The current study investigated the microbial community composition of the biofilms that developed on 11 commercial biocidal coatings, including examples of the three main historic types, namely self-polishing copolymer (SPC), self-polishing hybrid (SPH) and controlled depletion polymer (CDP), after immersion in the sea for one year. The total wet weight of the biofilm and the total bacterial density were significantly influenced by all coatings. Pyrosequencing of 16S rRNA genes revealed distinct bacterial community structures on the different types of coatings. Flavobacteria accounted for the dissimilarity between communities developed on the control and SPC (16%) and the control and SPH coatings (17%), while Alphaproteobacteria contributed to 14% of the dissimilarity between the control and CDP coatings. The lowest number of operational taxonomic units was found on Intersmooth 100, while the lowest biomass and density of bacteria was detected on other SPC coatings. The experiments demonstrated that the nature and quantity of biofilm present differed from coating to coating with clear differences between copper-free and copper-based biocidal coatings.

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Abstract:The common practice of counting bacteria using epifluorescence microscopy involves selecting 5-30 random fields of view on a glass slide to calculate the arithmetic mean which is then used to estimate the total bacterial abundance. However, not much is known about the accuracy of the arithmetic mean when it is calculated by selecting random fields of view and its effect on the overall abundance. The aim of this study is to evaluate the accuracy and reliability of the arithmetic mean by estimating total bacterial abundance and to calculate its variance using a bootstrapping technique. Three fixed suspensions obtained from a three-week-old marine biofilm were stained and dispersed on glass slides. Bacterial cells were counted from a total of 13,924 fields of view on each slide. Total bacterial count data obtained were used for calculating the arithmetic mean and associated variance and bias for sample field sizes of 5, 10, 15, 20, 25, 30, 35 and 40. The study revealed a non-uniform distribution of bacterial cells on the glass slide. A minimum of 20 random fields of view or a minimum of 350 bacterial cells need to be counted to obtain a reliable value of the arithmetic mean to estimate the total bacterial abundance for a marine biofilm sample dispersed on a glass slide.

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.

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