterial chromosome, such as between the gal and bio operons in E. coli. During induction, improper excision from these integration sites can incorporate nearby bacterial genes into the phage genome. This location-dependent mechanism explains why specialized transduction transfers only genes adjacent to the att site, unlike the random transfer in generalized transduction.

Transduction facilitates genetic exchange independent of direct cell-to-cell contact, allowing bacteria to rapidly acquire new traits and adapt to diverse environments. By enabling the transfer of antibiotic resistance genes and virulence factors, transduction promotes bacterial survival in hostile conditions imposed by antibiotics and host immune responses. This mechanism accelerates bacterial evolution and enhances population-level adaptation.