Life has survived for more than three billion years because it is robust, and almost no mutations can easily outwit the defense mechanisms built up through eons of exposure to potential pathogens.
–Lawrence M. Krauss
Every second, every minute of your life, your body is under attack. This may be strange to think about, but millions of bacteria, as well as myriad other parasites, are attempting at this very moment to invade the sanctum of your body. Do not be offended, these creatures do not do this out of any sense of malice. They are simply driven by the two greatest necessities of life – survival and reproduction.
Ever since the first cells arose in the hot, steamy, soup that was our earth’s oceans billions of years ago, organisms have competed fiercely for the same limited resources. Some cells devised ways to halt the growth of or outright kill other cells, while others entered complex beneficial (mutualistic) or harmful (parasitic) interactions with each other. With time, two kinds of life forms emerged – parasites, who attack other organisms to their own benefit and the other’s loss, and hosts, who suffer from the parasites’ attack. A much larger class is that of pathogens – any organism that can directly cause disease in a host is called a pathogen. Host defense mechanisms have, therefore, evolved over eons to outsmart parasites and pathogens. Plants have specialized signaling systems to fight invading bacteria, and multicellular animals like human beings have an immune system with several tiers of defense to combat infection. Yet, at the same time, the parasites have been evolving too, devising sneakier and subtler ways of evading the host’s defense pathways to gain entry and live undetected. Life can, in fact, be described as a continuous arms race between hosts and their parasites, where neither gains the upper hand on the other, even after centuries of creating sophisticated arsenals for the purpose.
This continuous struggle has given rise to some truly ingenious forms of biological innovation. A recent study from Xuezhi Zhang and colleagues, working in a collaboration between the University of Geneva, Switzerland, and Baylor College of Medicine, USA, sheds light on a remarkable and evolutionarily ancient line of defense employed by a class of social amoeba. Simply put, the defense consists of casting a net formed of DNA molecules over bacteria and killing them slowly with poisons embedded in the net.