Tetracycline resistance phenotype. BtetX (5 strains) or AtetX (1 strain) positive transformed C. reinhardtii, and CC-849 as a negative control, were grown in TAP media with (+C) and without antibiotic selection for 26 cell divisions. A 10 μL droplet containing 104 cells of each strain was plated on TAP plates supplemented with either 15, 25, 50 or 100 μg/mL of tetracycline and incubated with a light intensity of 25 μmoles m−2 s−1. The tetracycline resistance phenotype is present in all transformed strains. We expected confluent cell growth, however, there appears to be a selection for more resistant cells at higher tetracycline concentrations that grow as patches or along the periphery of the absorbed droplet. Negative controls did not grow at any assayed tetracycline concentration.