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Microbes attack each other with “poison-tipped swords”

Nov. 17, 2010
Courtesy of the UNC School of Medicine
and World Science staff

Bat­tles among bac­te­ria are more com­plex than once im­ag­ined, and in­clude the use of “poi­son-tipped swords” that can al­so be stol­en from dead en­e­mies, sci­en­tists say based on new re­search.

The find­ings from this mi­cro­scop­ic war zone may be use­ful for hu­mans, who could ex­ploit the mi­cro­bi­al com­bat tech­niques to de­stroy un­wanted germs, the in­ves­ti­ga­tors add.

Dif­fer­ent strains Esch­e­rich­i­ coli</i>, which re­search­ers say is the first bac­te­ri­al spe­cies found to de­ploy "contact-dependent tox­in de­liv­ery systems," shown above in ar­ti­fi­cial col­or. (Cour­te­sy UNC)

Battles among bacteria are more complex than once imagined, and include the use of “poison-tipped swords” that can also be stolen from dead enemies, scientists say based on new research. The findings from this microscopic war zone may be useful for humans, who could exploit the microbial combat techniques to destroy unwanted germs, the investigators add. “It has been known for a long time that bacteria can produce toxins that they release into their surroundings that can kill other bacteria, sort of like throwing hand grenades at enemies,” said Peggy A. Cotter, a microbiologist at the University of North Carolina at Chapel Hill. “Our data suggests that the situation is far more complex that we thought,” she added: in David A. Low’s lab at U.C. Santa Barbara, it was also found that bacteria can produce molecules on their surface that harm or kill other bacteria upon contact. “It appears that some bacteria participate in ‘man to man,’ or ‘bacteria to bacteria’ combat using poison-tipped swords,” Cotter said. “What we have discovered is that each bacterium can have a different poison at the tip of their sword.” For each poison, there’s a specific protective protein molecule “that the bacteria also make so that they don’t kill themselves and are not killed by other members of their same ‘family,’” she explained. The research by Cotter, Low and others appears online Nov. 18 in the the research journal Nature. The “sword” image isn’t that far off, the researchers note. The killer proteins are large and rod-shaped in a range of bacteria including the disease-causers Bordetella pertussis, the cause of whooping cough and Burkholderia pseudomallei, and a cause of often fatal tropic disease. “In the soil or in humans, different bacteria bump into each other all the time and bump into their own ‘family,’ too. They have to touch each other and recognize each other and then one can inhibit the growth of the other, non-family, bacteria.” Cotter said. This system may represent a primitive form “kin selection,” she added, whereby organisms slay organisms that are genetically different but not those that are closely related. “As an additional twist, we have found that some bacteria can have two or three or possibly more systems. Our data suggest that these bacteria will be protected from killing by bacteria that produce any of three types of poison swords and they will be able to kill other bacteria that lack at least one of those types of immunity proteins.” These bacteria may acquire these additional systems by acquiring genes from other bacteria, she added. “It seems that they may be able to kill their enemy and then steal the poison-tipped sword and protective (immunity) protein from the dead enemy, increasing their own repertoire of weapons.” By teasing out the genetics of these bacterial close combat mysteries, it may someday be possible to “engineer an organism, a non-pathogenic variant, and by putting it out in the environment, such as soil, you can potentially get rid of other pathogens,” Cotter said. “Or you could decontaminate an area, if the new knowledge is applied to biodefense.”