Final answer:
Plasmids in bacteria can encode toxic proteins called colicins that can kill other bacterial strains. These toxic proteins are not usually transmissible to other cells. Plasmids can be transferred between bacteria, facilitating the spread of the toxic proteins.
Step-by-step explanation:
In bacteria, plasmids can encode one or more proteins that are toxic to other bacterial strains. These toxic proteins, known as colicins, can kill other bacteria when in close proximity. However, they are not usually transmissible to other cells. Plasmids are small circular pieces of DNA that can be transferred between bacteria, allowing for the spread of these toxic proteins.