My repeat biofilm experiment was seriously compromised by a tube-label failure - the identifying numbers I'd written on the culture tubes mostly washed off when I washed the crystal violet stain from the tubes. (Somehow my new red sharpie's writing didn't stick to the surface of the new glass tubes, but instead flaked off like a whiteboard marker.)
Luckily I'd also labeled each tube to indicate the treatment, and these marks (other sharpies) didn't wash off. The blue bars are the amount of crystal violet that stained tubes that had been pretreated with DNA. The green bars are for tubes pretreated with just the buffer, and the pink bars are for tubes pretreated with buffer and then given 1 µg DNA/ml in solution in the cell culture.
If we set aside the murR749 hypercompetent mutant, I can make a few (weak) generalizations. First, my DNA pretreatment didn't increase the amount of staining, and thus didn't increase the numbers of cells adhering to the sides of the tubes. Second, adding dissolved DNA to the cultures may have slightly increased the amount of staining. Third, the use of the sxy hypercompetent mutant or either non-competent mutant (sxy- or pilA-) didn't affect the amount of staining.
The murE749 mutant had higher staining than the other strains, especially if I ruthlessly assign the high 'unknown' to it. This strain's staining was also higher in the first version of this experiment.
Is any of this worth following up on? I don't think I'll bother to repeat this experiment using a more reliable Sharpie. Should I put more effort into getting DNA attached to a surface? I think first I should finish my post about what biofilms are...
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