Exploitation of marine algae: biogenic compounds for potential antifouling applications

Marine algae are one of the largest producers of biomass in the marine environment. They produce a wide variety of chemically active metabolites in their surroundings, potentially as an aid to protect themselves against other settling organisms. These active metabolites, also known as biogenic compounds, produced by several species of marine macro- and micro-algae, have antibacterial, antialgal, antimacrofouling and antifungal properties, which are effective in the prevention of biofouling, and have other likely uses, e.g. in therapeutics. The isolated substances with potent antifouling activity belong to groups of fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles and steroids. These biogenic compounds have the potential to be produced commercially using metabolic engineering techniques. Therefore, isolation of biogenic compounds and determination of their structure could provide leads for future development of, for example, environmentally friendly antifouling paints. This paper mainly discusses the successes of such research, and the future applications in the context of understanding the systems biology of micro-algae and cyanobacteria.Abbreviations AHL Acylated homoserine lactone - TBT Tributyl tin     

Thermoplastic,rubber-like marine antifouling coatings with micro-structures via mechanical embossing

Abstract

New processing routes and materials for non-biocidal, antifouling (AF) coatings with an improved performance are currently much sought after for a range of marine applications. Here, the processing, physical properties and marine AF performance of a fluorinated coating based on a thermoplastic (non-crosslinked) fluorinated polymer are reported. It was found that the addition of lubricating oil and hydrodynamic drag reducing microstructures improved the AF properties substantially, i.e. the settlement of a marine biofilm, containing mixed microalgae including diatoms, was reduced to low levels. More importantly, the remaining fouling was removed from the coatings at low hydrodynamic shear rates and promising AF properties were obtained. Moreover, additional potential benefits were revealed originating from the thermoplastic nature of the coating material which might result in significant cost reductions.     

Selection of commercial hydrolytic enzymes with potential antifouling activity in marine environments

In this work, the marine antifouling potential of some commercially available hydrolytic enzymes acting on the main constituents of extracellular polymeric substances (EPS) involved in bacterial biofilm formation was determined. The selected protease (i.e., alpha-chymotrypsin from bovine pancreas), carbohydrase (i.e., alpha-amylase from porcine pancreas) and lipase (from porcine pancreas) exhibited remarkable hydrolytic activities towards target macromolecules typically composing EPS under a wide range of pHs (6.5-9.0 for alpha-chymotrysin and alpha-amylase; 7.0-8.5 for the lipase) and temperatures (from 10 °C to 30 °C), as well as relevant half-lives (from about 2 weeks to about 2 months), in a marine synthetic water. The activity displayed by each enzyme was poorly affected by the co-presence of the other enzymes, thus indicating their suitability to be employed in combination. None of the enzymes was able to inhibit the formation of biofilm by an actual site marine microbial community when applied singly. However, a mixture of the same enzymes reduced biofilm formation by about 90% without affecting planktonic growth of the same microbial community. This indicates that multiple hydrolytic activities are required to efficiently prevent biofilm formation by complex microbial communities, and that the mixture of enzymes selected in this study has the potential to be employed as an environmental friendly antifouling agent in marine antifouling coatings.     

Periodic ultraviolet-C illumination for marine sensor antifouling

Ultraviolet light has intriguing potential as a marine antifoulant, targeting almost any species and applicable to almost any surface, while not accumulating in the environment. This study field-tested the effects of periodic ultraviolet-C illumination on marine macrofouling. Across four experiments, several UV illumination duty cycles were tested against controls with no illumination. Duty cycles between 1:2 (time with UV:total time per cycle) and 1:20 were all similarly effective, inhibiting almost all macrofouling at three different temperate Northeast Pacific and Northwest Atlantic sites. Susceptible taxa included barnacles, bryozoans, tunicates (colonial and solitary), and, to a slightly lesser extent, mussels. Duty cycles of 1:30 and 1:60 reduced but did not eliminate biofouling. Measurements of ultraviolet illumination on oceanographic sensors showed similar results. The results suggest further investigation of ultraviolet light as an antifoulant for marine sensors, including susceptibility of other taxa, optimizing illumination patterns, and exploring the potential for evolved resistance.     

Poly(ethylene glycol)-containing hydrogel surfaces for antifouling applications in marine and freshwater environments

This work describes the fabrication, characterization, and biological evaluation of a thin protein-resistant poly(ethylene glycol) (PEG)-based hydrogel coating for antifouling applications. The coating was fabricated by free-radical polymerization on silanized glass and silicon and on polystyrene-covered silicon and gold. The physicochemical properties of the coating were characterized by infrared spectroscopy, ellipsometry, and contact angle measurements. In particular, the chemical stability of the coating in artificial seawater was evaluated over a six-month period. These measurements indicated that the degradation process was slow under the test conditions chosen, with the coating thickness and composition changing only marginally over the period. The settlement behavior of a broad and diverse group of marine and freshwater fouling organisms was evaluated. The tested organisms were barnacle larvae (Balanus amphitrite), algal zoospores (Ulva linza), diatoms (Navicula perminuta), and three bacteria species (Cobetia marina, Marinobacter hydrocarbonoclasticus, and Pseudomonas fluorescens). The biological results showed that the hydrogel coating exhibited excellent antifouling properties with respect to settlement and removal.     

Algal antifouling and fouling-release properties of metal surfaces coated with a polymer inspired by marine mussels

The marine antifouling and fouling-release performance of titanium surfaces coated with a bio-inspired polymer was investigated. The polymer consisted of methoxy-terminated poly(ethylene glycol) (mPEG) conjugated to the adhesive amino acid l-3,4-dihydroxyphenylalanine (DOPA) and was chosen based on its successful resistance to protein and mammalian cell fouling. Biofouling assays for the settlement and release of the diatom Navicula perminuta and settlement, growth and release of zoospores and sporelings (young plants) of the green alga Ulva linza were carried out. Results were compared to glass, a poly(dimethylsiloxane) elastomer (Silastic T2) and uncoated Ti. The mPEG-DOPA3 modified Ti surfaces exhibited a substantial decrease in attachment of both cells of N. perminuta and zoospores of U. linza as well as the highest detachment of attached cells under flow compared to control surfaces. The superior performance of this polymer over a standard silicone fouling-release coating in diatom assays and approximately equivalent performance in zoospore assays suggests that this bio-inspired polymer may be effective in marine antifouling and fouling-release applications.     

新型海洋防污剂应用组分的简述

海洋防污涂料是通过海洋防污剂的可控释放,与海洋污损生物发生作用,从而阻止海生物在物体表面附着。海洋防污涂料中最重要的组成部分是基体树脂和海洋防污剂。海洋防污剂主要是从农药、杀虫剂、杀菌剂、防霉剂以及带有生物活性的聚合物中筛选出来的,随着海洋环境保护日益严格,制备和筛选高效、广谱的海洋防污剂对海洋防污涂料的发展日显重要,本文对现有的防污剂材料作了简述。     

Pioneer marine biofilms on artificial surfaces including antifouling coatings immersed in two contrasting French Mediterranean coast sites

Marine biofilm communities that developed on artificial substrata were investigated using molecular and microscopic approaches. Polystyrene, Teflon? and four antifouling (AF) paints were immersed for 2 weeks at two contrasting sites near Toulon on the French Mediterranean coast (Toulon military harbour and the natural protected area of Porquerolles Island). Biofilms comprising bacteria and diatoms were detected on all the coatings. The population structure as well as the densities of the microorganisms differed in terms of both sites and coatings. Lower fouling densities were observed at Porquerolles Island compared to Toulon harbour. All bacterial communities (analysed by PCR-DGGE) showed related structure, controlled both by the sites and the type of substrata. Pioneer microalgal communities were dominated by the same two diatom species, viz. Licmophora gracilis and Cylindrotheca closterium, at both sites, irrespective of the substrata involved. However, the density of diatoms followed the same trend at both sites with a significant effect of all the AF coatings compared to Teflon and polystyrene.     

Global analysis of the carbon starvation response of a marine Vibrio species with disruptions in genes homologous to relA and spoT.

The stringent control response, which involves a rapid accumulation of ppGpp, is triggered if the marine Vibrio sp. strain S14 is subjected to carbon and energy starvation. By means of high-resolution two-dimensional gel electrophoresis analysis, we addressed the role of the major ppGpp-synthesizing enzyme (RelA) in the regulation of the carbon starvation response of Vibrio sp. strain S14. The finding that a large number of the carbon starvation-induced proteins were underexpressed in the Vibrio sp. S14 relA mutant strain after the onset of glucose starvation suggests that a rapid accumulation of ppGpp is required for induction of many of the carbon starvation-induced proteins. However, it was also found that a majority of the carbon starvation-induced proteins were significantly less induced if the stringent control response was provoked by amino acid starvation. We therefore also addressed the notion that a carbon starvation-specific signal transduction pathway, complementary to the stringent control, may exist in Vibrio sp. strain S14. It was found that a majority of the proteins that were underexpressed in the relA mutant strain were also underexpressed in the Vibrio sp. S14 spoT mutant strain (csrS1). Interestingly, a large proportion of these underexpressed proteins were found to belong to a group of proteins that are not, or significantly less, induced by starvation conditions that do not promote starvation survival. On the basis of these observations and the finding that the csrS1 strain survives poorly but accumulates ppGpp in a fashion similar to the wild type during carbon and energy source starvation, the gene product of the csrS gene is suggested to be responsible for the mediation of a signal which is complementary to ppGpp and essential for the successful development of the starvation- and stress-resistant cell. This conclusion was also supported by experiments in which changes in phenotypic characteristics known to be induced during carbon starvation were studied. The starvation induction of the high-affinity glucose uptake system was found to be dependent on the csrS gene but not relA, and the synthesis of carbon starvation-specific periplasmic space proteins was dependent, at different times of starvation, on both the relA and the csrS gene products.     

The use of stable isotopes to trace small-scale movements by small fish species

Valuable biological information can be obtained by monitoring the movement of organisms. However, the choice of monitoring method becomes highly restricted when following small organisms (<100 mm), especially in aquatic ecosystems. Stable isotopes are being increasingly used in this respect but rarely at the local spatial scale, i.e. 10–1000 s of metres. We sought to identify movement of small fishes between a main river channel and its tributary. Little overlap in isotope baseline was detected between the two channels despite some temporal variability in δ¹⁵N of baseline indicator organisms in the main river. The individuals of two small cyprinid fish species (Leuciscus souffia and Alburnoides bipunctatus) of all the size classes (40–100 mm) caught within the tributary showed considerable heterogeneity in δ¹⁵N values. Classification and discriminant analysis on isotope-derived data distinguished two significantly different groups. Moreover, this result was supported by further sampling of fish caught in the main river (in May and December 2006). Alternative hypotheses, such as dietary differences, biological factors, temporal shifts and spatial differences in diet, did not explain δ¹⁵N variability. This application of stable isotopes at a relatively small spatial and temporal scales further demonstrates its potential as a tool for ecologists.     

The potential of and limitations to marine population prognosis

Following the 19th century recognition and definition of basic ecological entities, functional analysis has been the highlight of this century. The synthesis of these findings enables ecological prognosis. The population as the basic functional unit has been repeatedly treated; in the marine field, fisheries management approaches developed into multi-species population analysis. As in planktology, theoretical ecology, and classic biocoenotic research, the population interactions are of increasing scientific interest. A mathematical model is suggested that combines these extrinsic and intrinsic functional relationships in order to define the fit of the ecological niche to the environment, the decisive measure of the expected population success, and thus of the probable population development needed for prognostic purposes. It is discussed in how far the orientation towards the predictive power or — with respect to the “skill” of meteorological prognoses — the “ecological prognostic skill” improvement may serve as a means to choose the best investigative strategy.     

Short-term testing of antifouling surfaces: the importance of colour

Data from short-term biofouling assays are frequently used to evaluate the performance of antifouling (AF) coatings. There are a large number of factors, however, that may influence community development. One such factor is colour. The hypothesis was that differences in colour may impact the short-term development of a biofouling community and therefore bias the results. An experiment was designed to investigate the effect of black and white substrata on settlement of fouling organisms in the field. Both Ulva sp. and Spirorbis sp. had significantly higher settlement on black surfaces. This result emphasises the importance of considering colour and other factors when undertaking short-term testing of AF coatings.     

Evaluation of dihydrooroidin as an antifouling additive in marine paint

Methods used to deter biofouling of underwater structures and marine vessels present a serious environmental issue and are both problematic and costly for government and commercial marine vessels worldwide. Current antifouling methods include compounds that are toxic to aquatic wildlife and marine ecosystems. Dihydrooroidin (DHO) was shown to completely inhibit Halomonas pacifica biofilms at 100 μM in a static biofilm inhibition assay giving precedence for the inhibition of other marine biofilm-forming organisms. Herein we present DHO as an effective paint-based, non-cytotoxic, antifouling agent against marine biofouling processes in a marine mesocosm.     

Doubly biomimetic catecholic phosphorylcholine copolymer: a platform strategy for fabricating antifouling surfaces

A doubly biomimetic PMNC polymer bearing cell antifouling phosphorylcholine and mussel adhesive protein catechol groups is synthesized. The polymer can be deposited onto a variety of substrates by dip-coating in an aqueous solution, adhering to surfaces via the catechol functional group while at the same time forming a cell outer membrane mimetic antifouling surface. Contact angle, ATR-FTIR and XPS measurements confirm polymer coating formation on a variety of inorganic and organic substrates. BSA and bovine plasma fibrinogen protein adsorption on PMNC coated surfaces are reduced significantly compared to unmodified substrates, and platelet adhesion from human serum onto the PMNC coated substrate surfaces is highly suppressed in this study.     

The potential efficacy and application of freshwater and hypersaline immersion to control the spread of a marine invasive species

Introduced into New Zealand waters in 2008, the polychaete worm Sabella spallanzanii (Gmelin, 1791) is a marine invasive species with potential for significant ecological and economic impact. Within New Zealand, efforts to cope with this pest have focused on containment as efficacious control methods are in their infancy. To remedy this, we tested the efficacy of hyper-saline (50‰) and hypo-saline (0‰) baths as a potential control method for this species. Specimens of S. spallanzanii were collected from within the Auckland region and exposed to salinity treatments for up to 1440 min (24 h) and mortality rates were compared using LT₅₀ i.e. number of minutes taken for 50% of worms to die. Specimens subjected to hypo-saline conditions resulted in an LT₅₀ of 31.0 min compared to 132.0 min for hyper-saline conditions. Accordingly, hypo-saline dips have potential as an environmentally safe and cost-effective management method for maintenance of recreational vessels and other marine structures (e.g. aquaculture gear and shellfish stocks) that are heavily fouled with S. spallanzanii.     

Presence and effects of marine microbial biofilms on biocide-based antifouling paints

Marine microorganisms are capable of successfully colonizing toxic surfaces through the formation of biofilm structures. In this article, most of the literature reporting the presence of marine biofilms on chemically-active antifouling paints is briefly reviewed. Of special concern is the influence of the dense extracellular polymeric substances (EPS) matrix on the release rate of the compounds involved in antifouling paint performance (i.e. active compounds and controlled-release binder molecules). A deeper understanding of these phenomena is of interest for both environmental legislators and paint formulators.     

Presence and effects of marine microbial biofilms on biocide-based antifouling paints

Abstract

Marine microorganisms are capable of successfully colonizing toxic surfaces through the formation of biofilm structures. In this article, most of the literature reporting the presence of marine biofilms on chemically-active antifouling paints is briefly reviewed. Of special concern is the influence of the dense extracellular polymeric substances (EPS) matrix on the release rate of the compounds involved in antifouling paint performance (i.e. active compounds and controlled-release binder molecules). A deeper understanding of these phenomena is of interest for both environmental legislators and paint formulators.     

The performance of hybrid titania/silica-derived xerogels as active antifouling/fouling-release surfaces against the marine alga Ulva linza: in situ generation of hypohalous acids

Mixed titania/silica xerogels were prepared using titanium tetraisopropoxide (TTIP) and tetraethoxy orthosilicate (TEOS). Xerogel properties were modified by incorporating n-octyltriethoxysilane (C8). The xerogels catalyze the oxidation of bromide and chloride with hydrogen peroxide (H₂O₂) to produce hypohalous acids at pH 7 and pH 8. The antifouling/ fouling-release performance of a TTIP/C8/TEOS xerogel in the presence and absence of H₂O₂ was evaluated for the settlement of zoospores of the marine alga Ulva linza and for the removal of sporelings (young plants). In the absence of H₂O₂, differences in the settlement of zoospores and removal of sporelings were not significant relative to a titanium-free C8/TEOS xerogel. Addition of H₂O₂ gave a significant reduction in zoospore settlement and sporeling removal relative to the C8/TEOS xerogel and relative to peroxide-free conditions. The impact of TTIP on xerogel characteristics was evaluated by comprehensive contact angle analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy.     

The symbiotic role of marine microbes on living surfaces

Every surface immersed in the sea rapidly becomes covered with a biofilm. On inanimate surfaces, this is often followed by colonisation by larger organisms, and general macrofouling. On the other hand, the majority of marine organisms remain relatively free from macrofouling, although some may be covered in a thin film of epibiotic bacteria. The role of these bacteria in maintaining the health of the host has received little attention. Here we describe an ecological role for epibiotic bacteria from seaweed surfaces. These epibionts may play a protective role, releasing compounds into the surrounding seawater that help prevent extensive fouling of the surface. These compounds may also have industrial and medical applications. The relative ease of culturing these microbes, compared to other bacteria that produce active compounds suggests seaweed-associated bacteria may be useful in bioprocess applications, such as the production of antimicrobial or antifouling compounds.     

Effects of small-scale disturbance on invasion success in marine communities

Introductions of non-indigenous species have resulted in many ecological problems including the reduction of biodiversity, decline of commercially important species and alteration of ecosystems. The link between disturbance and invasion potential has rarely been studied in the marine environment where dominance hierarchies, dynamics of larval supply, and resource acquisition may differ greatly from terrestrial systems. In this study, hard substrate marine communities in Long Island Sound, USA were used to assess the effect of disturbance on resident species and recent invaders, ascidian growth form (i.e. colonial and solitary growth form), and the dominant species-specific responses within the community. Community age was an additional factor considered through manipulation of 5-wk old assemblages and 1-yr old assemblages. Disturbance treatments, exposing primary substrate, were characterized by frequency (single, biweekly, monthly) and magnitude (20%, 48%, 80%) of disturbance. In communities of different ages, disturbance frequency had a significant positive effect on space occupation of recent invaders and a significant negative effect on resident species. In the 5-wk community, magnitude of disturbance also had a significant effect. Disturbance also had a significant effect on ascidian growth form; colonial species occupied more primary space than controls in response to increased disturbance frequency and magnitude. In contrast, solitary species occupied significantly less space than controls. Species-specific responses were similar regardless of community age. The non-native colonial ascidian Diplosoma listerianum responded positively to increased disturbance frequency and magnitude, and occupied more primary space in treatments than in controls. The resident solitary ascidian Molgula manhattensis responded negatively to increased disturbance frequency and magnitude, and occupied less primary space in treatments than in controls. Small-scale biological disturbances, by creating space, may facilitate the success of invasive species and colonial organisms in the development of subtidal hard substrate communities.