Sea Technology

DEC 2018

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28 ST | December 2018 www.sea-technology.com additional pigments, which play other associated roles and are often specific to a particular type of algae. The collections of pigments in microalgal samples are regu- larly used in oceanography as broad fingerprints of the different algal groups in those samples, and we've ad- opted the same approach to characterize slime. Biofilm pigment analysis by high-performance liquid chromatog- raphy (HPLC) has revealed that in at least some experi- ments, several coatings are well-colonized by a particu- lar type of microalgae that is effectively absent from other coatings. Fluorescent Microscopy. Another property of microal- gal pigments is that they auto-fluoresce at different wave- lengths—they capture short wavelength light (ultraviolets and blues), absorb some of the energy, and then re-emit the light at longer wavelengths (oranges and reds). We can examine slime auto-fluorescence by epifluorescence microscopy and identify the diatoms (deep red) and cy- anobacteria (orange), confirming visually the output of pigment analysis by HPLC. Metagenomics. Metagenomics is another way to get a broad view of the total community in a fouling biofilm. We've been partnering with university microbiologists and bioinformaticians to look at how bacterial diversity and total fouling community diversity reflect the influ- ences of the underlying coating as well as biofilm ma- turity. AkzoNobel biology team researchers have extracted DNA from hundreds of slime samples, and each new result offers an exciting insight as to how communities form. Biomass. While community is important, we also want to be able to pair the type of biofilms with reli- able and objective measurements of quantity. To esti- mate total biomass, we've once again taken advantage of the fact that most ship slime contains photosynthetic, pigmented microalgae. In oceanography, the amount of chlorophyll in a body of water is a long-established proxy for how much photosynthetic microalgal biomass is floating in the sea. Chlorophyll absorbs red light and reflects green light, which is why it appears green, and it has similar characteristic absorption properties for other light wavelengths. If you can measure how much light is absorbed and reflected by photosynthetic biomass, you can approximate how much biomass there is. Multispec- tral biomass imaging, as this approach is called, is how the global marine microalgal conversion of sunshine to biomass is mapped from space by satellites. We've been developing similar methods to benchmark coating per- formance in lab assays, immersion trials and on ships, and we think not only about how much biomass is in slime but how it is distributed across the surface of a ship. Optical Coherence Tomography. How do biological properties pair up with physical properties, such as thick- ness, surface roughness, texture and viscoelasticity? As of a few years ago, it was a real challenge to measure the surfaces of biofilms—laser light reflected and scattered from the surface, indentation methods just deformed the surface, and microscopy could only image very small surface areas. But in the last few years, biofilm imaging has opened up with the adoption of a technology called optical co- herence tomography (OCT). OCT lets us image down through living biofilms over a surface area approximately the size of a penny. For the past three years, we've been using OCT imaging to get a closer look at the biofilms that grow on different coatings and developed methods to convert image data to biofilm topography, thickness, biovolume and surface roughness data. OCT imaging can also collect real-time video, and we're exploring how fouling biofilms on different coatings respond struc- turally to hydrodynamic shear. Looking Ahead One of our main objectives is to develop biological and physical predictors of biofilm drag, so as to incor- porate those metrics into coating development. Biofilms are natural superstructures and are not an easy challenge to address, which is why we are actively applying the investigative methods outlined here together with tech- niques from across the diverse field of biofilm science in our development of next-generation slime-free coating technologies. In parallel with biological method development, the hydrodynamics and marine biology research teams have been developing both in-house and collaborative approaches to measure the drag of slime on coatings. With flow cells and rotating disc systems, collaborative projects and in-house experiments, we are working to understand which methods are best suited to tie slime hydrodynamics and biophysical properties together. ST Jennifer Longyear is a research biologist in the fouling control team within AkzoNobel's Marine and Protective Coatings business. Longyear earned her undergraduate degree at Cornell University before moving to Canada to study for a master's degree in oceanography at Dalhousie University. She leads the Marine Biology Research Project and was instrumental in devel- oping a bioassay-based screening process to speed up fouling testing for AkzoNobel's Intersleek 1100SR project. Marie Dale is a research biologist in the fouling control team within Ak- zoNobel's Marine and Protective Coatings business. She earned her un- dergraduate degree at Plymouth University before joining AkzoNobel. Dale designs new methodology to assess, predict and quantify the fouling control performance of surfaces against biofouling alongside research into characterization of marine biofilms. OCT imaging reveals highly visible differences in slime topography for biofilms grown over 13 months on nine different coatings, including both biocidal and nonbiocidal coatings.

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