Chemical warfare from an ecological perspective

Chemical weapons are recent acquisitions in humankind's ever-growing arsenal of destruction. But bacteria and fungi have been practicing chemical warfare for a very long time. Among the numerous and structurally diverse anti-microbial agents that microbes produce are penicillin by the mold Penicillium notatum, many important antibiotics by streptomycetes, a wide range of bacteriocins by Escherichia coli and most other bacteria (including the food preservative, nisin, by Lactococcus lactis), and killer toxins by the yeast Saccharomyces cerevisiae. In this issue of PNAS, Czaran, Hoekstra, and Pagie (1) perform numerical simulations to examine the effects of these interactions on microbial diversity. They come to the surprising conclusion that all this chemical warfare may actually promote biodiversity in the microbial realm. In essence, the authors show that high levels of diversity are maintained by the complex dynamics generated when a version of the “rock-scissors-paper” game (2, §) is played out in a spatial context.