Bacillus subtilis is a
soil bacterium that plays a fundamental role in shaping the ecosystem of their
habitat. As such it is exposed to unavoidable interspecies interaction. We
chose to study the interactions between Bacillus subtilis and closely
related Bacillus firmus, competing for the same ecological niche -
the soil. Both species were capable of forming architectonically complex
multicellular colonies, also known as complex biofilms. Dramatically, as the
proximity between the two biofilms increased, B. subtilis enclosed the B.
firmus biofilm in a well-designed bacterial circling. The circling required
optimal production of the biofilm extracellular proteionous components, and
induction of bacterial motility. The engulfment of the rival colony led to the
death of the surrounded B. firmus cells within the biofilm. Surprisingly,
a subpopulation of the attacked B. firmus biofilm was able to
survive the B. subtilis attack, incorporate into the B. subtilis biofilm,
and sometimes to divide within this newly occupied niche. We suspect that the
antagonistic interaction with B. subtilis resulted in rapid evolution of
the attacked Bacillus firmus.
Our work offers new insight regarding the role of interspecies interactions between biofilms in the evolution, as part of the arm race between rival microbes in the soil.
