Functionality and composition of marine biofilms on antifouling coatings.

Marine biofilms are assemblages of microbial cells irreversibly attached to living or non-living surfaces, embedded in a self-produced matrix of hydrated extracellular polymeric substances (EPS). The phenomenon of biofouling occurs upon the adhesion and accumulation of biofilms, composing the primary colonizers that are capable of EPS production, followed by the sequential growth of secondary colonizers on submerged structures. Biofouling constitutes a significant issue in marine industries (e.g. maritime transportation) and problems related to biofilm fouling include an increase in drag force, modification of surface properties (e.g. metal corrosion) and production of chemical compounds with inhibition effects to other foulers. The use of powerful biocides exhibits a good performance against biofouling, however, often their efficacy is evident to a lesser degree against biofilms. These chemically active compounds have been found to have toxicity effects for marine life and there is a need to discover high-performance environmentally acceptable products.

The aim of the present study was to investigate the biofilm community composition and gene-expression on commercial antifouling (AF) coatings employing next-generation sequencing approaches. Natural mixed-species biofilms were examined after a four-month immersion of two commercial AF coatings, including a biocidal (BAF) and a fouling release (FR), and a control non-treated surface in Langstone Harbour UK. Replicated biofilm samples were used for nucleic acid extraction and sequenced targeting the 16S rRNA gene and metatranscriptome.

We uncovered distinct biofilm community profiles between the two coatings; the BAF samples were dominated by Bacillariophyceae (diatoms), contrary to the FR and control samples where Oscillatoriophycideae (phylum Cyanobacteria) were prevailing. Alphaproteobacteria and Gammaproteobacteria contributed to a high abundance in all samples. Biofilms on BAF samples exhibited a lower species diversity compared to the FR. Here, we introduce a set of functional genes present across all biofilm-associated communities and highlight the differing gene transcriptional profiles in biocidal treatments. The gene transcriptional analysis uncovered highly enriched genes coding for proteins involved in biofilm regulation and formation. We demonstrated that biocidal-associated biofilms harbor genes that regulate defense mechanisms. Overall, the findings highlight links between differentially expressed protein functions and effects of AF coating type during biofilm development. We anticipate these results to contribute towards further development of antibiofilm strategies and fill gaps related to marine biofilm functions.