Bacillus subtilis Biofilms: a Matter of Individual Choice.

Bacillus subtilis has the capacity to choose between two mutually exclusive lifestyles: biofilm formation and flagellum-mediated swimming motility. Interestingly, this choice is made at the individual cell level, with bacterial cells in a population expressing genes required for biofilm formation or genes required for swimming motility but not both. A bistable switch controls the biofilm-versus-swimming decision, resulting in an evolutionarily favorable strategy known as "bet hedging" that ensures that subpopulations of bacteria continue to grow as conditions change and/or become unfavorable. In a recent issue of mBio, J. Kampf and colleagues (mBio 9:e01464-18, 2018, https://doi.org/10.1128/mBio.01464-18) reported the use of a combination of genetics and microfluidics to reveal that the interplay that occurs between the SinR and YmdB proteins underlies the B. subtilis choice between biofilm formation and swimming motility. Their report suggests that B. subtilis experiences selective pressure to form biofilms while maintaining reserve cell subpopulations with the capacity to swim away.