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Bacteria and Cyanobacteria
promote and prevent fouling
Hans-U. Dahms
Institute of Marine Biology
National Taiwan Ocean University (NTOU).

Biofilms on marine underwater surfaces can promote or inhibit the settlement of other micro- and macrobiota, such as macroalgal spores and invertebrate larvae. The settlementmediating effects of biofilms probably involve a variety of biofilm attributes, including surface micro-topography and chemistry, as well as a wide range of microbial products from small metabolites to high-molecular weight extracellular polymers. The settled organisms in turn can modify microbial species composition of biofilms and thus change the biofilm proper t ies and dynami c s . A bet ter understanding of biofilm dynamics and chemical signals released and/or stored by biofilms will facilitate the development of antifouling and of mariculture technologies alike.

A biofilm itself is distinguished from other types of microbial aggregations by its formation at interfaces. In euphotic marine environments biofilms mainly consist of phototrophic and heterotrophic bacteria, and diatoms. Microbial cells in biofilms are enmeshed in a matrix of extracellular polymers (EPS) that are mainly composed of highmolecular weight polysaccharides.

The structure of biofilms is complex and three-dimensional. Gram-negative bacteria in biofilms produce cell-to-cell communication signals (quorum sensing signals) having effects on bacterial biofilm formation. A broad range of marine invertebrate larvae utilize biofilms as indicators of substratum suitability for prospective settlement. Since the formation of biofilms on newly submerged substrata as a rule precedes colonisation by invertebrates, the establishment of microbial biofilms is regardedas a general prerequisite for the colonization of macroorganisms such as invertebrate larvae and algal spores.

Current antifouling technologies are based on the application of toxic substances that can be harmful to the natural environment. For this reason and the global ban of tributyl tin (TBT), there is a need for the development of ''environmentallyfriendly'' antifoulants. Marine microbes are promising potential sources of non-toxic or lesstoxic antifouling compounds as they can produce substances that inhibit not only the attachment and/or growth of microorganisms but also the settlement of invertebrate larvae and macroalgal spores. Cyanobacteria are much neglected in this respect, although they produce a variety of bioactive metabolites that may have allelochemical functions in the natural environment, such as in the prevention of fouling by colonizing organisms.

Chemical compounds from cyanobacteria are also of biotechnological interest, especially for clinical applications, because of their antibiotic, algicidal, cytotoxic, immunosuppressive and enzyme inhibiting activities.

Cyanobacterial metabolites have the potential for use in antifouling technology, since they show antibacterial, antialgal, antifungal and antimacrofouling properties, which could be exploited in the prevention of biofouling on madmade substrates in the aquatic environment. Molecules with antifouling activity represent a number of types including fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles and steroids. The isolation of biogenic compounds and the determination of their structure may provide leads for future development of, for example, environment friendly antifouling paints. An advantage of exploring the efficacy of cyanobacterial products is that the organisms can be grown in mass culture, which can be manipulated to achieve the optimal production of bioactive substances. Phycotoxins and related products from cyanobacteria may serve as materials for antimicro- and antimacrofouling applications.

Further readings:

Dahms H-U, Xu Y & Pfeiffer C (2006) Antifouling substances from cyanobacteria. Biofouling 22(5): 317-327.

Dobretsov S, Dahms H-U & Qian P-Y (2006) Inhibition of biofouling by marine microorganisms and their metabolites. Biofouling 22(1): 43-54.

Qian P-Y, Lau SCK, Dahms H-U, Dobretsov S & Harder T (2007). Marine biofilms as mediators of colonization by marine macroorganisms: implications for antifouling and aquaculture. Marine Biotechnology X: 1-12 DOI: 10.1007/s10126-007-9001.

For more details contact:

Hans-U. Dahms Institute of Marine Biology National Taiwan Ocean University (NTOU) 2, Pei-Ning Road, Keelung 202, Taiwan 0224, R. O. C. Tel: 886-2-2469-8084; Fax: 886-2-24629464 E-mail: hansd@ntou.edu.tw
ENVIS CENTRE Newsletter Vol.6,No 1 March 2008 Back 
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