淡水入侵生物沼蛤的污损机制与防污措施研究进展

沼蛤是一种典型的淡水入侵贝类,能够利用其分泌的足丝牢固黏附在多种水下基质表面,引起严重的生物污损问题。沼蛤污损不但影响水生态系统健康,也给水利工程、交通运输、水产养殖等行业带来经济损失,已成为全球水生态系统安全和国民经济重要行业的潜在威胁,相关防污工作亟待开展。欲从根本上解决沼蛤污损问题,一方面需要加强对其基础生物学特性和污损机制的深入解析,另一方面也需要在此基础上研发更加经济、高效、环境友好的防污措施。本文综述了近年来国内外关于沼蛤污损生物学特性、污损机制和防污措施方面的研究进展,尤其是对沼蛤生物污损发生的主要机制如足探测识别、足丝黏附和环境影响等方面进行了总结,也从物理、化学、生物和防污材料等角度阐述了现有的沼蛤污损控制措施并对未来发展方向进行了展望,以期更加深入地理解沼蛤生物污损现象,为揭示其作用机制、制定科学有效的防污措施、维护水生态系统安全提供数据支撑,综述内容对于水下仿生材料研发也具有重要的参考价值。     

Application of atomic force microscopy to the study of micromechanical properties of biological materials

Atomic force microscopy (AFM) has been used to study the micromechanical properties of biological systems. Its unique ability to function both as an imaging device and force sensor with nanometer resolution in both gaseous and liquid environments has meant that AFM has provided unique insights into the mechanical behaviour of tissues, cells and single molecules. As a surface scanning device, AFM can map properties such as adhesion and the Young's modulus of surfaces. As a force sensor and nanoindentor AFM can directly measure properties such as the Young's modulus of surfaces or the binding forces of cells. As a stress-strain gauge AFM can study the stretching of single molecules or fibres and as a nanomanipulator it can dissect biological particles such as viruses or DNA strands. The present paper reviews key research that has demonstrated the versatility of AFM and how it can be exploited to study the micromechanical behaviour of biological materials.     

Fouling and its control in heat exchangers in the dairy industry

Fouling of heat transfer equipment poses a major problem in the food and especially the dairy industry. A review of recent progress made in the study and understanding of fouling and cleaning mechanisms in relation to exchangers and heat exchange surfaces in contact with milk components is given.

The first part describes the different materials and methods used in the study of fouling and cleaning, from laboratory to pilot‐plant and industrial scale.

The second part concerns the different fouling dynamics observed with milk and dairy products, and gives an interpretation of the different behaviours which occur, on the basis of the most recent results on the composition and structure of the deposits and the biochemical mechanisms of fouling.

The last part is a complete review of cleaning of milk deposits, taking into account the chemical reaction approach to cleaning as a mass transfer phenomenon.     

The potential for translocation of marine species via small-scale disruptions to antifouling surfaces

Vessel hull fouling is a major vector for the translocation of nonindigenous species (NIS). Antifouling (AF) paints are the primary method for preventing the establishment and translocation of fouling species. However, factors such as paint age, condition and method of application can all reduce the effectiveness of these coatings. Areas of hull that escape AF treatment (through limited application or damage) constitute key areas that may be expected to receive high levels of fouling. The investigation focused on whether small-scale (mm(2) to cm(2)) areas of unprotected surface or experimental 'scrapes' provided sufficient area for the formation of fouling assemblages within otherwise undamaged AF surfaces. Recruitment of fouling taxa such as algae, spirorbids and hydroids was recorded on scrapes as narrow as 0.5 cm wide. The abundance and species richness of fouling assemblages developing on scrapes > or =1 cm often equalled or surpassed levels observed in reference assemblages totally unprotected by AF coatings. Experiments were conducted at three sites within the highly protected and isolated marine park surrounding Lady Elliott Island at the southernmost tip of the Great Barrier Reef, Australia. Several NIS were recorded on scrapes of AF coated surfaces at this location, with 1-cm scrapes showing the greatest species richness and abundance of NIS relative to all other treatments (including controls) at two of the three sites investigated. Slight disruptions to newly antifouled surfaces may be all that is necessary for the establishment of fouling organisms and the translocation of a wide range of invasive taxa to otherwise highly protected marine areas.     

The potential for translocation of marine species via small-scale disruptions to antifouling surfaces

Vessel hull fouling is a major vector for the translocation of nonindigenous species (NIS). Antifouling (AF) paints are the primary method for preventing the establishment and translocation of fouling species. However, factors such as paint age, condition and method of application can all reduce the effectiveness of these coatings. Areas of hull that escape AF treatment (through limited application or damage) constitute key areas that may be expected to receive high levels of fouling. The investigation focused on whether small-scale (mm² to cm²) areas of unprotected surface or experimental ‘scrapes’ provided sufficient area for the formation of fouling assemblages within otherwise undamaged AF surfaces. Recruitment of fouling taxa such as algae, spirorbids and hydroids was recorded on scrapes as narrow as 0.5 cm wide. The abundance and species richness of fouling assemblages developing on scrapes ≥1 cm often equalled or surpassed levels observed in reference assemblages totally unprotected by AF coatings. Experiments were conducted at three sites within the highly protected and isolated marine park surrounding Lady Elliott Island at the southernmost tip of the Great Barrier Reef, Australia. Several NIS were recorded on scrapes of AF coated surfaces at this location, with 1-cm scrapes showing the greatest species richness and abundance of NIS relative to all other treatments (including controls) at two of the three sites investigated. Slight disruptions to newly antifouled surfaces may be all that is necessary for the establishment of fouling organisms and the translocation of a wide range of invasive taxa to otherwise highly protected marine areas.     

Attaching biological probes to silica optical biosensors using silane coupling agents

In order to interface with biological environments, biosensor platforms, such as the popular Biacore system (based on the Surface Plasmon Resonance (SPR) technique), make use of various surface modification techniques, that can, for example, prevent surface fouling, tune the hydrophobicity/hydrophilicity of the surface, adapt to a variety of electronic environments, and most frequently, induce specificity towards a target of interest. These techniques extend the functionality of otherwise highly sensitive biosensors to real-world applications in complex environments, such as blood, urine, and wastewater analysis. While commercial biosensing platforms, such as Biacore, have well-understood, standard techniques for performing such surface modifications, these techniques have not been translated in a standardized fashion to other label-free biosensing platforms, such as Whispering Gallery Mode (WGM) optical resonators. WGM optical resonators represent a promising technology for performing label-free detection of a wide variety of species at ultra-low concentrations. The high sensitivity of these platforms is a result of their unique geometric optics: WGM optical resonators confine circulating light at specific, integral resonance frequencies. Like the SPR platforms, the optical field is not totally confined to the sensor device, but evanesces; this "evanescent tail" can then interact with species in the surrounding environment. This interaction causes the effective refractive index of the optical field to change, resulting in a slight, but detectable, shift in the resonance frequency of the device. Because the optical field circulates, it can interact many times with the environment, resulting in an inherent amplification of the signal, and very high sensitivities to minor changes in the environment. To perform targeted detection in complex environments, these platforms must be paired with a probe molecule (usually one half of a binding pair, e.g. antibodies/antigens) through surface modification. Although WGM optical resonators can be fabricated in several geometries from a variety of material systems, the silica microsphere is the most common. These microspheres are generally fabricated on the end of an optical fiber, which provides a "stem" by which the microspheres can be handled during functionalization and detection experiments. Silica surface chemistries may be applied to attach probe molecules to their surfaces; however, traditional techniques generated for planar substrates are often not adequate for these three-dimensional structures, as any changes to the surface of the microspheres (dust, contamination, surface defects, and uneven coatings) can have severe, negative consequences on their detection capabilities. Here, we demonstrate a facile approach for the surface functionalization of silica microsphere WGM optical resonators using silane coupling agents to bridge the inorganic surface and the biological environment, by attaching biotin to the silica surface. Although we use silica microsphere WGM resonators as the sensor system in this report, the protocols are general and can be used to functionalize the surface of any silica device with biotin.     

Microbe-surface interactions in biofouling and biocorrosion processes.

The presence of microorganisms on material surfaces can have a profound effect on materials performance. Surface-associated microbial growth, i.e. a biofilm, is known to instigate biofouling. The presence of biofilms may promote interfacial physico-chemical reactions that are not favored under abiotic conditions. In the case of metallic materials, undesirable changes in material properties due to a biofilm (or a biofouling layer) are referred to as biocorrosion or microbially influenced corrosion (MIC). Biofouling and biocorrosion occur in aquatic and terrestrial habitats varying in nutrient content, temperature, pressure and pH. Interfacial chemistry in such systems reflects a wide variety of physiological activities carried out by diverse microbial populations thriving within biofilms. Biocorrosion can be viewed as a consequence of coupled biological and abiotic electron-transfer reactions, i.e. redox reactions of metals, enabled by microbial ecology. Microbially produced extracellular polymeric substances (EPS), which comprise different macromolecules, mediate initial cell adhesion to the material surface and constitute a biofilm matrix. Despite their unquestionable importance in biofilm development, the extent to which EPS contribute to biocorrosion is not well-understood. This review offers a current perspective on material/microbe interactions pertinent to biocorrosion and biofouling, with EPS as a focal point, while emphasizing the role atomic force spectroscopy and mass spectrometry techniques can play in elucidating such interactions.     

Interactions between cathodic protection and bacterial settlement on steel in seawater

Cathodic protection (CP) is a widely utilised method of corrosion prevention in aqueous systems. There is evidence that the electrochemical changes it produces on a metal surface influence the chemistry of the water and the settlement of fouling organisms. The interaction is in both directions, and fouling organisms and their products have an influence on the CP and on calcareous deposits formed on the metal in marine environments. The studies described show that on both stainless and nonstainless steels, CP retards the development of aerobic bacterial fouling. Increasing the CP decreases the number of bacteria. Additionally, the presence of organic material affects both the current required to maintain CP and the nature of the calcareous deposits formed. The results are discussed in relation to the electrochemistry of the system.     

A novel fluorescence-based array biosensor: principle and application to DNA hybridization assays

A novel fluorescence-based array biosensor targeted for field applications, such as environmental monitoring, has been developed, and successfully applied to DNA hybridization assays. The purpose was to meet the demand for automated, portable but easy-to-maintain systems allowing continuous flow monitoring of surface reactions. The biosensor presented here can be distinguished from the existing systems by the optical method used, which provides an enhanced simplicity and robustness, and enables a simple maintenance by potentially unskilled personnel. The system is based on a conventional microscope slide which acts both as transducer and biological array sensor. The excited fluorescence is guided by total internal reflection into the slide to the detector which is directly interfaced to the slide. Each region of the sensor array is successively optically interrogated, and the detection of the corresponding fluorescent emission synchronized. A real-time three-analyte analysis is thus feasible without any mechanical scanning movement or optical imaging systems as generally used in the existing instruments. The ability of the biosensor to operate in continuous flow for several tens of hours has been demonstrated. The biosensor has been assessed in terms of stability, and slide-to-slide reproducibility, which is found to be less than 3.7%, thus far below the standard biological reproducibility. DNA hybridization assays were performed to estimate a limit of detection, which was found to be 16 mol/microm(2), and to determine the reaction kinetics associated to the DNA model used. The developed biosensor is thus shown to be able to predict reaction kinetics, and to monitor in real time surface reactions between targets and probes.     

A Method for Molecular Dynamics on Curved Surfaces

Dynamics simulations of constrained particles can greatly aid in understanding the temporal and spatial evolution of biological processes such as lateral transport along membranes and self-assembly of viruses. Most theoretical efforts in the field of diffusive transport have focused on solving the diffusion equation on curved surfaces, for which it is not tractable to incorporate particle interactions even though these play a crucial role in crowded systems. We show here that it is possible to take such interactions into account by combining standard constraint algorithms with the classical velocity Verlet scheme to perform molecular dynamics simulations of particles constrained to an arbitrarily curved surface. Furthermore, unlike Brownian dynamics schemes in local coordinates, our method is based on Cartesian coordinates, allowing for the reuse of many other standard tools without modifications, including parallelization through domain decomposition. We show that by applying the schemes to the Langevin equation for various surfaces, we obtain confined Brownian motion, which has direct applications to many biological and physical problems. Finally we present two practical examples that highlight the applicability of the method: 1) the influence of crowding and shape on the lateral diffusion of proteins in curved membranes; and 2) the self-assembly of a coarse-grained virus capsid protein model.     

Mini review: Biomimetic models and bioinspired surfaces for fouling control

Nature provides many examples of mechanisms to control fouling. These defences can be copied (biomimetic) or tailored (bioinspired) to solve problems of fouling on manmade structures. With increasing research in this area over the last two decades, it is timely to review this burgeoning subject, in particular as the biofouling field shifts focus towards novel, physical mechanisms to prevent and control fouling. This change is being promoted by advances in nano- and micro-scale patterning as well as in a variety of nano-biotechnologies, which are transforming the translation of natural surfaces into experimental materials. In this article, research on the defence of marine organisms against fouling and the technologies they are defining is reviewed.     

Impact of wastewater fouling on contact angle

Capillary dependent systems are highly influenced by surface fouling and may degrade as material surface properties change. In anticipation of a spacecraft microgravity fluids management system exposed to highly variable wetting conditions, the impact of urine wastewater fouling on capillary contact angle was examined. The results indicate that, in general, surface fouling can decrease the contact angle when crystalline structures or biofilms form. Small crystalline growth on the order of 10 μm can lower advancing contact angles θ_adv by approximately 30°, while biofilm growth can lower it by approximately 15°. Vacuum drying of fouled surfaces increased θ_adv by about 8°, and defects greater in height than 5% of the capillary length increased θ_adv by approximately 30°. These trends may indicate that promotion of wastewater fouling may improve the performance of capillary dependent fluids management systems. These results may also influence terrestrial technologies, including medical catheters and sustainable wastewater treatment systems exposed to wastewater fouling.     

Identification of Thiothrix unzii in two distinct ecosystems

AIMS: Molecular procedures were used to identify Thiothrix spp. in biofilms from sulphide-rich waters in two distinct ecosystems. METHODS AND RESULTS: Biofilm samples were obtained from two groundwater-fed systems in central and northern Florida, including an artesian spring and municipal water tank. The 16S rDNA in each sample was directly amplified by polymerase chain reaction. CONCLUSIONS: Clonal libraries of biofilm 16S rDNA from each site contained rDNA sequences that were 99-99.5% similar to Thiothrix unzii. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of T. unzii in a natural system. Biofilm formation by Thiothrix spp. can cause fouling in groundwater processing equipment, including municipal water-processing facilities, agricultural irrigation systems and spring water bottling plant filters. Biofouling can have severe economic and human health impacts as it will influence flow rates and related water treatments. Characterization of specific fouling bacteria and their molecular ecology is essential for their regulation.     

Biological nitrogen and phosphorus removal in membrane bioreactors: model development and parameter estimation

Membrane bioreactors (MBR) are being increasingly used for wastewater treatment. Mathematical modeling of MBR systems plays a key role in order to better explain their characteristics. Several MBR models have been presented in the literature focusing on different aspects: biological models, models which include soluble microbial products (SMP), physical models able to describe the membrane fouling and integrated models which couple the SMP models with the physical models. However, only a few integrated models have been developed which take into account the relationships between membrane fouling and biological processes. With respect to biological phosphorus removal in MBR systems, due to the complexity of the process, practical use of the models is still limited. There is a vast knowledge (and consequently vast amount of data) on nutrient removal for conventional-activated sludge systems but only limited information on phosphorus removal for MBRs. Calibration of these complex integrated models still remains the main bottleneck to their employment. The paper presents an integrated mathematical model able to simultaneously describe biological phosphorus removal, SMP formation/degradation and physical processes which also include the removal of organic matter. The model has been calibrated with data collected in a UCT-MBR pilot plant, located at the Palermo wastewater treatment plant, applying a modified version of a recently developed calibration protocol. The calibrated model provides acceptable correspondence with experimental data and can be considered a useful tool for MBR design and operation.     

Effect of membrane morphology on system capacity during normal flow microfiltration

Understanding the effects of membrane fouling on system capacity is critical for the successful design and scale-up of microfiltration systems. The underlying morphology and structure of the microfiltration membrane can have a significant effect on system capacity by altering the rate and extent of fouling. Experimental data were obtained for system capacity during protein microfiltration using several model membranes with both homogeneous and composite structures. Data were compared with predictions of a new model that can account for both pore blockage and cake formation, and also includes the effects of membrane morphology on internal flow profiles within the membrane. Membranes with highly interconnected pores have a significantly higher capacity due to the reduction in flux decline arising from the fluid flow under and around any surface blockage. The model calculations are in good agreement with the flux decline data, allowing far more accurate predictions of system capacity than for the commonly used V(max) analysis.     

Fouling deterrence on the bivalve shell Mytilus galloprovincialis: a physical phenomenon?

The physical nature of fouling deterrence by the mussel Mytilus galloprovincialis was investigated using high-resolution biomimics of the bivalve surface. The homogeneous microtextured surface of M. galloprovincialis (1.94 +/- 0.03 microm), the smooth surface of the bivalve Amusium balloti (0 microm), and moulds of these surfaces (biomimics) were compared with controls of smooth (0 microm) and sanded moulds, (55.4 +/- 2.7 microm) and PVC strips (0 microm) in a 12-week field trial. The shell and mould of M. galloprovincialis were fouled by significantly fewer species and had significantly less total fouling cover than the shell and mould of A. balloti over a 12-week period. However, the major effects were between surfaces with and without microtopography. Surface microtopography, be it structured as in the case of M. galloprovincialis shell and mould, or random as in the case of the sanded mould, had a lower cover of fouling organisms than treatments without microtopography after 6 weeks. There was also no difference between the effect of the M. galloprovincialis mould and the sanded mould. The strong fouling deterrent effects of both these surfaces diminished rapidly after 6 to 8 weeks while that of M. galloprovincialis shell remained intact for the duration of the experiment suggesting factors in addition to surface microtopography contribute to fouling deterrence.     

Economic analysis as a basis for large-scale nitrogen control decisions: reducing nitrogen loads to the Gulf of Mexico

Economic analysis can be a guide to determining the level of actions taken to reduce nitrogen (N) losses and reduce environmental risk in a cost-effective manner while also allowing consideration of relative costs of controls to various groups. The biophysical science of N control, especially from nonpoint sources such as agriculture, is not certain. Widespread precise data do not exist for a river basin (or often even for a watershed) that couples management practices and other actions to reduce nonpoint N losses with specific delivery from the basin. The causal relationships are clouded by other factors influencing N flows, such as weather, temperature, and soil characteristics. Even when the science is certain, economic analysis has its own sets of uncertainties and simplifying economic assumptions. The economic analysis of the National Hypoxia Assessment provides an example of economic analysis based on less than complete scientific information that can still provide guidance to policy makers about the economic consequences of alternative approaches. One critical value to policy makers comes from bounding the economic magnitude of the consequences of alternative actions. Another value is the identification of impacts outside the sphere of initial concerns. Such analysis can successfully assess relative impacts of different degrees of control of N losses within the basin as well as outside the basin. It can demonstrate the extent to which costs of control of any one action increase with the intensity of application of control.     

Defouling and cleaning using nanobubbles on stainless steel

The present work demonstrates that nanobubbles can be used as cleaning agents on stainless steel (SS) surfaces. Cleaning efficiency has been quantified. Using an Atomic Force Microscope (AFM), it was demonstrated that nanobubbles can be produced by electrochemical treatment on a SS surface either with or without adsorbed bovine serum albumin (BSA). After allowing adsorption on SS overnight, radio-labeled BSA was removed by electrochemically generated nanobubbles, and then the remaining BSA on the surface was quantified by radioactivity measurement. The results indicate that nanobubbles can remove >10% of the protein in each 3-min electrochemical treatment while in a control group, washing with water and electrolyte resulted in no more than 3% of the protein being removed each time. Cleaning of conducting surfaces by nanobubbles is promising in any system where fouling occurs in biomedia.     

Commensalism or mutualism: conditional outcomes in a branchiobdellid–crayfish symbiosis

A growing body of evidence suggests that the costs and benefits involved in cleaning interactions can vary over space and time depending on the environmental conditions. However, whether the same cleaners actually induce variable net outcomes in terms of host fitness remains unclear to date. Branchiobdellid annelids are generally regarded as commensals or rarely parasites of their freshwater crayfish hosts, but a recent study suggests that they may also function as cleaning organisms. Under natural conditions, crayfish can experience fouling of the exposed surfaces of their exoskeletons and their gills (e.g., epibiosis) by various epibionts and particles of organic debris, and branchiobdellids graze on these sources of fouling. Here, we examined the extent to which variation in fouling pressure in the environment alters the outcome of the interaction between branchiobdellids and their crayfish host Cambaroide similis. A series of manipulations were performed in artificial environments designed to simulate either high or low fouling pressure. We used crayfish growth rates and mortality as direct measurements of the net costs and benefits of cleaning. Branchiobdellids had no significant effect on crayfish growth or mortality when cultured under low fouling pressure. However, their presence had a significant positive impact on host growth rates when cultured under high fouling pressure. These results suggest that the relationship between crayfish and branchiobdellids can fluctuate between commensalism and mutualism depending mainly on the environmental fouling pressure. We hypothesize that the outcome of cleaning interactions may largely depend on the factors directly related to the need for cleaning, such as parasite loads or fouling pressure.