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Electroporation of PCC6803

This experiment can be used to introduce autonomously replicating plasmids to PCC6803.

Methods

50 mL linear phase Synechocystis at OD₇₃₀ 0.5 collected by centrifugation
wash cells three times with 1mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer pH 7.5
remove supernatant, resuspend in 100 uL of the remaining liquid by vortexing
60 uL of cell suspension mixed with 0.1-16 ug DNA (dissolved in H₂O) and electroporated with Biorad gene pulser (25uF capacitor used, time constant varied buy changing resistors (100, 200, 400, & 600 OHMS for time constant 2.5, 4.8, 9, 13 ms, respectively, electric field varied from 0-12kV cm-1)
IMMEDIATELY after electric pulse, cells resuspended in 1 mL BG11 & mixed with 50 mL BG11 in an Erlenmeyer flask
cells incubated 5 days under **specified growth conditions
50 mL culture collected by centrifugation, resuspended in 500uL of remaining liquid, mixed with 5mL BG11 soft agar (BG11 + 0.75% agar)
Pour on plates with 25 mL BG11 agar with antibiotic
determine number of viable cells after electroporation: 10^-4 dilution made before collecting the culture, 50 uL of this dilution plated with out selection, incubate 14 days, count colonies. Total viable cells (colonies grown on non-selective plates * 10^7) and total number transformants (colonies on selective plates) determined

- cultivation: Synechocystis is photoautotrophically grown in BG11, for BG11 agar plates, BG11 supplemented with 10mM N-Tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid (pH 8), 12mM Na₂S₂O₃, & 1.5% Agar

40uL of cells at 10^9 cells/mL were mixed with 5 uL of plasmid DNA solution (1ug/uL). Electroporation was performed at field strength of 12kV/cm at a constant of 5ms, with no cell death detected. (Mermet-Bouvier)*used for PCC6803 and other strains.
This protocol is adapted from a protocol for PCC6714, which is not naturally competent. However it seems we can use this for PCC6803 so we can obtain autonomously replicating plasmids.
Ludwig, Alfred, “Transformation and gene replacement in the facultatively chemoheterotrophic, unicellular cyanobacterium Synechocystis sp. PCC6714 by electroporation,” Appl Microbiol Biotechnol (2008) 78:729–735

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