Bacillus subtilis is a gram positive bacterium that plays a fundamental role in shaping the soil ecosystem. As such it is exposed to unavoidable interactions with bacterial species living in its surroundings. We chose to study the interactions between two robust biofilm formers- Bacillus subtilis and closely related Bacillus firmus. Both bacterial species reside in and compete for the same ecological niche - the soil. Dramatically, the proximity between the colonies resulted in B. subtilis enclosing the B. firmus biofilm in a well-designed ring. This engulfment coupled with the secretion of various killing molecules lead to the death of the B. firmus cells in its biofilm. Using bacterial genetics and comparative Mass-Spectrometry we found that the molecules responsible for the killing of B. firmus are a lipoprotein, a short peptide and a protein, so far considered to be self-regulators of the B. subtilis social behaviors. Additionally, exposure to the identified killing molecules during the antagonistic interaction promoted rapid evolution of the bacterial species involved. This work suggests new insights regarding the primary role of self-regulators of biofilm formation in interspecies interaction and bacterial evolution.
