How Does Bacteria Kill Their Competitors?

Bacteria kill their competitors by using antibiotics, toxic proteins that can kill other microorganisms.  These microorganisms can be of the same or different species. Bacteria known as Bacillus subtilis produce proteins that kill sister cells.  This behavior occurs when the bacteria are grown on a medium void of nutrients.  Sporulating cells release toxic proteins into the surrounding environment, lysing non-sporutlating cells of the species.  The lysed cells release nutrients that the sporulating cell can then use.  Once the sporulating cell uses these nutrients, spore formation stops and the cell grows.  This cannibalism is important for the bacterial species because it allows the bacteria to have a small population of sporulating cells and a larger number of growing bacterial cells. (González-Pastor, 2011)Streptococcus pneuomoniae is an example of bacteria that produces an antimicrobial that kills other microorganisms.  The reason this bacteria may kill other microorganisms is to transform itself, producing genetic diversity.(González-Pastor, 2011).  While some bacteria secrete the antimicrobial into its surrounding environment, others directlyinject toxic proteins into other bacteria using a special “needle complex”.  This is seen in Pseudomonas aeruginosa, Shigella flexneri, Salmonella enterica, and Yersinia enterocolitica.(Hauser, 2009)A similar phenomenon is seen inVibrio cholera, the bacteria that cause cholera.  The bacteria produces a projection that is injected into other cells, toxins are secreted from V. cholera into its competition causing the competitor cell to lyse.  The DNA from the competitor is then absorbed into the V. cholera, transforming it. This enables the bacteria to become resistant to drugs, if the bacteria incorporates a drug resistant gene. (Yong, 2015).  The bacteria are killing competitors to survive: acquire nutrients and evolve.



González-Pastor, J. E. (2011). Cannibalism: a social behavior in sporulating Bacillus subtilis. FEMS Microbiology Reviews, 35 (3), 415–424.

Hauser, A. R. (2009). The type III secretion system of Pseudomonas aeruginosa: infection by injection. Nature Reviews Microbiology (7), 654-665.

Yong, E. (2015, January 1). Cholera Bacteria Kill Each Other With Spears to Steal DNA. Retrieved from