High osmotic stress initiates expansion and detachment of Thalassospira sp. biofilms in glass microchannels

Abstract

Control of microbial activity and biofilm growth is an essential factor in a variety of medical and industrial applications. As microbial biofilms can protect cells within from physical or chemical threats, biocide treatments are often limited in their efficiency due to the low permeability of the biofilm. Therefore, finding new treatment options against biofilms remains an issue of high importance. We explored the option of using osmotic pressure to physically deform the biofilm matrix and increase detachment from a glass surface. Our model system is a single-species biofilm of Thalassospira sp. growing in a microfluidic set-up, enabling the observation of changes in biofilm volume and detachment rate. We observed that injection of a high salinity brine (NaCl) led to a reduction of biofilm volume (water efflux), and that subsequent injection of low salinity brine caused biofilm expansion (water influx). The differential osmotic pressure imposed on the biofilm was sufficient to weaken its adhesive strength to the glass surface, causing major detachment. The current approach has value as a method for cleaning glass microfluidic channels and other glass tubing or equipment clogged by biofilms, thus avoiding the use of harsh chemicals. As the basic physical principle of osmotic pressure initiating biofilm expansion and detachment is universal, our findings could be applied to other forms of biofilm growth.