Organisms used for DNA transformation experiments were tested for sensitivity to five antibiotics in two different concentrations. Cell culture growing in F2 media with 3% seawater was divided to fifteen 15ml tubes, i.e. three tubes for testing each of the antibiotics: antibiotic was added to two samples to the final concentrations noted in Table 1, the third tube in the set served as a control. The cultures were incubated under 12h light cycle and 20°C and checked by light microscophy 1, 4, 7 and 19 days after the addition of antibiotics. ABCDEF1antibiotic puromycin blasticidin geneticin hygromycin zeocin 2concentration 1 5 μg/ml 5 μg/ml 200 μg/ml 200 μg/ml 100 μg/ml 3concentration 2 10 μg/ml 10 μg/ml 400 μg/ml 400 μg/ml 200 μg/ml Table 1: Tested antibiotics and concentrations