A possible role for plasmids in mediating the cell-cell proximity required for gene flux

One of the major requirements for successful gene flux is a close proximity between participating organisms. In previous articles, we have proposed that plasmids act as powerful vehicles transporting genes collected by integration and transposition, mainly via the process of conjugation. However, in addition to conjugation, there are other processes, also mediated by plasmids, in which different cells come into very close contact with each other, such as symbiosis and the formation of multi-specific cellular communities. There is evidence that suggests that such intimate associations between cells may facilitate gene transfer events, even between distantly related organisms. Examples of symbiotic endosymbiotic, and parasitic associations provide evidence in support of the role of plasmids in bridging the genetic gap between species. In this purely theoretical article we attempt to conceptualize existing data on this subject, provide new insights and present testable predictions on how plasmids may facilitate gene flux by bringing cells together. (C) 1996 Academic Press Limited.