Effective transformation of the cyanobacterium Spirulina platensis using electroporation

Although Spirulina (Arthrospira) is expected to be a suitable organism for producing recombinant proteins, a gene transfer system has not yet been established, due to a lack of suitable vectors and because Spirulina appears refractory to common genetic manipulations. As the initial stages of the development of recombinant DNA methodology, we examined the effects on transformation efficiency of electroporation conditions such as electric-field strength (2, 4, 6, 8, 10, 12 kV cm^-1) and time constant (2.5, 5 ms). At a time constant of 2.5 ms, few transformants were observed regardless of the field strength. The longer time constant of 5.0 ms reproducibly yielded transformants at the middle field strength of 4 - 8 kV cm^-1, but gave high killing and no transformation at the higher field strength of 10 - 12 kV cm^-1. Chloramphenicol acetyltransferase (CAT) activities were increased only in the transformants from 2-6 kV cm^-1 and 5.0 ms. The density of the transformants was significantly correlated with the relative value of CAT activity (r = 0.89, n = 11, p < 0.01), suggesting that the chloramphenicol resistance was due to CAT activity. We concluded that transformation of S. platensis was most effective at a pulse duration 5.0 ms with an electric field of 4 kV cm^-1, and that foreign genes can be expressed in this organism.