The effect of a biofilm-forming bacterium Tenacibaculum mesophilum D-6 on the passive film of stainless steel in the marine environment.

The microbiologically influenced corrosion of 304 stainless steel in the presence of a marine biofilm-forming bacterium Tenacibaculum mesophilum D-6 was systematically investigated by means of electrochemical techniques and surface analyses to reveal the effect of the selective attachment and adsorption of the biofilms on the passivity breakdown of the stainless steel. It was found that the T. mesophilum D-6 was electroactive and could oxidize low valent cations and metal, facilitating the local dissolution of the passive film and the substrate in the film defects, nearly doubling the surface roughness. The biofilms of T. mesophilum D-6 with mucopolysaccharide secreta and chloride ions tended to preferentially adsorb at the defects of the passive film on the steel, yielding non-homogeneous microbial aggregates and local Cl- enrichment there. The adsorption of the bacteria and chloride ions reduced the thickness of passive film by 23.9%, and generate more active sites for pitting corrosion on the passive film and more semiconducting carrier acceptors in the film. The maximum current density of the 304 SS in the presence of T. mesophilum D-6 was over one order of magnitude higher than that in the sterile medium, and the largest pit was deepened 3 times.

Marine Biofilms with Significant Corrosion Inhibition Performance by Secreting Extracellular Polymeric Substances.

The development of environmentally friendly and sustainable corrosion protection technologies is a longstanding yet difficult problem, especially for the marine environment. The utilization of living biofilms isolated from local environments is an effective strategy for infrastructure protection. In this study, three aerobic marine bacteria, Tenacibaculum mesophilum D-6, Tenacibaculum litoreum W-4, and Bacillus sp. Y-6, with strong biofilm-forming abilities were isolated and evaluated for the corrosion protection of X80 carbon steel. The corrosion inhibitory effect of the bacteria was found to be closely related to their biofilm-forming abilities. This conclusion was corroborated by biofilm characterization, electrochemical tests, weight loss analysis, and corrosion product analysis. Moreover, secreted extracellular polymeric substances were identified to play significant roles in corrosion inhibition. Herein, we proposed a novel, eco-friendly, and cost-effective method for corrosion protection of carbon steels in the marine environment, providing guiding principles for identifying corrosion inhibitory bacteria from the local marine environment.

Combat biofouling with microscopic ridge-like surface morphology: a bioinspired study.

Biofouling refers to the unfavourable attachment and accumulation of marine sessile organisms (e.g. barnacles, mussels and tubeworms) on the solid surfaces immerged in ocean. The enormous economic loss caused by biofouling in combination with the severe environmental impacts induced by the current antifouling approaches entails the development of novel antifouling strategies with least environmental impact. Inspired by the superior antifouling performance of the leaves of mangrove tree Sonneratia apetala, here we propose to combat biofouling by using a surface with microscopic ridge-like morphology. Settlement tests with tubeworm larvae on polymeric replicas of S. apetala leaves confirm that the microscopic ridge-like surface morphology can effectively prevent biofouling. A contact mechanics-based model is then established to quantify the dependence of tubeworm settlement on the structural features of the microscopic ridge-like morphology, giving rise to theoretical guidelines to optimize the morphology for better antifouling performance. Under the direction of the obtained guidelines, a synthetic surface with microscopic ridge-like morphology is developed, exhibiting antifouling performance comparable to that of the S. apetala replica. Our results not only reveal the underlying mechanism accounting for the superior antifouling property of the S. apetala leaves, but also provide applicable guidance for the development of synthetic antifouling surfaces.

The effects of model polysiloxane and fouling-release coatings on embryonic development of a sea urchin (Arbacia punctulata) and a fish (Oryzias latipes).

In recent decades attention has focused on the development of non-toxic fouling-release coatings based on silicone polymers as an alternative to toxic antifouling coatings. As fouling-release coatings gain market share, they will contribute to environmental contamination by silicones. We report effects of eight model polysiloxane and three commercial foul-release coatings on embryonic development of sea urchins and fish, Japanese medaka. We used model coatings because they have known composition and commercially available components and molecules leaching from these coatings have been partially characterized. The commercial fouling-release coatings are purported to be non-toxic and components are proprietary. Our goal was to expose embryos of well studied model animals to the coatings to determine if the complex mixtures leaching from the coatings impact development. Urchins were chosen because development is rapid and embryos can enter the non-slip layer over surfaces. Medaka was chosen because the female deposits the sticky eggs onto the anal fin and then scrapes them off onto surfaces. Embryos were confined in water over coatings in 24 well plates. Fresh model coatings had no effect on urchin development while commercial fouling-release coatings inhibited development. Fish embryos had delayed hatching, increased mortality of hatchlings and dramatically decreased ability of hatchlings to inflate the swim bladder and reduced hatching success on all coatings. After one-month immersion of coatings in running seawater to simulate initial application in the marine environment, sea urchin embryos died when placed over model silicones. Effects of the commercial coatings were reduced but included retarded development. Effects on fish embryos over leached coating were reduced compared to those of fresh coating and included decreased hatching success, decreased hatchling survival and inability to inflate the swim bladder for commercial coatings. These findings suggest, similar to medical conclusions, compounds leaching from silicone coatings can impact development and the topic deserves study.