Slimy Libraries

Biofilms are excellent habitats for microorganisms to live in as they provide protection against stresses like UV radiation, biocides, desiccations, heavy metals etc. A biofilm is primarily made of extracellular polymeric substances (EPS) which is secreted by microorganisms. The diversity seen in microorganisms reflects the diversity in different EPS’s secreted, each species of bacteria creating an EPS with a unique physical structuring lending specific properties to each EPS. This structural diversity makes marine EPS a potential source for commercial application, however few types of EPS have been characterised. Before tests can be done on the potential of different EPS’s a library must first be built. The purpose of this study was to quantify the EPS produced by two early colonising Vibrio species; V. campbellii, and V. fortis. The EPS was isolated, characterised, compared and their rheology (the study of the flow of matter and response of solids to an applied pressure) and emulsifying potential was studied.

The emulsion of exopolymers produced by both Vibrio’s in this study had similar capabilities, but compared to previous studies on V. parahaemolyticus the EPS was less stable, although more stable thanes made by V. harveyi. The EPS of V. campbellii consisted of five sugars (arabinose, galactose, glucose, mannose and rhamnose) whereas V. fortis was made of only three (arabinose, galactose and mannose). Using scanning electron microscopy and atomic force microscopy biofilms the biofilm produced by V. campbellii was smooth, compact and firmly attached with bacteria whereas V. fortis produced a biofilm that was loosely bound with bacteria and irregularly shaped, although the exopolymer itself was compact and porous. The authors conclude that V. campbellii is a faster growing, producing more EPS but less efficient in biolfilm formation as compared to V. fortis. However, this seems contradictory to the SEM analysis, unless having an irregularly shaped biofilm is more efficient? This was not fully discussed in the paper, indeed much of the ‘results and discussion’ section was lacking in discussion!

The paper was an interesting read, however the impact of the results could have been discussed further. The need to build an EPS library is an important task, however first there should be standards set for the measurement of different EPS. The experiments done in this study did provide information about the composition and fluidity, but for industrial uses strength should also be quantitatively measured.

Kavita, K., Mishra, A. & Jha, B. (2013) Extracellular polymeric substances from two biofilm forming Vibrio species: Characterization and applications.