Surfing of bacterial droplets: Bacillus subtilis sliding revisited

Abstract

Hennes et al. (1) report on the collective slipping ofBacillus subtilis colonies across the agar surface, termed?colony surfing.? We read this article with great interest.However, we understand that specific points require amore detailed discussion. We would like to highlightcomplementary biological observations on this area previouslypublished by us and others but omitted byHennes et al. (1) with the aim of bringing about a commonterminology that facilitates understanding betweenthe biophysics and the microbiology communities. Bacterial movement on surfaces can be powered byvarious active appendages, such as flagella, pili, orinteraction of cytoskeletal and focal membrane complexes,but can also be driven by passive factors (2?4).Hennes et al. (1) report that B. subtilis droplets surf downagar surfaces independently of the presence of flagella,by recruiting water from the environment to these movingcolonies, lowering surface tension, and enhancingsubstrate wettability. Importantly, this process is demonstratedto be dependent on surfactin production.