[83] Conjugal transfer of DNA to cyanobacteria

This chapter focuses on the conjugal transfer of DNA to Cyanobacteria. Conjugation appears to be a general means to introduce DNA from Escherichia coli into cyanobacteria, using the broad host range conjugal apparatus of an IncP plasmid, such as RP4. RP4, originally isolated from Pseudomonas, has been shown to mediate the transfer of DNA into a wide range of gram-negative bacteria, including such distantly related organisms as myxobacteria, thiobacilli, and unicellular and filamentous cyanobacteria. To obtain stable conjugal transfer it is necessary that (1) conjugal contact be made, (2) transferred DNA escape restriction or degradation, and (3) the DNA replicate autonomously or integrate into one of the replicons of the recipient. The first requirement is probably met in the great majority of gram-negative eubacteria, cyanobacteria included. The task for the experimenter is to find conditions that permit the last two requirements to be met as well. Even with transformable unicellular cyanobacteria, conjugation may be the preferred route of DNA transfer in certain cases. DNA taken up by unicellular cyanobacteria appears to be randomly cut early during the transformation process, so that the efficiency of transfer of a segment of nonhomologous DNA decreases exponentially with its length.