Natural Antifouling compounds from cyanobacterium Lungbya majuscule

The current most widely used method of boifouling control in marine environments involves the use of highly toxic compounds. Use of these chemicals is undesirable due to their highly toxic nature which can affect marine life. It is therefore desirable to find an alternative form of control. Many potential marine-derived antifoulants have been identified from organisms which are naturally exposed to larvae of fouling organisms and produce anti-fouling chemicals. Synthetic analogues of such naturally produced antifoulants can be developed and mass produced for commercial use.

Cyananobacteria are known to produce many useful secondary metabolites but few have been looked at for possible antifouling (AF) properties.  These secondary metabolites have been shown to possess useful antifeed properties against fish, herbivores and marine invertebrates. Some secondary metabolites identified from Lyngbya majuscule have been shown to possess such antifeed properties and the authors hypothesised that these compounds may inhibit invertebrate larval settlement.  In this study twelve secondary metabolites were purified from L. Majuscula and their effect on barnacle larvae settlement was assessed. Some metabolites were found to be highly toxic, killing more than 90% of the barnacle cyprids. Others showed significantly lower toxicity (<15%) and also showed high anti settlement activities ( >80% of the barnacle were unsettled). The best anti settlement molecule of the 12 tested was found to be dolistain 16 which was tested at many different concentrations and was found to have an EC₅₀ at 0.003 µg ml^-1.

Further evaluation of this molecule was carried out in the field at concentrations of 10.0, 1.0, 0.1 and 0.01 µg ml^-1.All four concentrations showed significant AF activities against the settlement of barnacles. Plates containing dolastatin 16 at a concentration of 10.0 µg ml^-1 showed barnacle counts below 25 individual and 0.01 µg ml^-1  showing  less than 100 individuals. When compared to the control with counts of greater than 200 barnacles it can be seen that a significant reduction in settlement occurs, at the lowest concentration. Therefore indicating that dolastain 16 is a highly effect inhibitor of barnacle settlement.

This study shows that cyanobacteria could be used in future as a source an environmentally friendly antifouling compounds and this group should be further explored to find more possible AF compounds. Prior to this study only one cyanobacterial secondary metabolite had been explored for possible AF properties therefore this study provided a valuable contribution to the field, widening the number of molecules tested. Secondary metabolites such as the ones tested in this study could provide an alternative to the current methods of antifouling control. Future work should focus on incorporation of molecules such as dolastin 16 into antifouling paints and further work is needed to assess the AF properties of other secondary metabolites to find the most appropriate.

 Lik Tong Tan , Beverly Pi Lee Goh , Ashootosh Tripathi , Mui Gek Lim , Gary H. Dickinson , Serina

Siew Chen Lee & Serena Lay Ming Teo (2010): Natural antifoulants from the marine cyanobacterium Lyngbya majuscula ,

Biofouling: The Journal of Bioadhesion and Biofilm Research, 26:6, 685-695

This paper can be found at: http://www.tandfonline.com/doi/pdf/10.1080/08927014.2010.508343