biofilm 2Featured top Image. Reverse Osmosis membranes in a full-scale desalination membrane. Insert shows biofouling on membranes.


Fig 1. Schematic illustration showing the involvement of organic polymers and colloids, TEP and protobiofilm in the initial stages of aquatic biofilm formation.  Immediately upon exposure to seawater, organic polymers and colloids (a) and microgels such as uncolonized TEP (b) and protobiofilm (c) begin to attach to pristine surfaces. Single cells of planktonic bacteria also attach reversibly (d) or irreversibly (e) to conditioned surfaces. With time (minutes to hours) a contiguous coverage of mature biofilm (f) develops. From Bar-Zeev et al. 2013.PNAS

Limitations of global freshwater supplies have stimulated the application of desalination technology with desalinized water coming online worldwide at a rate of 40 to 50 million m3 d−1. Currently, about 50% of global desalination is based on filtration through reverse osmosis (RO) membranes requiring effective pretreatment procedures upstream to reduce fouling, maintain performance and extend membrane lifetime and to ensure the manufacturers requirements for membrane recovery yield.

Transparent exopolymer particles (TEPs) are sticky, organic microgels, ranging in size from ∼0.4 to >200 μm, present in large numbers in all aquatic environments. Recently, TEPs have been implicated as an important factor in the development of aquatic biofilm and are part of the extracellular polymeric substances (EPSs) that form the matrix of microbial biofilms.
In our research we examined the direct involvement of these microgel particles in biofilm development. We showed that protobiofilm and TEPs in the feedwater contributed to fast development of biofilm and not EPSs generated by adhering, single bacteria, or bacterial aggregates. In addition, experiments comparing the initial stages of biofilm formation in filtered or in untreated seawater clearly illustrate the importance of protobiofilm and TEPs in accelerating aquatic biofilm formation.