E. Coli Can Mutate Nearby Bacteria

Some bacteria can trigger unexploded viral grenades in neighboring bacteria’s DNA. Certain Escherichia coli bacteria, including some that live in human intestines, make a chemical called colibactin. That chemical awakens dormant viruses inside nearby bacteria, sometimes leading to their destruction. This type of biological warfare among bacteria hasn’t been described before.

Colibactin producers must creep up on their bacterial enemies and trigger the unexploded ordinance hiding in the enemies’ DNA. Those grenades are prophages — bacteria-infecting viruses that have inserted themselves into their hosts’ DNA, where they hide out harmless and dormant until something triggers their awakening. That something, in this case, is DNA damage caused by colibactin. When colibactin dings DNA, a bacterial repair system called the SOS response kicks in. What many phages have done is to tap into that response. It’s a signal for them to move out of this dormant lifestyle and awaken to kill their host and move on to find a new host. Once phages wake up, they replicate and burst out of the host cell, destroying it. But once these viral grenades go off, they can infect other bacteria, potentially exposing the attacking bacteria and other close-by microbes to biological shrapnel.

Humans might also get caught in the cross fire. Researchers already knew that colibactin can cause damage to human DNA that may lead to colon cancer. But why the bacteria would use the chemical against people wasn’t known. The new research suggests that E. coli may not be producing colibactin to assault its human hosts, but as a countermeasure against other microbes. Among bacteria, colibactin isn’t usually a lethal weapon. In most bacteria examined, colibactin caused DNA damage, but the bacteria were able to repair the wounds. That may be because colibactin is an unstable chemical that quickly degrades before it can break enough DNA to do irreparable harm. Some bacteria also make other chemicals that defuse colibactin before it can damage DNA. Only bacteria that have unexploded prophages in their DNA and no other defenses were vulnerable to colibactin-producing bacteria in laboratory dishes.

CITATIONS J.E. Silpe, et al. The bacterial toxin colibactin triggers prophage induction. Nature. Published online February 23, 2022. doi: 10.1038/s41586-022-04444-3.