Asked by: Karl Lewis, Malta
Yes. These viruses are called bacteriophages and they are extremely common. Around a quarter of the bacteria in the sea at any one time are infected by bacteriophages and they are so successful that the viruses often outnumber bacteria by a factor of 10. Bacteriophages have a strand or loop of DNA enclosed in a special protein sheath that acts like a hypodermic syringe. One end binds to proteins on the bacterial cell membrane and this causes the sheath to contract, puncturing the membrane and injecting the DNA. The virus’s genes are then automatically transcribed by the bacterium’s own cellular machinery, which builds hundreds of copies of the virus. After about 20 minutes the bacterium is so full of new viruses that it bursts open, releasing the viruses to infect other cells.