Optimal condition for efficient DNA transfer in filamentous cyanobacteria by electroporation

Filamentous cyanobacteria are an ecologically important group of bacteria because they are able to provide both organic carbon and fixed nitrogen that can support the nutritional requirements for other microorganisms. Because of their prokaryotic nature, they can also be used as potentially powerful model systems for the analysis of oxygenic photosynthesis and nitrogen fixation. Gene transfer is an indispensable procedure for genetic analysis of filamentous cyanobacteria. Electroporation was used to introduce foreign DNA into cyanobacterial cells. In experiments designed to optimize the electroporation technique, the effects of the field strength (amplitude of pulse) and time constant (duration of pulse), DNA concentration and host restriction/modification of DNA on the efficiency of electro-transformation were investigated. The results of this research revealed that a high voltage pulse of short duration was effective for the electro-transformation of Anabaena sp. M131. The maximal number of transformants was obtained at 6 kV/cm with a pulse duration of 5 msec. The efficiency of electro-transformation was also sensitive to concentration of DNA; even small amounts of DNA (0.01 mu g/ml) were able to give a large number of transformants (1.0 x 10(3) cfu/ml).