Rhamnolipid, another application

I have spoken about the uses of rhamnolipids, a biosurfactant, before and this paper goes on to talk about their potential to disrupt biofilms from surfaces exposed to the marine environment, a simple but generally unexplored area. Specifically this paper focuses on the biofilm crated by Bacillus pumilus and the effect of rhamnolipid on its ability to adhere to steel. Many Bacillus species are resistant to harsh environmental conditions such as low nutrient availability and UV radiation and this hardiness also means they are able to resist anti- fouling biocides. Adhesion to steel and the production of sticky exopolysaccharides and organic acids by Bacillus biofilm leads to increased corrosion and thousands of dollars’ worth of damage. Primary colonizing bacteria are the first to adhere to such surfaces and so the killing and ideally the removal of such is an important problem in need of a solution, biosurfactants could act as that solution.

B. pumilus were allowed to adhere for 4 hours at 30°C. Different concentrations (0.05 – 100mM) of rhamnolipid were then added to the polystyrene microtitre plates and left for a further one hour. After staining the results were taken as a percentage of cell adhesion compared to control plates which were not treated with rhamnolipid.

Exopolymeric substances (EPS), which have been investigated in other blogs, are the basis for adhesion of cellular substances to surfaces underwater. They allow for the attachment of other species leading to a community of microbes ultimately creating a damaging biofilm. Rhamnolipids have been shown to have antimicrobial as well as surfactant properties against other bacteria such as B. subtilis and Staphylococcus epidermis at low minimum inhibitory concentrations (<1.6 mM MIC) however the growth of B. pumilis in this case was not inhibited until >1.6mM and therefore higher concentrations of rhamnolipid are needed compared to other Gram negative bacteria. In contrast to this, at low concentrations, rhamnolipid significantly inhibited the adhesion of 46 – 99% of B. pumilus, after one hour there was at least 80% inhibition of adhesion to the polystyrene surfaces which may be enough to prevent the formation of biofilm. Other tests with different bacteria also show the effectiveness of rhamnolipid as an anti – adhesive when it comes to biofilm.

EPS is thought to neutralize antimicrobial agents and therefore assist the microbial community form dangerous biofilm. Therefore the disruption of such EPS could stop such formation. At higher concentrations than the MIC value there was a significant dose – dependent increase in biofilm disruption after treatment with rhamnolipid. After one hour there was significant EPS disruption and 24hours treatment led to destruction of microcolonies. One problem with this report is the suggestion that rhamnolipid usage would be more successful with the help of biocides. In the marine environment the use of biocides in unattractive due to other environmental hazards this brings about. However, the treatment of rhamnolipids does have potential and should be investigated further.

Review of Dusane et al (2010) Rhamnolipid mediated disruption of marine Bacillus pumilus biofilms