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Recently, studies have begun to identify oil-degrading bacteria and host-taxon specific bacterial assemblages associated with the coral holobiont, including deep-sea cold-water corals, which are thought to provide metabolic functions and additional carbon sources to their coral hosts. Here, we describe the identification of Marinobacter on the soft tissue of Lophelia pertusa coral polyps by Catalyzed Reporter Deposition Fluorescence in situ Hybridization (CARD-FISH). L. pertusa samples from three reef sites in the northeast Atlantic (Logachev, Mingulay and Pisces) were collected at depth by vacuum seal to eliminate contamination issues. After decalcification, histological processing and sagittal sectioning of the soft coral polyp tissues, the 16S rRNA-targeted oligonucleotide HRP-labelled probe Mrb-0625-a, and Cyanine 3 (Cy3)-labelled tyramides, were used to identify members of the hydrocarbon-degrading genus Marinobacter. Mrb-0625-a-hybridized bacterial cell signals were detected in different anatomical sites of all polyps collected from each of the three reef sites, suggesting a close, possibly intimate, association between them, but the purpose of which remains unknown. We posit that Marinobacter, and possibly other hydrocarbon-degrading bacteria associated with Lophelia, may confer the coral with the ability to cope with toxic levels of hydrocarbons in regions of natural oil seepage and where there is an active oil and gas industry presence., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Some studies have described the isolation and 16S rRNA gene sequence-based identification of hydrocarbon-degrading bacteria living associated with marine eukaryotic phytoplankton, and thus far the direct visual observation of these bacteria on micro-algal cell surfaces ('phycosphere') has not yet been reported. Here, we developed two new 16S rRNA-targeted oligonucleotide probes, PCY223 and ALGAR209, to respectively detect and enumerate the obligate hydrocarbonoclastic bacteria Polycyclovorans algicola and Algiphilus aromaticivorans by Catalyzed Reporter Deposition Fluorescence in situ Hybridization (CARD-FISH). To enhance the hybridization specificity with the ALGAR209 probe, a competitor probe was developed. These probes were tested and optimized using pure cultures, and then used in enrichment experiments with laboratory cultures of micro-algae exposed to phenanthrene, and with coastal water enriched with crude oil. Microscopic analysis revealed these bacteria are found in culture with the micro-algal cells, some of which were found attached to algal cells, and whose abundance increased after phenanthrene or crude oil enrichment. These new probes are a valuable tool for identifying and studying the ecology of P. algicola and A. aromaticivorans in laboratory and field samples of micro-algae, as well as opening new fields of research that could harness their ability to enhance the bioremediation of contaminated sites., (Copyright © 2018 Elsevier B.V. All rights reserved.)