Microorganisms - ENVIS Centre

Marine biofouling is the result of the growth of microorganisms, plants and animals on surfaces immersed in the natural environment. The organisms involved in marine fouling are primarily attached or sessile forms commonly occurring in shallow waters along the coastline. The biofouling process occurs in the natural environment in sequential steps. Within minutes of immersion, a pristine surface becomes ‘conditioned’ through the adsorption of organic layers of macromolecules. The conditioned surface is later colonized by microorganisms, including bacteria, algae (especially diatoms), fungi and protozoa. The attachment, colonization and growth of microorganisms on the surface results in the formation of a slimy layer called biofilm. The biofilm layer can aid (or deter) the subsequent succession of ‘macrofouling’ species, such as barnacles, by facilitating adhesion or through the production of bioactive molecules (D’Sousa et al., 2010).

Biofouling is an ongoing problem for water-immersed man-made structures such as ship’s hulls (Fig. 1), oceanographic instrumentation, pipelines, membranes, heat exchangers and aquaculture equipment, resulting in severe economic consequences (Schultz, 2007). Biofouling (Figs. 2 & 3) is especially economically significant on ship hulls where high levels of fouling can reduce the performance of the vessel and increase its fuel requirements. Fouling causes huge material and economic costs in maintenance of mariculture, shipping industries, naval vessels, and seawater pipelines. Governments and industry spend more than US$ 5.7 billion annually to prevent and control marine biofouling. Biofouling can also occur in groundwater wells where build - up can limit recovery flow rates, and in the exterior and interior of ocean -laying pipes. In the latter case it has been shown to retard the seawater flow through the pipe and has to be removed with the tube cleaning process. Biofouling also occurs on the surfaces of living marine organisms, when it is known as epibiosis.

In efforts to avoid marine biofouling, antifouling paints are used, mostly with organotin like tri-n-butylin (TBT), in which copper and organonitrogen compounds as very effective active agents. The worldwide use of TBT - based paints has caused a growing pollution in the environment and in foods on a worldwide scale and also banned the use of TBT. At present, a major challenge for the producers of coatings is to develop alternative technologies to prevent fouling on ship hulls. Safer methods of biofouling control at the research level are use of copper compounds in paints and its continued use as metal sheeting (for example Muntz metal which was specifically made for this purpose), though there is still a debate on the safety of copper. The Office of Naval Research (ONR) has developed environmentally safe biomimetic ship coatings that protect against both barnacles and biofilms. Due to increasing restrictive regulations on the use of TBT and other polluting antifouling compounds, there is a growing need for other methods to prevent marine biofouling (Gademann, 2007).

Several physical, mechanical, chemical and biological methods for the prevention of marine biofouling have been tested in the last 40 years (Abarzua et al., 1999). The production and isolation of biogenic agents from marine organisms and their embedding in non - poisonous coatings seems to be the most promising and effective method for the prevention of marine fouling. Many marine organisms especially microalgae and marine invertebrates produce biogenic agents with antibacterial, antifungal, antialgal, antiprotozoan, antilarval and antimolluscidal property to defend themselves against settlement in the marine environment and are therefore rarely fouled by other organisms. Some of these secondary metabolites possess potent antifouling activity (Clare, 1996), but their antifouling activity under laboratory and field conditions are unknown.

Actinomycetes are a group of Gram - positive bacteria which form filamentous structure with asexual spores and have high Guanine plus Cytosine (G+C) content in their DNA. Diversity of actinomycetes in various natural and man-made ecosystems is well documented in recent years. Actinomycetes are primarily recognized as a source for high value metabolites such as antibiotics, antivirals, anticancers, enzymes and recombinant products in which most of them are of terrestrial origin (Balagurunathan and Radhakrishnan, 2007). Recently marine derived actinomycetes are also under exploitation especially for antibiotics and anticancer agents. In the past 10 years, 659 marine bacterial compounds have been described with majority derived from actinomycetes (Williams, 2009). As marine environmental conditions are extensively different from terrestrial ones, the marine actinomycetes are different from those of terrestrial strains in producing different types of bioactive compounds. Unique compounds like salinosporamide and abyssomycin from marine actinomycete genera Salinispora and Verrocosispora add a new dimension to marine natural product research. Unfortunately actinomycetes in general and marine actinomycetes in particular are less / unexploited as antifouling compounds.

The first step in laboratory antifouling research work is the isolation of biogenic compounds and their testing on the growth of fouling organisms. Till date, antifouling compounds are reported from marine organisms like bacteria, algae and certain plants; but such reports from marine actinomycetes are scanty. An antifouling diketopiperazine was reported from deep sea bacterium Streptomyces fungicidicus (Li et al., 2006). You et al. (2007) studied inhibition of Vibrio biofilm formation by a marine actinomycete A66, Streptomyces albus. Recently, Xu et al. (2010) isolated five structurally similar compounds from the crude extract of a marine Streptomyces strain obtained from deep - sea sediments. Antifouling activities of these five compounds and four other structurally - related compounds isolated from a North Sea Streptomyces strain against major fouling organisms were compared to probe structure - activity relationships of compounds. The functional moiety responsible for antifouling activity lies in the 2 - furanone ring and that the lipophilicity of compounds substantially affects their antifouling activities. Based on these findings, a compound with a straight alkyl side - chain was synthesized and proved itself as a very effective non - toxic, anti - larval settlement agent against three major fouling organisms. The strong antifouling activity, relatively low toxicity, and simple structures of these compounds make them promising candidates for new antifouling additives. Therefore, isolation of biogenic compounds from actinomycetes and determination of their structures could provide leads for future development of environment - friendly antifouling paints.

In the future, progress in the field of isolation and production of antifouling compounds is expected to involve the integration of biochemistry validated post - genomic methods and technologies and intelligent bioprocess design.

One of the most important things for developing antifouling compounds from marine actinomycetes is that they must meet the standard of the EC Biocide Directive for registered toxins. There is a need to investigate the levels of toxicity and capacities for biological degradation in the aquatic environment of actinomycetes compounds before they are used in antifouling paints and polymers for the prevention of fouling.

Moreover, it is necessary to monitor it over a long term period, once the actinomycetes compounds become incorporated into antifouling paints. This is beginning, as trials have shown that paints into which extracts of marine actinomycetes have been incorporated are effective in controlling foulers in the marine environment. However, the identification of these actinomycetes compounds with antifouling properties requires a wide range of expertise from the field of biology as well as chemistry. Due to this, antifouling compounds from marine actinomycetes with commercial potential will take time to develop. Metabolic engineering approaches are the possible way forward for future exploitation of secondary metabolites with antifouling properties from marine actinomycetes.

Abarzua, S., Jakubowski, S., Eckert, S. and Fuchs, P. (1999) Biotechnological investigations for the prevention of marine biofouling. II. Blue Green Algae as potential producers of biogenic agents for the growth inhibition of macrofouling organisms. Botanica Marina. 42, 459 - 465.

Balagurunathan, R. and Radhakrishnan, M. (2007) Actinomycetes: Diversity and their importance - An overview in microbiology - Applications and current trends (editor) P.C.Trivedi, Pointer publishers Rajasthan. 297 - 329.

Clare, A. S. (1996) Marine natural product antifoulants: status and potential. Biofouling. 9, 211 - 229.

D’Sousa, F., Bruin, R., Blerstekar, A., Donnelly, G., Klijnstra, J., Rentrop, C. and Wiilemsen, P. (2010) Bacterial assay for the rapid assessment of fouling and fouling release properties of coatings and materials. J. Ind. Microbiol. Biotechnol, 37, 363 - 370.

Gademann, K. (2007) Cyanobacterial natural products for the inhibition of biofilm formation and biofouling. Chimia, 61, 373 - 377.

Li, X., Dobretsov, S., Xu, Y., Xiao, X., Hung, O. S. and Qian, P. (2006) Antifouling diketopiperazines produced by a deep - sea bacterium, Streptomyces fungicidicus, Biofouling, 22(3), 187 - 194.

Schultz, M. P. (2007) Effects of coating roughness and biofouling on ship resistance and powering. Biofouling, 23, 331 - 341.

You, J. L., Xue, X. L., Cao, L. X., Lu, X., Wang, J., Zhang, L. X. and Zhou, S. N. (2007) Inhibition of Vibrio biofilm formation by a marine actinomycete strain A66. Appl. Microbiol. Biotechnol, DOI; 10.1007/s00253 - 007 - 1074.

Williams, P.G. (2009) Panning for chemical gold: marine bacteria as a source of new therapeutics. Trends in Biotechnology, 27, 45 - 52.

Xu, Y., He, H. , Schulz, S., Liu, X., Fusetani, N. and Xiong, H. (2010) Potent antifouling compounds produced by marine Streptomyces. Bioresource Technology, 101:1331 - 1336.