Bacterially speaking: The application of quorum sensing inhibitors in marine biofouling

In the marine environment, all natural and artificial substrata are quickly colonised by micro- and macro- organisms, a process called biofouling. This can be particularly troublesome for ships, increasing drag, promoting metal corrosion and reducing transfer efficiency of heat exchangers. In 1987, mussel biofouling alone cost the US Navy more than 200 million dollars in the areas of hull scraping and excess fuel consumption from unnecessary drag on large vessels Morgan (1990). In the past, toxic coatings such as tributyltin (TBT) have been used to prevent biofouling, however, such coatings are toxic, causing significant harm to marine life. In light of this, much research has been put in to alternative, biologically friendly methods.

Dobretsov et al. (2011) tested 78 natural products for their ability to inhibit quorum sensing (QS), using a reporter, without causing toxicity. 24% of the chemicals tested inhibited QS without any measurable signs of toxicity, from these 24%, the most potent and abundant were further investigated using a luminescent LuxR-based reporter E. coli pSB1075. The cognate AHL was added in the presence of these chemicals and any reduction in luminescence was noted, results indicated that demoxy-encecalin, hymenialdisin at concentrations > 6.6 μM and 15 μM, respectively. Furthermore, luminescence was completely inhibited by Hymenialdisin and demoxy-encecalin, microlins A and B and kojic acid at concentrations of >0.2 μM, 2.2 μM, 1.5 μM, 15 μM and 36 μM respectively.

The ability to prevent microfouling by one compound, kojic acid at concentrations of 330 μM and 1 mM, was tested in controlled mesocosm experiments. Results showed that bacterial and diatom communities, on glass slides, where decreased in density when comparison with controls lacking kojic acid.

An earlier study by Dobretsov et al. (2007) also showed that using QS blockers can also control larval settlement indirectly by regulating the microbial community structure of biofilms and the density of bacteria, which in turn affects larval behaviour.

These two studies show that QS blockers have potential as biologically friendly anti-fouling compounds, through either the direct inhibition of QS, or indirectly, by altering laval settlement behaviour. I chose to review this paper because it recognises another application for QS inhibition, also known as quorum quenching (QQ). To me many scientists seem blinded by the possible application of QQ as a novel treatment for pathogenic bacteria, and forget that QS controls many different phenotypes, not just the presence of virulence factors.

Furthermore, if anyone else has found studies discussing alternative applications for QQ compounds, I would be very much interested.

Both studies can be found below:

1.           Dobretsov S, Dahms H-U, Yili H, Wahl M, Qian P-Y. 2007. The effect of quorum-sensing blockers on the formation of marine microbial communities and larval attachment. FEMS microbiology ecology 60:177–88.

2.           Dobretsov S, Teplitski M, Bayer M, Gunasekera S, Proksch P, Paul VJ. 2011. Inhibition of marine biofouling by bacterial quorum sensing inhibitors. Biofouling 27:893–905.

Morgan D. 1990. Two firms race to derive profits from mussels glue: despite gaps in their knowledge of how the mollusk produces the adhesive, scientists hope to recreate it. Scientist 4, 1