EPS from one microbe prevents settlement and production of EPS by another

Guezennec, J., Herry, J., Kouzayha, A., Bachere, E., Mittelman, M., Fontaine, M. (2012) Exopolysaccharides from unusual marine environments inhibit early stages of biofouling. International Biodeterioration & Biodegradation. 66.

A big problem for structures in the marine and freshwater
environment is the formation of biofilms and then the subsequent biofouling
that involves macro-organisms. Prevention strategies using antimicrobials often
also effect non-target organisms and are therefore harmful to the environment.
This research supports the notion that microbes that colonize a surface excrete
chemicals contained in exopolysaccharides
(EPS) to prevent other microbes colonizing the material instead. The primary coating of surfaces by specific exopolysaccharides (EPS) produced by biofilm forming bacteria,
inhibited biofilm formation. This study evaluated the antifouling potential of several
exopolysaccharides produced by bacteria originating from unusual marine
ecosystems. The authors did not explain why unusual environments were best to
look in but said that five significant EPS producers have been identified
from Alteromonas, Pseudoalteromonas, Pseudomonas, Vibrio and Pyrococcus spp
already.

Screenings performed on 500 isolates led to the
discovery of a number of microbial EPSs with interesting chemical and
rheological properties. The model surface was a glass plate, which is a
relatively hydrophilic material, to avoid surface reactions that might
interfere with the adhesion data collected (e.g., corrosion and thus the
presence of surface defects that could influence adhesion of microbial cells). Microbial adhesion assays were performed with a
custom-made flow cell system. Adhering bacteria were photographed after
sequential periods of up to 10 min and the percentage of bacteria adhering to
the glass surface was determined as well as the initial deposition rate.

Several authors have reported that
exopolysaccharides had antimicrobial effects against various bacteria but this
study did not find any evidence of this or cytotoxicity. This may be the
result of both different methodologies (i.e., culture conditions) and resulting
active molecules. On the glass surfaces with very low concentrations of the
different EPSs, bacterial colonization did not exceed 20% of the total surface
area compared to a coverage of 70% on the controls.

The presence of a polymeric film on a
surface can induce changes in the hydrophobic/hydrophilic balance.
Microorganisms have been generally found to attach more rapidly to hydrophobic
and non-polar surfaces than hydrophilic surfaces. Extra cellular
polysaccharides, proteins and DNA are highly hydrated hydrophilic molecules and
therefore this may be the mechanism of biofilm formation.

This study is exploring a novel antifouling technology
that could be a non-toxic solution to biofouling. Biofilm bacteria use EPS to
stick to the surfaces and therefore the application of EPS products to structures
should be successful, although the authors did not elaborate on this. It is
difficult to get an antifoulant to remain on the surface its treating, and
contamination of the environment occurs when it is washed off. A 50% reduction
in biofilm coverage is a promising result but large scale and longer duration
experiments are required to see if this has full potential. The paper mentions
what the EPS contained but does not explain what roles these substituents are
having, suggesting the mechanism is unclear.