Impacts of UV-C irradiation on marine biofilm community succession

Marine biofilms are diverse microbial communities and important ecological habitats forming on surfaces submerged in the ocean. Biofilm communities resist environmental disturbance, making them a nuisance to some human activities (‘biofouling’). Anti-fouling solutions rarely address the underlying stability or compositional responses of these biofilms. Using bulk measurements and molecular analyses, we examined temporal and UV-C antifouling-based shifts in marine biofilms in the coastal Western North Atlantic Ocean during early fall. Over a 24-d period, bacterial communities shifted from early dominance of Gammaproteobacteria to increased proportions of Alphaproteobacteria, Bacteroidia and Acidimicrobiia. In a network analysis based on temporal covariance, Rhodobacteraceae (Alphaproteobacteria) nodes were abundant and densely connected with generally positive correlations. In the eukaryotic community, persistent algal, protistan, and invertebrate groups were observed, although consistent temporal succession was not detected. Biofilm UV-C treatment at 13 and 20 days resulted in losses of chlorophyll a and transparent exopolymer particles, indicating biomass disruption. Bacterial community shifts suggested that UV-C treatment decreased biofilm maturation rate and was associated with proportional shifts among diverse bacterial taxa. UV-C treatment was also associated with increased proportions of protists potentially involved in detritivory and parasitism. Older biofilm communities had increased resistance to UV-C, suggesting that early biofilms are more susceptible to UV-C based antifouling. The results suggest that UV-C irradiation is potentially an effective antifouling method in marine environments in terms of biomass removal and in slowing maturation. However, as they mature, biofilm communities may accumulate microbial members that are tolerant or resilient under UV-treatment. Importance Marine biofilms regulate processes from organic matter and pollutant turnover to eukaryotic settlement and growth. Biofilm growth and eukaryotic settlement interfering with human activities via growth on ship hulls, aquaculture operations, or other marine infrastructure are called ‘biofouling’. There is a need to develop sustainable anti-fouling techniques by minimizing impacts to surrounding biota. We use the biofouling-antifouling framework to test hypotheses about marine biofilm succession and stability in response to disturbance, using a novel UV-C LED device. We demonstrate strong bacterial biofilm successional patterns and detect taxa potentially contributing to stability under UV-C stress. Despite UV-C-associated biomass losses and varying UV susceptibility of microbial taxa, we detected high compositional resistance among biofilm bacterial communities, suggesting decoupling of disruption in biomass and community composition following UV-C irradiation. We also report microbial covariance patterns over 24 days of biofilm growth, pointing to areas for study of microbial interactions and targeted antifouling.

Draft Genome Sequencing of Pseudoalteromonas tetraodonis Strain kknpp56, a Potent Biofilm-Forming Bacterium Isolated from Early-Stage Marine Biofilm

Pseudoalteromonas tetraodonis strain kknpp56 is an exopolysaccharide (EPS)-producing marine bacterium that forms potent biofilm. To determine the biosynthesis pathways involved in the EPS production of this bacterium, whole-genome sequencing was performed. The complete genome comes from one chromosome containing 3.72 Mbp of DNA with a G+C content of 41%.

Comparison of techniques for counting prokaryotes in marine planktonic and biofilm samples

Though a large number of techniques are available for the study of aquatic bacteria, the aim of this study was to establish a technique for analysing free-living and biofilm prokaryotic cells through laboratory assays. In particular, we wished to analyse the efficiency of ultrasound to detach and disrupt biofilm, to obtain an efficient stain treatment for quantifying free-living and biofilm prokaryotes in flow cytometry (FC), and to compare epifluorescence microscopy (EFM), scanning electron microscopy (SEM) and FC for quantifying free-living and biofilm prokaryotes#. Marine-grade plywood substrates were immersed in natural marine water that was conditioned for 12 days. At 6 and 12 days, water aliquots and substrates were removed to estimate free-living and biofilm prokaryote density. Ultrasound efficiently removed marine biofilm from substrates (up to 94%) without cell damage. FC analysis (unstained) reliably quantified marine plankton and young or mature biofilm prokaryotes compared with other staining (acridine orange, 4′,6-diamidino-2-phenylindole, propidium iodide and green fluorescent nucleic acid), EFM or SEM techniques. FC and SEM achieved similar results, while a high variability was observed in the EFM technique. FC was faster and more precise than SEM because the count is not dependent on the observer.

Using metabarcoding and « Diat.Barcode » database to perfom molecular identification on marine biofilms

Marine benthic diatoms highly contribute to biofilms formation, playing a crucial role on both living and artificial surfaces ‘colonization (Briand 2017, Salta 2013). However, their microscopic morphological identification is time consuming and requires a high expertise in taxonomy. We therefore decided to look toward molecular analyses and especially metabarcoding. In this study, we determine : (i) if the use of the “Diat.barcode” database, mostly developed for freshwater diatoms (Rimet 2019), is relevant to characterize marine biofilm communities, (ii) if the amplification of degenerated primers targeting the rbcL gene (Vasselon et al. 2017) could improve the diversity of marine diatom biofilms, and (iii) if molecular and morphological analyses could be correlated.A large majority of OTUs (>95%) was affiliated using the “Diat.barcode” database and the pipeline FROGS, with coverage and affinity values above 80%. OTUs tables contained 75% of diatom species already reported from marine environment, with 82% belonging to the pennates group. The use of degenerated primers significantly improved richness and diversity. Moreover, it allowed us to identify taxa that were not present before, as Iconella, Sellaphora and Coronia. Finally, we showed higher richness and diversity, but also a higher repeatability (replicates closeness) leading to a better clustering with metabarcoding. We found differences in terms of biomarkers, but more broadly, we were able to correlate significantly (r = 0,404; p<0.0001) diatom assemblages.While the latest version of “Diat.barcode” database contains only 12.4% species referenced as marine, it appears to be a powerful tool, even on biofilm samples from the Mediterranean, Baltic seas and Indian Ocean. Furthermore, we confirmed the relevance of degenerated primers to amplify a higher diversity of diatoms. Finally, beta-diversity similarity using molecular and microscopic analysis appeared positive, leading to the conclusion that the two methods should be used in a complementary way.