Group post (AH, ER, EQ): Proof of the importance of TEP in biofilm formation

Transparent exopolymer particles (TEPs) are microgels of organic material consisting of very sticky particles that range in size from 0.4 to 200 μm. TEPs are formed from substances released by phytoplankton and bacteria as well as degradation of detritus and marine/freshwater snow. These particles are found in all aquatic environments and act like a glue, forming aggregates of particles with phytoplankton, bacteria, mineral clays and other particles. A recent study by Bar-Zeev et al. (2012) proposed a revised paradigm for aquatic biofilm development that emphasizes the critical role of microgel particles such as TEPs and ‘protobiofilm’ (TEPs with extensive microbial outgrowth and colonization) in facilitating this process.

Classic biofilm formation model

Biofilms are sessile colonies of microbes attached to a substrate and bound together within a matrix of mucile extracellular polymeric substances (EPS). First a thin conditioning film of less than 300μm is formed when dissolved organic polymers in the water column stick to a surface. Bacteria in the water column that encounter this film stick to it and are held in place by weak electrostatic forces and hydrophobic interactions. Using the DOM within the film as a source of nutrition, the bacteria rapidly multiply, produce EPS and the organised structure of the biofilm starts to take place.

Methods and materials write up:

The method was novel so important to mention. Samples of surface seawater were collected from Israel. Microscopy flow cells were the main apparatus used- please see Fig. 1. A glass upper surface inner plate permitted the formation and observation of biofilms as the water samples passed from the sample reservoir to the waste collection. Additionally, microscopic light and fluorescent observation was performed on the water sample moving through the flowcell. A port for adding stains to the sample is positioned at the beginning of the flow cell for use as and when required. Further examination with the use of CLSM (confocal laser-scanning microscopy) and AFM (atomic force microscopy) was conducted on  biofilms forming upon the removable silica inserts. Staining with the application of Alcian blue and Syto 9 (green) enabled the visualisation of bacteria, TEP’s and microgel clusters. With one piece of machinery- you can make three different observations! However it was unfortunate they didn’t identify any species bacteria and Archaea that could help in further investigations.

Fig. 1. Schematic overview of the flow-cell and experimental setup (see Materials and Methods for details).

 

Revised paradigm of biofilm translation

Bar-Zeev et al. discovered that the conditioning of a “pristine” surface begins immediately when exposed to seawater-organic polymers, colloids, microgel particles such as TEPS and protobiofilm adhere to the surface. During the first 30 minutes, more TEPs and protobiofilm particles attach firmly to the surface. If conditions remain favourable, a network of early mature biofilm forms from TEPs and protobiofilm. Over the next few hours bacteria that are attached to the associated microgels and single bacteria that attach to the biofilm start growing and producing EPS (such as standard biofilm model). The particles both quickly adhere but also cause changes in the surface adhesion and near-surface flow properties, which increases the probability of other particles and bacteria from the overlying water attaching to the biofilm.

This has implications for biofilm development and removal. Biofilms are very difficult to remove once established and the formation of a complex EPS matrix offers protection from biocides, chlorination and antibiotics. Fouling aquatic biofilms have become a real concern in many industries, such as water treatments, healthcare, as well as fouling surfaces in marine and freshwater environments. This study has highlighted the importance of planktonic microgels and protobiofilm in the initial stages of biofilm formation, which may aid in focusing research to prevent biofilm formation in areas that cause significant health risks.

Reference: Bar-Zeev, E., Berman-Frank, I., Girshevitz, O., & Berman, T. (2012). Revised paradigm of aquatic biofilm formation facilitated by microgel transparent exopolymer particles. Proceedings of the National Academy of Sciences,109(23), 9119-9124.

Find here: http://www.pnas.org/content/109/23/9119.short