Bacteria have plenty of ways to combat the viruses that plague them, called phages. The CRISPR-Cas system and restriction enzymes that cleave phage DNA are the best understood, but there are others. They use a variety of different mechanisms and stop phages at various stages of infection, but they all rely on biological actors: proteins and RNA. New work has just revealed, though, that bacteria can use chemical weapons as well.
Bacteria produce a wide range of active small molecules that are not essential for survival but do confer a growth advantage. Some of these small molecules, which kill their fellow microbes, are already used (by us) as antibiotics. It was also observed, more than fifty years ago, that bacteria make molecules that can inhibit the growth of phages. But it wasn’t clear whether these molecules are made specifically because they slow down the phages. Only now, with the background knowledge that (a) bacteria make a lot of bioactive compounds, many of which do combat other microorganisms, and that (b) phages are a major scourge for bacteria, did researchers think to check.
Biochemists screened 4,960 compounds for their ability to protect E. coli from phage infection and found 11 that could. Nine out of the 11 were what are termed DNA-intercalating agents. The nucleotides that comprise DNA (A,T, C, and G) are flat molecules, and they’re stacked parallel to each other along the DNA helix. DNA-intercalating agents slide in between them, interfering with the copying of DNA during cell division.