Last year's Schol Bio paper had a question about allelopathy. The context centred on Black Walnuts (Juglans nigra). These are large deciduous trees with an extensive root system - and they release an allelopathic chemical called juglone, which has a number of toxic effects on a range of other plant species. This ability to kill or weaken potential competitors is a significant advantage to J.nigra as it improves the survival of walnut seedlings, and reduces competition for resources such as water, light, and nutrients.
Such allelopathic chemicals are relatively widespread in nature, although we may give them different names depending on the organism producing them. For example, the chemicals produced by fungi to inhibit bacterial growth are called antibiotics (some of which are the basis of many modern antibiotic treatments for infection - 'penicillin' was just the first of these). Similarly some bacteria produce substances that kill off fungi. The term 'antibiotic' was first coined to describe streptomycin, originally isolated from an organism called Streptomyces. (As an example of how science moves along: Streptomyces belongs to a group of microbes called actinomycetes. The suffix -myces suggests they are fungi, & in fact that's how they were described when I first encountered them. However, they're now classified as prokaryotes, along with other bacteria.)
For a long time we've regarded these allelopathic chemicals as a form of biological warfare, produced by one species to kill off or deter competitors. So I was intrigued to read an article (Mlot, 2009) that suggested that they could have other, quite different functions in the microbial world.