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Images: Bacteria Exhibit Altruistic Behavior

Microbiologist Tracy Mincer of WHOI is working to discover compounds made by marine microbes that could have applications in human medicine. In a study recently published in the journal Science, he and his colleagues identified and partially characterized several potent antibiotics. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)
A test plate shows the killing effect of some strains of Vibrio bacteria on another strain. The nutrient gel in this dish was evenly covered with a yellowish "target" strain. Then small spots of other bacterial strains were placed at random on top. "Halos" indicate where added strains killed the target bacteria. The size of a halo is related to the number of cells that died. The arrow indicates a spot of added bacteria that lacks a halo; the strain in this spot did not kill the target strain. (Photo courtesy of Hans Wildschutte)
Microbial ecologist Martin Polz (left) and theoretical biologist Otto Cordero of MIT led a team investigating the interactions among 185 strains of the marine microbe Vibrio. They found that many of the strains produce antibiotics that don't kill strains that are closely related to themselves, but do kill other strains that are not closely related to them. (Photo by James Long, Massachusetts Institute of Technology)
Researchers created this diagram to summarize their findings about lethal interactions among 185 strains of Vibrio bacteria. Individual strains of bacteria are represented by the black lines protruding from the rim of the circle. Those adjacent to each other on the rim are more closely related than those farther apart. The black lines radiate from a Vibrio family tree (displayed in circular form rather than the more common vertical "tree" arrangement).  Each green line represents an interaction between two strains in which one of the strains produces an antibiotic that kills the other. Blue bars along the circumference indicate strains that are killed by at least one other strain. Black bars indicate strains that kill at least one other strain. Red bars indicate "super killers"—strains that kill at least ten other strains. (Otto Cordero, Massachusetts Institute of Technology)
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