Editing Digestion (section)

====Conjugation machinery====
The [[Bacterial conjugation|conjugation]] machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in ''Agrobacterium tumefaciens'', which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor).<ref name=Cascales>{{cite journal |vauthors=Cascales E, Christie PJ |title=The versatile Type IV secretion systems |journal=Nature Reviews Microbiology |volume=1 |issue=2 |pages=137–149 |year=2003 |doi=10.1038/nrmicro753 |pmid=15035043|pmc=3873781 }}</ref> The VirB complex of ''Agrobacterium tumefaciens'' is the prototypic system.<ref name=Christie>{{cite journal |author1=Christie PJ |author2=Atmakuri K |author3=Jabubowski S |author4=Krishnamoorthy V |author5=Cascales E. |title=Biogenesis, architecture, and function of bacterial Type IV secretion systems |journal=Annu Rev Microbiol |volume=59 |pages=451–485 |year=2005 |issue=1 |doi=10.1146/annurev.micro.58.030603.123630 |pmid=16153176|pmc=3872966 }}</ref>

In the [[Diazotroph|nitrogen-fixing]] ''[[Rhizobia]]'', conjugative elements naturally engage in inter-[[Kingdom (biology)|kingdom]] conjugation. Such elements as the ''[[Agrobacterium]]'' Ti or Ri plasmids contain elements that can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of [[opines]], which the bacteria use as carbon and energy sources. Infected plant cells form [[Agrobacterium tumefaciens|crown gall]] or [[Agrobacterium rhizogenes|root tumors]]. The Ti and Ri plasmids are thus [[endosymbiont]]s of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.

The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the ''tra'', or transfer, operon) from that for inter-kingdom transfer (the ''vir'', or [[virulence]], operon). Such transfer creates virulent strains from previously avirulent ''Agrobacteria''.