Conjugation: Transfer of Chromosomal DNA by HFr Strains

Last updated on June 14th, 2021

The F+ strain which contains the plasmid gene as an episome (i.e.  F plasmid becomes integrated into the host cell genome at one of the several possible sites of a chromosomal gene) induces more than a thousand times the number of genetic recombination than seen in F+ and F- cells.  

Such a donor strain is called a high frequency of recombination (HFr) strain.

HFR Cell: F plasmid integrated in to Bacterial chromosome
HFR Cell: F plasmid integrated in to Bacterial chromosome
  1. The HFr strain is able to transfer some of the host genes to the recipient.
  2. The sex pilus contacts the recipient F- cell and pulls the cells together
  3. The donor chromosome is transferred as SS DNA starting at the origin of transfer. Gene that is closest to the origin is transferred first.
  4. Segments of the integrated plasmid are at the beginning and the end of the DNA being transferred (Note: Yellow part is integrated plasmid.Bacterial gene transfered by HFR
  5. To transfer the entire plasmid, the entire bacterial gene must be transferred first. But the donor and recipient cells separate  prior to the complete transfer of genome  and plasmid
  6. Usually, only part of the F plasmid called the initiating segment is transferred along with adjacent chromosomal genes.
  7. Transferred DNA becomes double-stranded
  8. The donor DNA is integrated into the recipient cell’s DNA by homologous recombination.
  9. The recipient now carries transferred genes but remains F- whereas the donor cell remains HFr.Final outcome of HFR Conjugation
  10. The recipient cell does not become an F+ donor cell, as only a part of the F plasmid is transferred but the donor cells remain as Hfr strains.
About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.