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Steelmaking slags are prospective base materials for seaweed beds, resulting from a continuous process of biofouling, starting from biofilm formation and leading to growing algae. While focusing on biofilm formation, we investigated specific features of steelmaking slags when utilized as a base for seaweed beds by comparing the bacterial communities in marine biofilms between steelmaking slags and artificially produced ones. Genomic DNA was extracted from the biofilms collected on days 3 and 7, and partial 16S rRNA libraries were generated and sequenced by second-generation next-generation sequencing. The read sequences were analyzed using QIIME 2™, then heatmaps and non-metric multidimensional scaling based on the Bray–Curtis dissimilarity index in the R program. Rhodobacteraceae and Flavobacteriaceae were the most dominant family members in all samples on both days 3 and 7. However, Mariprofundus, comprising iron-oxidative bacteria, was predominantly detected in the samples of steelmaking slags on day 7. This suggested that the growth of Mariprofundus was dependent on Fe(II) ion concentration and that steelmaking slags eluted Fe(II) ions more easily than artificial slags. In contrast, Sulfurovaceae, sulfur-oxidizing bacteria, were dominantly present in all samples on day 3, but decreased by day 7, regardless of the sulfur content. It was supposed that engine oil-derived sulfur compounds strongly influenced Sulfurovaceae growth, whereas slag-derived sulfur compounds did not. Heatmap analysis indicated that the submersion period significantly influenced the bacterial communities, regardless of the differences in the main slag content ratios. Summarizing these results, the elution characteristics of steelmaking slags have the potential to influence the formation of marine biofilms, and this formation is significantly influenced by environmental conditions. [ABSTRACT FROM AUTHOR]

The evaluation of biofilm formation is important, given the ubiquity and problematic nature of biofilms in industrial and medical settings, as well as in everyday life. Basically, biofilms are formed on substrates. Therefore, it is essential to consider the properties of the substrates during biofilm evaluation. The common dye staining method to evaluate biofilm formation requires a short evaluation time and enables the evaluation of a large area of the sample. Furthermore, it can be easily determined visually, and quantitative evaluation is possible by quantifying color adsorption. Meanwhile, the dye staining method has the problem of adsorption even on substrate surfaces where no biofilm has formed. Therefore, in this study, we focused on Ag+ reduction reaction to devise a novel biofilm evaluation method. Ag+ is highly reductive and selectively reacts with organic substances, such as saccharides, aldehydes, and proteins contained in biofilms, depositing as metallic Ag. First, to simply evaluate biofilm formation, we used a glass substrate as a smooth, transparent, and versatile oxide material. We observed that the amount of Ag deposited on the substrate was increased proportionally to the amount of biofilm formed under light irradiation. Upon comparing the Ag deposition behavior and adsorption behavior of crystal violet, we discovered that for short immersion times in AgNO3 solution, Ag deposition was insufficient to evaluate the amount of biofilm formation. This result suggests that the Ag reduction reaction is more insensitive than the crystal violet adsorption behavior. The results of the Ag deposition reaction for 24 h showed a similar trend to the crystal violet dye adsorption behavior. However, quantitative biofilm evaluation using the proposed method was difficult because of the Ag+ exchange with the alkali metal ions contained in the glass substrate. We addressed this issue by using the basic solution obtained by adding an ammonia solution to aqueous AgNO3. This can cause Ag+ to selectively react with the biofilm, thus enabling a more accurate quantitative evaluation. The optimum was determined at a ratio of distilled water to aqueous ammonia solution of 97:3 by weight. This biofilm was also evaluated for materials other than ceramics (glass substrate): organic material (polyethylene) and metal material (pure iron). In the case of polyethylene, a suitable response and evaluation of biofilm formation was successfully achieved using this method. Meanwhile, in the case of pure iron, a significantly large lumpy deposit of Ag was observed. The likely reason is that Ag precipitation occurred along with the elution of iron ions because of the difference in ionization tendency. It could be concluded that the detection of biofilm formation using this method was effective to evaluate biofilm formation on materials, in which the reduction reaction of [Ag(NH3)2]+ does not occur. Thus, a simple and relatively quantitative evaluation of biofilms formed on substrates is possible using this method. [ABSTRACT FROM AUTHOR]

Biofilms are the result of bacterial activity. When the number of bacteria (attached to materials' surfaces) reaches a certain threshold value, then the bacteria simultaneously excrete organic polymers (EPS: extracellular polymeric substances). These sticky polymers encase and protect the bacteria. They are called biofilms and contain about 80% water. Other components of biofilm include polymeric carbon compounds such as polysaccharides and bacteria. It is well-known that biofilms cause various medical and hygiene problems. Therefore, it is important to have a sensor that can detect biofilms to solve such problems. Graphene is a single-atom-thick sheet in which carbon atoms are connected in a hexagonal shape like a honeycomb. Carbon compounds generally bond easily to graphene. Therefore, it is highly possible that graphene could serve as a sensor to monitor biofilm formation and growth. In our previous study, monolayer graphene was prepared on a glass substrate by the chemical vapor deposition (CVD) method. Its biofilm forming ability was compared with that of graphite. As a result, the CVD graphene film had the higher sensitivity for biofilm formation. However, the monolayer graphene has a mechanical disadvantage when used as a biofilm sensor. Therefore, for this new research project, we prepared bilayer graphene with high mechanical strength by using the CVD process on copper substrates. For these specimens, we measured the capacitance component of the specimens' impedance. In addition, we have included a discussion about the possibility of applying them as future sensors for monitoring biofilm formation and growth. [ABSTRACT FROM AUTHOR]

Steelmaking slags are a promising resource as artificial seaweed beds for the reconstitution of marine environments. To grow seaweed well, the formation of biofilms is an essential process in biofouling. This study focused on the formation of initial biofilms on steelmaking slag samples and analyzed the resulting bacterial communities using the next-generation sequencing technique. Three types of steelmaking slag were submerged in an area of Ise Bay in Mie Prefecture, Japan, for 3 and 7 days in the summer and winter seasons to allow the formation of biofilms. The bacterial communities of these biofilms were richer in sulfur-oxidizing bacteria compared to the biofilms formed on polyurethane sponges. It was found that Helicobacteraceae dominantly grew on the biofilms formed on the slag samples. This shows that steelmaking slags have potential to be used as artificial seaweed beds and marine water purifiers. [ABSTRACT FROM AUTHOR]

Thus far, biofouling on material surfaces has been investigated from various viewpoints, and concrete methods for its evaluation have been proposed. Biofilms, which are formed by bacterial activities, are essential components of biofouling. They play an important role in the occurrence of biofouling on the materials of structures, which leads to serious economic loss. Therefore, the establishment of countermeasures for biofilm formation and its control are needed urgently. In addition, appropriate evaluation techniques to measure biofilm formation are required. Thus far, we have used scientific evaluation devices and techniques such as an optical microscope and Raman spectroscopy to evaluate biofouling/biofilms. In this study, we used the silane coating of dispersed silver and copper nanopowder rather than that of dispersed organometals. Specimens were immersed into a laboratory biofilm reactor. Then, the biofouling behavior on the sheets was investigated using an optical microscope, Raman spectroscopy, a focused ion beam system (FIB), and scanning electron microscopy (SEM). The optical-microscope observations showed many deposits on the specimens without any metallic dispersions. Although the amount of deposits on the specimens decreased with copper dispersions, many deposits were still observed on them with silver dispersion. These deposits were not confirmed by Raman spectroscopy because of the surface plasmon resonance of silver. Next, we observed and analyzed the specimens using the FIB system (combination of FIB–SEM and EDX) instead of Raman spectroscopy. The SEM image showed that the deposition had formed pores and irregularities on the specimens. FIB–SEM confirmed the existence of deposition on coating layers and revealed that it originated from biooraganisms. Based on these experiments, we could conclude that the structure of antifouling coating could be observed and analyzed using a combination of FIB–SEM and EDX even when other analysis methods are not useful because of various reasons. [ABSTRACT FROM AUTHOR]