Screening of Surface-associated Bacteria from the Mexican Red Alga Halymenia floresii for Quorum Sensing Activity

Abstract

Macroalgae host a dense bacterial epibiome forming surface biofilms, which act as a biological defense by protecting the surface from macrofoulers. During experimental cultivation of Halymenia floresii (Rhodophyta, Halymeniales) under Integrated MultiTrophic Aquaculture (IMTA), the culture tanks remained clean of any exogenous algal colonization, and the surface of the H. floresii thalli was remarkably free from any fouling organisms. The presence of Halymenia also appeared to restrict the establishment of opportunist green algae and the colonization of barnacles usually impairing the cultures. To date, nothing is known about the diversity and biological potential of H. floresii epibionts. Hence, to better understand their epiphytic bacterial community, surface-associated bacteria from distinct H. floresii samples, beach-cast, integrated multi trophic aquaculture cultivar, and cultivar cylinders, were isolated. Thirty-one axenic bacterial strains belonging to 3 phyla, 20 genera, and 25 species were identified by 16S rRNA gene sequencing. Following isolation, they were screened for the production of quorum sensing (QS) signals, since these communication signals play a vital role in biofilm formation. All, except one, isolates were identified as gram-negative; hence, acylated homoserine lactones (AHLs) were focused upon. Using the reporter strain Escherichia coli pSB406, the isolates were screened for their ability to induce luminescence. Of 31 isolates screened, 17 strains, including Pseudoalteromonas arabiensis, Pseudoalteromonas sp. (B5BC and B6.1BC), Pseudoalteromonas mariniglutinosa, Vibrio owensii, Tenacibaculum sp., Maribacter sp., Spongiimicrobium salis, Aquimarina sp., Kordiimonas sp., Alteromonas sp. (B12CC and B16CC), Roseobacter sp., Erythrobacter sp., Ruegeria lacuscaerulensis, and Epibacterium sp., exhibited the presence of extracellular QS signals. Thus, the presence of QS bacteria on the surface of H. floresii was demonstrated for the first time. Our results may open a new direction to investigate the host—QS bacteria interactions.