Enhanced erosion resistance of biopolymer-enriched B. subtilis NCIB 3610 biofilms

<p>Erosion resistance is one of the advantages bacteria gain by producing biofilms. While it is undesirable for us humans when biofilms grow on medical devices or industrial pipelines, biofilms with a high erosion resistance can be advantageous for biotechnological applications. Here, we demonstrate how the erosion resistance of <em>B. subtilis</em> NCIB 3610 biofilms can be enhanced by integrating foreign (bio)polymers such as γ-polyglutamate (PGA), alginate and polyethylene glycol (PEG) into the matrix during biofilm growth.<br /><br />Artificial enrichment of the NCIB 3610 biofilms with these biopolymers causes a significant increase in the erosion resistance by slightly changing the surface topography: A decreased cavity depth on the surface results in an alteration in the mode of surface superhydrophobicity, and we obtain a state that is located somewhere between rose-petal like and lotus-like wetting resistance. Surprisingly, the viscoelastic and microscopic penetration properties of the biofilms are not affected by the artificial incorporation of (bio)polymers. As we obtained similar results with all the biopolymers tested (which differ in terms of charge and molecular weight), this indicates that a variety of different (bio)polymers can be employed for a similar purpose.<br /><br />The method introduced here may present a promising strategy for engineering beneficial biofilms such, that they become more stable towards shear forces caused by flowing water but, at the same time, remain permeable to nutrients or other molecules.</p>

OVERFLOWING TESTS AT THE POLISH DREDGDIKES RESEARCH DIKE – STABILITY OF THE DIKE SURFACE AGAINST EROSION

In the project DredgDikes the different research dike embankments were tested with respect to overflowing water induced erosion. Therefore, flumes were installed on the land side embankments in which the effect of overflowing water on the vegetated surface was investigated. On the Polish DredgDikes research dike near Gdansk, Poland, two parallel flumes were installed and the surface of the dike made of different mixtures of ash, silt and sand as well as clay was tested both in vegetated and unvegetated state. The results showed that the grass sods placed on the dike embankment had a comparably low erosion stability, particularly if placed directly on the hardened ash/silt dike cover with better results if placed on a clay cover, while the ash/silt mixture showed a high erosion resistance without vegetation. This results in the recommendation to use a thicker vegetation layer on top of the ash composite dike if the vegetation shall account for the erosion resistance or else, that even if the grass cover is washed away, a very solid cover made of the ash composite can withstand an overflowing event for considerable time.