BACTERIA MAKE LETHAL PROTEINS TO KILL OTHER ORGANISMS
Before discussing human biological combat, let’s remember that biological warfare has been practiced throughout evolutionary history by organisms at all levels on theevolutionary scale. Many of the following examples have already been discussed under different headings; here, we will summarize them briefly before talking about deliberate use of biological agents in human conflict.
When related bacteria compete for the same habitat or same resources, they often kill each other, using toxic proteins known as bacteriocins . Generally speaking, bacteria are most likely to kill their close relatives because the more closely related two strains of bacteria are, the more likely they will compete for the same resources. For example, many strains of Escherichia coli deploy a wide variety of bacteriocins, referred to as colicins , intended to kill other strains of the same species. The genes for colicins are normally carried on plasmids. The colicin plasmids of E. coli have been used as the basis of many plasmids commonly used in molecular biology and genetic engineering . Yersinia pestis , the plague bacterium, also makes bacteriocins, called pesticins in this case, designed to kill competing strains of its own species.
When proteins produced by bacteria act against higher organisms we refer to them as toxins . The difference in terminology between bacteriocin and toxin is thus really a matter of perspective. Bacteria deploy bacteriocins against their fellow bacteria with the deliberate intention of killing them. In contrast, pathogenic bacteria do not usually “intend” to kill the people they infect. The longer the host organism stays alive, the longer it provides a home for the infecting bacteria. Bacteria also infect insects and make toxins that kill insects but are harmless to vertebrates. The bacterium Bacillus thuringiensishas become famous for its production of a toxin that kills insect pests.