How do transformed bacteria demonstrate successful uptake of plasmids?

Transformed bacteria demonstrate successful uptake of plasmids primarily by producing proteins encoded by the plasmid. When bacteria take up a plasmid through a process called transformation, they often acquire new genes that the plasmid carries. These genes can code for proteins that the bacteria did not previously produce. For instance, if the plasmid contains a gene for antibiotic resistance, the bacteria will start synthesizing the protein that confers this resistance, ultimately allowing them to survive in environments where they would otherwise be killed by the antibiotic.

The presence of the new proteins can be confirmed through various techniques such as Western blotting or functional assays, confirming that the transformation has been successful. Other options, such as growing in an antibiotic-free environment, do not specifically indicate that plasmid uptake has occurred, as those conditions alone would not show whether the bacteria have expressed any new traits. Changing color could be an indirect indication in specific experiments (like using colorimetric assays), but it isn't a general marker of plasmid uptake. A reduction in growth rate does not signify successful transformation and could actually be indicative of other issues affecting bacterial health rather than showcasing successful genetic uptake.