Microbes participate in various cooperative social behaviors, similar to macroorganisms, though the intimacy of their cooperative endeavors often exceeds those of larger organisms. Symbiosis among different microbial species evolved as a means to optimize the special skills that each species can contribute. Microbes cooperate to better exploit resources, resist stressful environments, protect themselves and their territory against other microbes, and to wage war.
Microbial populations battle each other, even those of the same species. Microbes use a myriad of antibiotics to defend their territory, or invade established communities.
There is considerable genetic diversity among individuals, even in communities of the same species. One study found that a bacterial population averaged only 72% similarity in genetic makeup.
The reason for this is the ease with which microbes can pick up and incorporate new genetic material via horizontal gene transfer. Individual microbes are highly genetically literate, though each in its own way.
Coexistence is maintained by cooperation. Above a certain threshold of genetic dissimilarity, antagonistic interactions increase sharply. Microbes are tribal.
Ishi Nobu, Spokes 2: The Web of Life (pre-publication)
Hélène Morlon, “Microbial cooperative warfare,” Science 337: 1184–1885 (7 September 2012).