Diversity Of Bacterial Community On The Surface Of Steel And Marine Paint In Temperate Coastal Marine Waters

Marine biofouling has been given increasingly attention for its important impacton marine corrosion to steel structure constructions in the sea, such as Ocean-goingvessels and platform for petroleum, etc. The first step of marine biofouling isattachment of bacteria to the submerged surfaces in the seawater, while it plays a keyrole in the macrofouling and microbiologically influenced corrosion (MIC). In thepaper, the predominant bacteria of the rust layer on Q235steel immersed in seawaterfor one year and their diversity are analyzed by PCR-Restriction Fragment LengthPolymorphism (RFLP).The same research has been made on the marine paint MEPand IP, as well as the316L stainless steel.The microorganisms on the surface of substrate in different stages are observedby scanning electron microscopy (SEM) and Fluorescence microscopy. The resultsshow that the number of microorganisms attaching on the surface of316L stainlesssteel increases significantly through time in the first15days. Both the MEP and IPmarine paints have positive bactericidal effect, while the traditional marine paint IPperformances better.To study the bacterial diversity of the rust layer on Q235steel immersed inseawater, the bacterial community structures are investigated through16S rDNAanalysis, which results in192clones’ randomly selecting and sequencing. After thesequences are checked,64OTUs are obtained in all, so it indicates that the rust layercontained high bacterial diversity. These64clones could be divided into11phylotypes: Proteobacteria, Bacteroidetes, Acidobacteria, Planctomycetes, Nitrospirae,Firmicutes, Chloroflexi, Verrucomicrobia, Chlorobi, Actinobacteria and Spirochaetes,but most of these sequences belong to uncultivated bacteria．Proteobacteria, especiallyAlphaproteobacteria, whose percentage is46％and53％respectively in the outer and inner rust layers, is the dominant components. Bacteroides is also one of thedominant components and takes up16%and21.1%respectively. However, there is aspecial phylum, which is Firmicutes, occupying16%in the inner rust layer. Otherspecial phylums also exist in the outer and inner rust layers, but all of them of smallnumbers. The bacterial communities in the outer and inner rust layers also have differfrom each other in phylogenetical divergence.The bacterial community structures on the surface of these two kinds of marinepaint, IP and MEP, as well as316L stainless steel immersed in seawater areinvestigated through16S rDNA analysis, too. Phylogenetic analysis of26OTUsshows that the bacterial phylotypes of sample IP are made up by two phylums ofbacteria, Bacteroides and Proteobacteria. γ-Proteobacteria takes up65.1%of theclone number, but α-Proteobacteria has11OTUs and is more than γ-Proteobacteria.The bacterial phylotypes of sample MEP is made up by three phylums bacteria,Bacteroides, Planctomycetes and Proteobacteria. γ-Proteobacteria andα-Proteobacteria are the dominant components and their percentage are38.7％and39.8％respectively, but the number of α-Proteobacteria’s OTUs is14, which ismore than half of all. The result of316L stainless steel is similar to sample IP, but α-Proteobacteria takes up72.3%of the clone number.MEP is a tin free self-smoothening and self-polishing antifouling paint, whichdoes not contain any harmful active agents to environment, nevertheless, itsbactericidal efficiency is lower than traditional marine paint adding cuprous oxide andfungicides. In addition, Cycloclasticus, a marine polycyclic aromatic hydrocarbons(PAHs) decomposing bacteria, is found on both marine paints’ surfaces. It canbiodegrade dibenzofurans, naphthalene and phenanthrene and cause damage to thecoating.