It is a sex factor which is present in protoplasm of bacteria that get transferred during the conjugation . This colicin factor is respsnsible for production of certain protein or polypeptide antibiotic called colicin or bacteriocin .This factor was first observed in E.coli. This factor kills the bacteria which posses closely related strains or species.
Sunday, October 2, 2011
b) Resistance factor or R-factor.(RF)
The R- factor are extra extra chromosomal genes which carry information of resistance against variety of antibiotics. It gets transferred to the receipient along with sex factor. These genes get transferred rapidly to the antibiotic sensitive cells by conjugation. These genes get transferred between bacteria like E.coli ,Salmonella typhi and Shigella dysentriae. It has been observed to increase resistance against four iwdesly used antibiotics like sulphanilamide, streptomycin, chloramphenicol and tetracycline.
Conjugation by Sexduction
It is the process of transferring genetic material from donor to recipient by a sex factor. In this method , from the endogenote of HFr the F factor or sex factor disintegrate resulting the reversion of HFr to F+ state but this F+ factor along with small part of endogenote is called F factor and the cell is called F’ cell. When conjugation between F’ cell and F- cell takes place ,the cell with some transferred genes takes place. In this way transfer of genes takes place.
Conjugation by episome
The episome are the bacterial cell whose fertility factor integrate with endogenote and then replicate followed by migration of the combined endogenote ,. This cell with combined endogenote is called HFr( high frequency recombination) . When HFr and F-comes together and recombination can take place,then HFr is called fertile male .During conjugation HFr duplicate and then one of loop break at the junction of endogenote and fertility factor. The broken part with endogenote part move through conjugation tube .In this way transfer of genetic character takes place.
Conjugation by F particle
The F+ and F- bacteria first come in closer. The F+ cell produce filamentous structure called sex-pilus from cell wall which attach the cell wall of F-to form conjugation tube .The F- particle of F+ then duplicate and then replicate to form two strands . One remain in F+ cell and another passes through the conjugation tube and remain in F- as an independent F- particle . Now the F-changes to F+
Sexual Reproduction in bacteria by Conjugation and sex factors
Conjugation is a sexual type of reproduction in bacteria in which there is transfer of genes between two bacteria by directly coming in contact with each other. The conjugation was first described by Lederberg and Tatum(1946) in E.coli and other species of Gram –negative bacteria . Till now it hasn’t been found to be discovered in Gram –positive bacteria.
In the conjugation process the bacteria which donate genes or DNA is called donor cell or male cell and the other which receive the genes or DNA is called receipient cell or female cell. Each male cell posses an additional double stranded circular piece of small DNAin cytoplasm which is called a plasmid or sex factor . The sex factor is 1/1000 th size of enogenote( normal bacterial chromosome). Till now according to Lederberg and Tatum three types of sex factors are known. They are named as
a) Fertility factor or F factor (FF)
b) Resistance factor or R-factor.(RF)
c) Colicin factor or Col-factor(CF)
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