Bacterial Fouling Research Articles

Lipophilic Defenses From Alcyonium Soft Corals of Antarctica

Alcyonacean soft corals lack physical or skeletal defenses and their nematocyst system is weak, leading to the conclusion that soft corals mainly rely on chemistry for protection from predators and microbes. Defensive chemicals of primary and secondary metabolic origin are exuded in the mucus surface layer, explaining the general lack of heavy fouling and predation in corals. In Antarctic ecosystems, where generalist predation is intense and mainly driven by invertebrate consumers, the genus Alcyonium is represented by eight species. Our goal was to investigate the understudied chemical ecology of Antarctic Alcyonium soft corals. We obtained six samples belonging to five species: A. antarcticum, A. grandis, A. haddoni, A. paucilobulatum, and A. roseum, and assessed the lipid-soluble fractions for the presence of defensive agents in these specimens. Ethyl ether extracts were tested in feeding bioassays with the sea star Odontaster validus and the amphipod Cheirimedon femoratus as putative sympatric predators. Repellent activities were observed towards both consumers in all but one of the samples assessed. Moreover, three of the extracts caused inhibition to a sympatric marine bacterium. The ether extracts afforded characteristic illudalane sesquiterpenoids in two of the samples, as well as particular wax esters subfractions in all the colonies analyzed. Both kinds of metabolites displayed significant deterrent activities demonstrating their likely defensive role. These results suggest that lipophilic chemicals are a first line protection strategy in Antarctic Alcyonium soft corals against predation and bacterial fouling.

Study on a novel nanofiltration membrane prepared by interfacial polymerization with zwitterionic amine monomers

A novel zwitterionic amide monomer (N-aminoethyl piperazine propane sulfonate, AEPPS) was synthesized and utilized in conjunction with piperazine (PIP) to perform the interfacial polymerization with trimesoyl chloride (TMC), producing thin-film composite (TFC) nanofiltration membranes (NFMs) with improved separation performance and antifouling property. Chemical structures and compositions of the zwitterionic monomers AEPPS and NFMs were characterized by (attenuated total reflectance) fourier transform infrared spectroscopy, nuclear magnetic resonance spectrometer and X-ray photoelectron spectroscopy. The surface morphology and hydrophilicity of NFMs were examined by field emission scanning electron microscopy, atomic force microscopy, dynamic water contact angle. The water permeability and antifouling property of NFMs are improved via introducing AEPPS into membranes. When tested with 1gL−1 K2SO4 aqueous solution at 25°C and 0.6MPa, the water flux of NFMs increases from 23.4Lm−2h−1 to 43.1Lm−2h−1 with increasing AEPPS content from 0mol% to 3.2mol%, while K2SO4 rejection maintains around 97%. The NFMs containing zwitterionic moieties can resist bacterial adsorption and protein fouling efficiently, and show a stable and good separation performance during a long-time filtration process of 288h.

Temperature effects on larval survival, larval period, and health of hatchery-reared red king crab, Paralithodes camtschaticus

We tested the effects of two rearing temperatures (8 and 11°C) on survival, larval period, and health of red king crab (Paralithodes camtschaticus) larvae in eight hatchery-scale 1200L tanks as part of a stock enhancement feasibility study. Larvae were stocked at a density of 50larvaeL−1. Survival did not vary from the newly hatched first stage zoea to the glaucothoe and first juvenile crab stage (C1) between the two temperatures. Survival averaged 50% from stocking to the glaucothoe stage and 20% from stocking to C1. Overall, 480,000 Z1s were stocked and 96,200 C1s were produced. Larval periods were significantly shorter at the higher temperature, averaging 21days from stocking to glaucothoe and 35days from stocking to C1 at 11°C compared to 30days to glaucothoe and 50days to C1 at 8°C. Specific attributes of larval health measured in this study included the size and relative number of lipid droplets in the anterior region of the larval gut as a measure of stored energy reserves and percentage of the surface of the larval exoskeleton fouled with filamentous bacteria. Quantitative assessment of accumulated lipids as measured by maximum lipid droplet diameters and relative numbers of lipid droplets in the anterior region of the gut was not significantly different between larvae reared at the two temperatures, suggesting that larvae were able to accumulate similar quantities of lipid energy reserves at both temperatures. Filamentous bacterial fouling was greater during the late Z4 stage in the larvae reared at 8°C compared to those reared at 11°C, which was likely due to the longer intermolt duration at the lower temperature allowing more time for bacterial accumulation on the exoskeleton. We found that red king crab larvae can be cultured in a substantially shorter time period without compromising survival or health by increasing rearing temperature from 8 to 11°C.

Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N′-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2 h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24 h exposure) and cyprid settlement (24 and 48 h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.

Layer-by-Layer Click Deposition of Functional Polymer Coatings for Combating Marine Biofouling

"Click" chemistry-enabled layer-by-layer (LBL) deposition of multilayer functional polymer coatings provides an alternative approach to combating biofouling. Fouling-resistant azido-functionalized poly(ethylene glycol) methyl ether methacrylate-based polymer chains (azido-poly(PEGMA)) and antimicrobial alkynyl-functionalized 2-(methacryloyloxy)ethyl trimethyl ammonium chloride-based polymer chains (alkynyl-poly(META)) were click-assembled layer-by-layer via alkyne-azide 1,3-dipolar cycloaddition. The polymer multilayer coatings are resistant to bacterial adhesion and are bactericidal to marine Gram-negative Pseudomonas sp. NCIMB 2021 bacteria. Settlement of barnacle ( Amphibalanus (= Balanus ) amphitrite ) cyprids is greatly reduced on the multilayer polymer-functionalized substrates. As the number of the polymer layers increases, efficacy against bacterial fouling and settlement of barnacle cyprids increases. The LBL-functionalized surfaces exhibit low toxicity toward the barnacle cyprids and are stable upon prolonged exposure to seawater. LBL click deposition is thus an effective and potentially environmentally benign way to prepare antifouling coatings.

Polyelectrolyte and Silver Nanoparticle Modification of Microfiltration Membranes To Mitigate Organic and Bacterial Fouling

Membrane fouling remains one of the most problematic issues surrounding membrane use in water and wastewater treatment applications. Organic and biological fouling contribute to irreversible fouling and flux decline in these processes. The aim of this study was to reduce both organic and biological fouling by modifying the surface of commercially available poly(ether sulfone) (PES) membranes using the polyelectrolyte multilayer modification method with poly(styrenesulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), and silver nanoparticles (nanoAg) integrated onto the surface as stable, thin (15 nm) films. PSS increases the hydrophilicity of the membrane and increases the negative surface charge, while integration of nanoAg into the top PSS layer imparts biocidal characteristics to the modified surface. Fouling was simulated by filtering aqueous solutions of humic acid (5 and 20 mg L(-1)), a suspension of Escherichia coli (10(6) colony-forming units (CFU) mL(-1)), and a mixture of both foulants through unmodified and modified PES membranes under batch conditions. Filtration and cleaning studies confirmed that the modification significantly reduced organic and biological fouling.

Non-leaching antimicrobial surfaces through polydopamine bio-inspired coating of quaternary ammonium salts or an ultrashort antimicrobial lipopeptide

Bacterial fouling on surfaces significantly increases the resistance of bacteria toward antibiotics, which leads to medical complications and a corresponding financial burden. Here, we report on a general and robust technique for facile modification of various surfaces with different antibacterial agents. Our approach in this study was inspired by the strong adhesion of mussel adhesion proteins (MAPs) to many types of surfaces, including metals, polymers, and inorganic materials. Thus, glass and polymeric slides were dip-coated with dopamine, as a MAP mimic, and the resulting surfaces were characterized. The reactivity of dopamine-coated surfaces toward nucleophilic addition was then confirmed by reacting them with fluorescent probes containing either a free amino or a free thiol group. Laser scanning confocal microscopy (LSCM), X-ray photoelectron spectroscopy (XPS), confocal Raman microscopy, matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectroscopy, and cyclic voltammetry studies collectively suggested that the probes had covalently attached to the surfaces. Fabrication of dopamine-coated surfaces with an antibacterial quaternary amine or an ultrashort lipopeptide analog generated surfaces that effectively kill Escherichia coli and Staphylococcus aureuscells on contact. Moreover, minimal leaching of the fabricated agent was detected after prolonged incubation. This technique could be further developed to a “paint-like” or self-assembling monolayer-like procedure for the preparation of antibacterial surfaces on various materials.

Colloidal and bacterial fouling during constant flux microfiltration: Comparison of classical blocking laws with a unified model combining pore blocking and EPS secretion

The instantaneous transmembrane pressure needs to be continuously increased to compensate for foulant accumulation during constant flux microfiltration. Herein, we compare predictions of a unified mathematical model and conventional blocking laws with laboratory data obtained during constant flux operation. Foulants employed included single species cultures of bacteria and coagulated natural colloids, both of which are known to form compressible cakes. The first principles model unifies fouling arising from pore blocking by individual cells, cake formation, as well as bacterial secretion of exopolymers. It also incorporates non-uniform spatial deposition patterns that have been observed during unstirred dead-end filtration. Mechanistically, these heterogeneities arise either from non-uniform membrane surface porosity or stochastic initial binding of foulants. Previous studies have shown that the initial patchy or uneven deposit morphology is magnified over longer time-scales during bacterial filtration by differential extracellular polymeric substances (EPS) secretion through quorum sensing. However, in this study, we are primarily interested in the averaged behavior (mainly flux and pressure). By spatially averaging the microscale variables we are able to compare with classical blocking law models. We show that blocking laws and the unified model both accurately model fouling under our experimental conditions. The unified model provides mechanistic insights into (bio)colloid deposition and associated fouling during constant flux microfiltration particularly since it is obtained excellent predictive agreement with experimental data using parameters taken exclusively from our recent study of constant pressure filtration.

Physical–chemical properties, separation performance, and fouling resistance of mixed-matrix ultrafiltration membranes

Herein we report on the formation and characterization of mixed-matrix ultrafiltration (UF) membranes hand-cast by nonsolvent induced phase inversion. We evaluated nanometer-to-micrometer sized inorganic fillers (silver, copper, silica, zeolite, and silver-zeolite) materials with polysulfone (PSf) as the polymeric dispersing matrix. In general, mixed-matrix membranes were rougher, more hydrophilic, and more mechanically robust. Only sub-micron zeolite-PSf mixed-matrix membranes exhibited simultaneous improvements in water permeability and solute selectivity; all other mixed-matrix membranes were more permeable, but less selective due to defects associated with poor polymer-filler binding. Protein and bacterial fouling resistance of mixed-matrix membranes containing silver, zeolite, and silver-zeolite nanoparticles were compared to a low-fouling, poly(acrylonitrile) (PAN) UF membrane. Zeolite and silver containing membranes exhibited better protein fouling resistance (due to higher hydrophilicity), whereas silver and silver-zeolite based membranes produce better bacterial fouling resistance due to antimicrobial properties. Overall, zeolite-PSf and silver exchanged zeolite-PSf membranes offered the best combination of improved permeability, selectivity, and fouling resistance — superior to the commercial PAN membrane.

Chemical defense against predators and bacterial fouling in the Mediterranean sponges Axinella polypoides and A. verrucosa

Chemical defense against predators and bacterial fouling in the Mediterranean sponges Axinella polypoides and A. verrucosa

Induction of halogenated vesicle transport in cells of the red seaweed Laurencia obtusa

In clones of the red alga Laurencia obtusa, the frequency of vesicle transport from corps en cerise (CC) to the cell wall region was evaluated in response to differences in temperature, irradiance, desiccation, bacterial fouling, and bromine (Br) availability. In addition, the morphology of the corps en cerise was analyzed. Traffic of vesicles was induced by exposing L. obtusa to low temperatures and variations in irradiance. It was also verified that bacterial fouling induced vesicle traffic. Under high temperatures and desiccation, the membranous tubular connections were lost and transport of vesicles was not seen. The morphology of the corps en cerise varied according to the availability of Br in seawater. Exocytosis of secondary metabolites by L. obtusa was shown to vary in relation to temperature, irradiance, desiccation and bacterial fouling. The data suggest that the transport of vesicles in L. obtusa may be related to the inhibition of the microfouling community on the algal surface.

Incorporating pore blocking, cake filtration, and EPS production in a model for constant pressure bacterial fouling during dead-end microfiltration

Microfiltration is used in a wide range of municipal and industrial settings to remove particulate matter including pathogenic microorganisms such as bacteria and protozoa. As more water is filtered at constant pressure, the accumulation of retained particles on the membrane decreases the filtration rate; a process commonly referred to as fouling. Mathematical treatment of flux decline has proved to be a useful tool in diagnosing filtration data even though the mathematical underpinnings are not completely understood. In particular, little is known about the transition between fouling phenomena (e.g. pore blocking to cake filtration). Moreover, less is known about the effect of extracellular polymeric substances (EPS) production by bacteria when they accumulate on a membrane over extended durations. In this manuscript, we develop a novel approach to model bacterial microfiltration by considering the effects of both differential binding and exopolymer production. Spatial gradients in bacteria concentrations initially occur due to the non-uniform membrane surface porosity and differential deposition caused by the stochastic nature of microorganism adhesion. These heterogeneities in bacterial deposition and associated pore blocking result in variable secretion of extracellular polymers. Long-term fouling is quantified as the cumulative resistance posed by both bound bacteria and EPS. We compare numerical simulations quantitatively and qualitatively to previously published experimental data and investigate variations of microbial deposition patterns across the membrane. We find substantial agreement between the model and experimental observations. We are also able to conclude that fluid dynamics must be important if the dominant variability is in the membrane structure, rather than in bacterial adhesion. However, variation in bacterial adhesion alone can also induce substantial spatial heterogeneity.

Development of the primary bacterial microfouling layer on antifouling and fouling release coatings in temperate and tropical environments in Eastern Australia

The role played by bacteria during the pioneering stages of colonisation on marine coatings was investigated over three distinct seasons in both tropical and temperate environments. Novel methods were developed to facilitate the study of the adhered bacterial population on the test coatings in their native, hydrated state. The approach eliminated destructive sample preparation techniques, including sample dehydration and/or removal from the substratum surface prior to analysis. Bacterial colonisation during initial biofilm formation was evaluated on two antifouling paints, Intersmooth 360® and Super Yacht 800®, and a fouling release coating, Intersleek 700®. Bacterial colonisation was quantified on all three coating surfaces. Intersleek 700 displayed the quickest colonisation by bacteria, resulting in major modification of the substratum surface within 2–4 days following immersion in the ocean. Whilst fouling accumulated more quickly on Intersleek 700, by 16 days all three coatings were fouled significantly. Bacterial fouling was correlated to both location and season, with fouling occurring at a more rapid rate at the Cairns location, as well as during the summer months, when higher water temperatures were recorded. Successful colonisation of all coatings by bacteria soon after immersion modifies the characteristics of the surfaces at the hull/water interface, and subsequent settlement by higher biofouling organisms must be moderated by these modified surfaces.

Regularized Stokeslets solution for 2-D flow in dead-end microfiltration: Application to bacterial deposition and fouling

Dead-end microfiltration is an effective method for removing particulate matter including protozoa and bacteria in a variety of settings. As the filtered components accumulate on the filter, the flux declines during constant pressure operation necessitating periodic back-washing. It has been recently reported empirically that the filtered components are not homogeneously distributed on the filter. This must be accounted for in any mathematical theory describing the filtering process. We present a method for determining the coupled fluid dynamics and bacterial transport for dead-end filtration. Results of numerical simulation indicate that the model is able to closely capture experimental data; moreover, the model predicts that the coupled system induces the experimentally observed patchy deposition patterns through spatial variability in the pore structure and porosity of the membrane.

Protein, cell and bacterial fouling resistance of polypeptoid-modified surfaces: effect of side-chain chemistry.

Peptidomimetic polymers consisting of poly-N-substituted glycine oligomers (polypeptoids) conjugated to biomimetic adhesive polypeptides were investigated as antifouling surface coatings. The polymers were immobilized onto TiO(2) surfaces via an anchoring peptide consisting of alternating residues of 3,4-dihydroxyphenylalanine (DOPA) and lysine. Three polypeptoid side-chain compositions were investigated for antifouling performance and stability toward enzymatic degradation. Ellipsometry and XPS analysis confirmed that purified polymers adsorbed strongly to TiO(2) surfaces, and the immobilized polymers were resistant to enzymatic degradation as demonstrated by mass spectrometry. All polypeptoid-modified surfaces exhibited significant reductions in adsorption of lysozyme, fibrinogen and serum proteins, and were resistant to 3T3 fibroblast cell attachment for up to seven days. Long-term in vitro cell attachment studies conducted for six weeks revealed the importance of polypeptoid side-chain composition, with a methoxyethyl side chain providing superior long-term fouling resistance compared to hydroxyethyl and hydroxypropyl side chains. Finally, attachment of both gram-positive and gram-negative bacteria for up to four days under continuous-flow conditions was significantly reduced on the polypeptoid-modified surfaces compared to unmodified TiO(2) surfaces. The results reveal the influence of polypeptoid side-chain chemistry on short-term and long-term protein, cell and bacterial fouling resistance.

Active substances from Ceramium botryocarpum used as antifouling products in aquaculture

Epiphytes and fouling organisms induce problems in aquaculture, reducing yield of open-water and on-shore farms. By weighing down materials, fouling can also cause equipment failure. The presence of Ceramium botryocarpum (Rhodophyta, Ceramiales) in tank cultures (Innovalg, France) significantly limits the establishment of opportunist green algae such as Cladophora, Bryopsis or Ulva usually disturbing the cultures. In order to demonstrate the antifouling activity of substances released by C. botryocarpum, the activities of different extracts have been tested on representative marine species such as marine bacteria, phytoplankton, and spores of macroalgae. The extracts from spring strongly inhibit the development of marine bacteria, phytoplankton and spores of Ulva at concentrations between 25 and 150 μg mL − 1 . These results confirm the presence of active substances in C. botryocarpum. No significative trend on the variation in the antifouling activity from September to July has been highlighted. Compared with toxic biocides commonly used in antifouling paints, natural extracts of Ceramium present no cytotoxicity. Active substances from C. botryocarpum could be used to fight against bacterial and algal fouling problems in aquaculture systems.

ULTRASTRUCTURE OF THE GLAND CELLS OF THE RED ALGA ASPARAGOPSIS ARMATA (BONNEMAISONIACEAE)1

Localization of natural products in the gland cells of the tetrasporophyte of Asparagopsis armata Harvey was examined using light microscopy, epifluorescence microscopy, and TEM. A. armata produces a range of halogenated metabolites that deter herbivores and inhibit bacterial fouling. The halogenated metabolites accumulate as a refractile inclusion inside specialized gland cells and this inclusion was no longer produced when the alga was cultured without bromine. Gland cells are formed soon after the apical division and can occupy a large portion of the algal volume, up to 10% of some parts of the filament. TEM was carried out on cryofixed and freeze‐substituted samples. Ultrastructure studies revealed that gland cells are positioned inside the pericentral cell, originating from the axial cell wall. The refractile inclusion of these gland cells is comprised of numerous electron‐translucent vacuoles enclosed by an electron‐opaque matrix. Some contents of the inclusion autofluoresced under UV excitation by epifluorescence microscopy. Light microscopy further revealed that stalk‐like structures connected the gland cell to the outer wall of the pericentral cell. These stalk‐like structures may provide the mechanism for metabolite transfer to the algal surface. Gland cell walls are relatively thin, which in turn would aid the transfer of metabolites to the stalk‐like structure. These features of the gland cells provide essential clues to the production and storage of the halogenated metabolites in A. armata and offer new insights into a possible mechanism for their release.

Initial Stages of Bacterial Fouling during Dead-End Microfiltration

Constant pressure experiments were performed using track-etched polycarbonate membranes and rod-shaped bacteria (viz., Brevundimonas diminuta and Serratia marcescens) to study flux decline and backwashing during the early stages of microfiltration. The intermediate blocking law originally derived for spherical particles was modified to account for the approximate cylindrical shape of the selected bacteria. A deposition factor was introduced to empirically account for the morphology of bacterial deposits. The initial stages of flux decline prior to the secretion of new extracellular polymeric substances (EPS) was quantitatively described by the intermediate blocking law before transitioning to cake filtration at later times. Scanning electron microscopy (SEM) provided additional visual evidence that bacteria simultaneously deposited directly on the membrane and on each other during early stages of filtration as assumed bythe intermediate blocking law. Empirical deposition factors decreased with initial permeate flux indicating its effect on bacteria deposition patterns, which was also confirmed by SEM. Bacteria were easily removed following short filtration times before significant secretion of new EPS by simply rinsing with ultrapure water, thereby completely restoring the clean membrane permeability. In contrast, this rinsing procedure did not completely recover the membrane permeability following longer durations when significant amounts of new EPS proteins and polysaccharides were secreted. Consequently, backwashing effectiveness during water and wastewater microfiltration will be high prior to EPS production whereas flux recovery may not be possible solely by hydrodynamic means once EPS are secreted.

Superoxide production by marine microalgae

This study investigated the possible roles of superoxide produced by raphidophyte and prymnesiophyte microalgae as an ichthyotoxic agent to damselfish and an allelopathic agent to bacteria. We found that the rate of superoxide production varied with algal cell density, with cell densities of the raphidophyte Chattonella marina > 10,000 cells ml-1 producing less environmental levels of superoxide per cell (94 ± 14 chemiluminescence units) than cell densities < 10,000 cells ml-1 (390 ± 54 units per cell). Microalgal cells have the capacity to change their superoxide production rate over a period of 1 h, dependent on cell density and metabolic activity. We also examined the effect of superoxide on suppression of bioluminescence of the marine bacterium Vibrio fischeri as a model for bacterial alleopathy and found that both superoxide and free fatty acids such as eicosapentaenoic acid (EPA; 20:5ω3) present in raphidophyte microalgal cells cause suppression of bacterial bioluminescence. The combination of superoxide in the presence of EPA further enhanced bioluminescence suppression. Superoxide was also found to enhance the toxicity of free fatty acid EPA to damselfish (Acanthochromis polycanthus) at concentrations as low as 0.2 mg l-1. In conclusion, consideration should be given to density dependent and/or metabolic variations of toxicity when publishing minimum alert levels for superoxide producing ichthyotoxic microalgal species. A secondary role of superoxide production may be to enhance the toxicity of algal exudates or serve as an allelopathic agent against bacterial fouling. © Springer-Verlag 2005.

Chemical inhibition of bacterial colonization by the red alga Bonnemaisonia hamifera

Attachment and growth are 2 major processes in bacterial colonization of surfaces in the sea. By inhibiting either or both of these processes, marine macroorganisms may defend themselves against bacterial infection and fouling. We tested crude extracts from 5 red seaweed species for their ability to inhibit bacterial growth and attachment. For this we used 11 strains of bacteria, represent- ing 5 different taxonomic groups. The effects on growth and attachment were tested by a standard disc-diffusion assay and by incorporating crude extracts into phytagel blocks that served as a surface for bacterial attachment. Extracts from one of the tested algae, Bonnemaisonia hamifera, were partic- ularly active and inhibited growth of 9 bacteria at concentrations volumetrically equivalent to whole algal tissue, or lower. The other 4 algal extracts had weak growth-inhibiting effects on only a few bacterial strains. None of the algal extracts exhibited broad-spectrum effects against bacterial attach- ment, but 4 of 5 algal extracts had some strain-specific effects. Surface extracts of B. hamifera tested on bacteria showed that metabolites are naturally present at sufficiently high concentrations in order to inhibit bacterial growth on the surface of the seaweed. In situ quantification of bacteria on B. ham- ifera also showed that this alga had significantly fewer bacteria on its surface compared to a co- existing alga. These findings suggest that B. hamifera naturally reduces its epibacterial abundance by production of broad-spectrum growth-inhibiting secondary metabolites. This is one of a few examples where ecologically relevant effects of algal metabolites on bacterial colonization have been shown.