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Marine biofouling is a worldwide problem affecting maritime industries. Global concerns about the high toxicity of antifouling paints have highlighted the need to develop less toxic antifouling coatings. Chitosan is a natural polymer with antimicrobial, antifungal and antialgal properties that is obtained from partial deacetylation of crustacean waste. In the present study, nanocomposite chitosan-zinc oxide (chitosan-ZnO) nanoparticle hybrid coatings were developed and their antifouling activity was tested. Chitosan-ZnO nanoparticle coatings showed anti-diatom activity against Navicula sp. and antibacterial activity against the marine bacterium Pseudoalteromonas nigrifaciens. Additional antifouling properties of the coatings were investigated in a mesocosm study using tanks containing natural sea water under controlled laboratory conditions. Each week for four weeks, biofilm was removed and analysed by flow cytometry to estimate total bacterial densities on the coated substrates. Chitosan-ZnO hybrid coatings led to better inhibition of bacterial growth in comparison to chitosan coatings alone, as determined by flow cytometry. This study demonstrates the antifouling potential of chitosan-ZnO nanocomposite hybrid coatings, which can be used for the prevention of biofouling.

Polyacrylonitrile and its TiO 2 composites were electrospun into nanofibers in N, N'-dimethylformamide for photocatalysis and antifouling experiments. The resultants nanofibers were characterized using field emission scanning microscope, Fourier transform infrared spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy and contact angle analyses. Fourier transform infrared spectroscopy confirmed the formation of polyacrylonitrile-TiO 2 composite nanofibers with their diameter ranging from 10 to 340 nm. The x-ray photoelectron spectroscopy results indicate the formation of O-Ti-C bonds on polyacrylonitrile-TiO 2 matrix. polyacrylonitrile-TiO 2 and polyacrylonitrile nanofiber surfaces showed superhydrophobicity with water contact angle of 155 ± 1 and 154 ± 1, respectively at 120 s. The photocatalytic properties of polyacrylonitrile nanofibers and polyacrylonitrile-TiO 2 nanofibers were investigated under a simulated visible light source of 1000 W/m 2 using methylene blue. About 90% of methylene blue was degraded within 3 h of exposure using polyacrylonitrile-TiO 2 nanofibers while 55% methylene blue degradation was achieved for polyacrylonitrile nanofibers. Photoluminescence experiment conducted on both materials showed that polyacrylonitrile-TiO 2 could produce OH radicals 10-fold compared to polyacrylonitrile nanofibers. Antimicrobial tests were conducted using E. coli and Bacillus sp. The results showed that only polyacrylonitrile-TiO 2 under visible light hindered the growth of these bacteria with a greater effect on the Gram-positive bacterium, Bacillus sp. The photo-degradation and microbial growth inhibition properties of polyacrylonitrile-TiO 2 showed that the material could be used as an antifouling material under visible light.

Efficiency of nanocomposite zinc oxide-chitosan antimicrobial polyethylene packaging films for the preservation of quality of vegetables was studied using okra Abelmoschus esculentus. Low density polyethylene films (LDPE) coated with chitosan-ZnO nanocomposites were used for packaging of okra samples stored at room temperature (25 °C). Compared to the control sample (no coating), the total bacterial concentrations in the case of chitosan and nanocomposite coatings were reduced by 53% and 63%, respectively. The nanocomposite coating showed a 2-fold reduction in total fungal concentrations in comparison to the chitosan treated samples. Results demonstrate the effectiveness of the nanocomposite coatings for the reduction of fungal and bacterial growth in the okra samples after 12 storage days. The nanocomposite coatings did not affect the quality attributes of the okra, such as pH, total soluble solids, moisture content, and weight loss. This work demonstrates that the chitosan-ZnO nanocomposite coatings not only maintains the quality of the packed okra but also retards microbial and fungal growth. Thus, chitosan-ZnO nanocomposite coating can be used as a potential coating material for active food packaging applications.

For the first time, densities and diversity of microorganisms developed on the ocean glider were investigated using flow cytometry and Illumina MiSeq sequencing of 16S and 18S rRNA genes. Ocean gliders are autonomous buoyancy-driven underwater vehicles, equipped wi th sensors continuously recording physical, chemical, and biological parameters. Biofilms on the glider were exposed to periodical oscillations of salinity, oxygen, temperature, pressure, depth and light, due to periodic ascending and descending of the vehicle. Among the unpainted surfaces, the highest microbial abundance was observed on the bottom of the glider's body, while the lowest density was recorded on the glider's nose. Antifouling pai nts had the lowest densities of microorganisms. Multidimentional analysis showed that microbial communities formed on unpainted parts of the glider shared some similarity wi th non-toxic paint but they were significantly different from ones on toxic antifouling paint and seawater.

Marine sources have been known to yield novel compounds with a wide range of bioactivity with various commercial applications. In this study, the abilities of bacteria isolated from eight marine organisms to produce α-amylase were examined. All eight organisms were found to harbor amylase producing bacteria. Two bacterial species isolated from the green alga Ulva rigida and the sponge Mycale sp. were further identified and their α-amylases were purified and characterized. The bacterial species isolated from U. rigida and Mycale sp. were identified by DNA sequencing as Cellulosimicrobium sp. and Demequina sp., respectively. Cellulosimicrobium sp. obtained maximum cell growth and amylase production at 29.C and in the presence of lactose as a carbon source. Optimal cell growth and amylase production by Demequina sp. was observed at 35.C. While lactose enhanced cell growth of Demequina sp., maximum amylase production was found when fructose and glycerol were the available sources of carbon. Both strains grew better in the presence of tryptone, whilst peptone stimulated amylase production. Maximal cell growth and amylase production by both of the strains was found at a medium salinity of 3% NaCl.

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In the current study, chitosan coatings were fabricated on plastic substrata and investigated for their antifouling activities. Scanning Electron Microscopy (SEM) and water contact angle measurement (WCA) of the fabricated chitosan films showed smooth and hydrophilic surface with WCA below 60°. Chitosan coating on plastic substrate showed 88% reduction in settlement of bryozoan Bugula neritina larvae compare to the control after 3 hours incubation in dark conditions with no larval mortality during the experiment. The antimicrobial activity of chitosan was evaluated by coating of plastic panels with the prepared chitosan solution and immersing the coated samples in seawater with controlled environmental conditions. Biofilms scraped from immersed chitosan coated panels showed no bacteria after 1 week immersion. After the second week of immersion, less than 1500 bacteria/mm2 was observed on the chitosan-coated panels compared to more than 105 bacteria/mm2 on uncoated ones. Thus, this study prove the efficiency of chitosan coatings against micro- and macro-fouling.