Competition among bacteria is widely known to occur among individual members of single colonies, or betweem closely related strains. However, bacterial rivalry is not limited to that. Recently we have found that Paenibacillus dendritiformis (T morphotype) secretes inhibiting agents that are lethal above a threshold. When two neighboring sibling colonies (colonies initiated from the same bacterial culture) grew from droplet inoculation, all the bacteria at the interface of the inhibited regions died. Although P. dendritiformis are able to produce spores, death rather than sporulation occurred under these conditions. Although the extent of inhibition is greater for lower initial nutrients levels, it persists even for relatively high nutrient levels, which excludes bacterial cannibalism (killing due to lack of nutrients).
Analysis of the material (proteins) secreted by competing sibling P. dendritiformis colonies show that they include subtilisin, which stimulates cell growth and reproduction, and a lethal protein termed Slf (sibling lethal factor). Our results, combined with a mathematical model, show how colonies maintain their growth by self-regulating the secretion of subtilisin and Slf.
 Be’er, A., H.P. Zhang, E.-L. Florin, S.M. Payne, E. Ben-Jacob, and H.L Swinney, 2009, Deadly competition between sibling bacterial colonies, Proceedings of the National Academy of Sciences , 106 (2): 428-433.