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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)


“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,” 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 the Uni­vers­ity of Ca­li­for­nia 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.” The tox­in is in­jected into the vic­tim, the re­search­ers said, and may kill it or stop it from grow­ing.

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 trop­ical 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 others 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 getting 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 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.”


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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.”