Low Densities of Epiphytic Bacteria from the Marine Alga Ulva australis Inhibit Settlement of Fouling Organisms

Abstract

Bacteria that produce inhibitory compounds on the surface of marine algae are thought to contribute to the defense of the host plant against colonization of fouling organisms. However, the number of bacterial cells necessary to defend against fouling on the plant surface is not known. Pseudoalteromonas tunicata and Phaeobacter sp. strain 2.10 (formerly Roseobacter gallaeciensis) are marine bacteria often found in association with the alga Ulva australis and produce a range of extracellular inhibitory compounds against common fouling organisms. P. tunicata and Phaeobacter sp. strain 2.10 biofilms with cell densities ranging from 10 2 to 10 8 cells cm ؊2 were established on polystyrene petri dishes. Attachment and settlement assays were performed with marine fungi (uncharacterized isolates from U. australis), marine bacteria (Pseudoalteromonas gracilis, Alteromonas sp., and Cellulophaga fucicola), invertebrate larvae (Bugula neritina), and algal spores (Polysiphonia sp.) and gametes (U. australis). Remarkably low cell densities (10 2 to 10 3 cells cm ؊2 ) of P. tunicata were effective in preventing settlement of algal spores and marine fungi in petri dishes. P. tunicata also prevented settlement of invertebrate larvae at densities of 10 4 to 10 5 cells cm ؊2 . Similarly, low cell densities (10 3 to 10 4 cells cm ؊2 ) of Phaeobacter sp. strain 2.10 had antilarval and antibacterial activity. Previously, it has been shown that abundance of P. tunicata on marine eukaryotic hosts is low (<1 ؋ 10 3 cells cm ؊2 ) (T. L. Skovhus et al., Appl. Environ. Microbiol. 70:2373-2382, 2004). Despite such low numbers of P. tunicata on U. australis in situ, our data suggest that P. tunicata and Phaeobacter sp. strain 2.10 are present in sufficient quantities on the plant to inhibit fouling organisms. This strongly supports the hypothesis that P. tunicata and Phaeobacter sp. strain 2.10 can play a role in defense against fouling on U. australis at cell densities that commonly occur in situ.

Mini-review: Inhibition of biofouling by marine microorganisms

“…For instance, Pseudoalteromonas tunicata and Phaeobacter sp. strain 2.10 (formerly Roseobacter gallaeciensis) isolated from the alga U. australis inhibited larval settlement of the bryozoan Bugula neritina at densities of 10 3 to 10 5 cells cm À2 , which are similar to the densities of these bacteria under natural conditions (Rao et al 2007). Multispecies biofilms with similar composition to those from the alga Fucus vesiculosus inhibited the settlement of cyprid larvae of the barnacle Amphibalanus improvisus (Nasrolahi et al 2012).…”

“…Bacteria associated with the green alga Ulva lactuca have been shown to have antibacterial and antialgal activity (Table 4; Rao et al 2007;Kumar et al 2011). Eighty percent of epibiotic isolates from U. lactuca inhibited growth of the diatom Cylindrotheca fusiformis .…”

Phaeobacter gallaeciensis genomes from globally opposite locations reveal high similarity of adaptation to surface life

“…Despite this genomic evidence for a surfaceattached lifestyle (Supplementary Material S13), colonization of P. gallaeciensis has only been investigated for one natural surface type, the green alga U. lactuca (Rao et al, 2007). Therefore, green fluorescent protein (GFP)-labeled cells of P. gallaeciensis DSM 17395 were added to a variety of micro-and macroalgae, crustacean tissue and driftwood.…”

“…Because of the competitive success of Phaeobacter spp. against fish and mollusc pathogens, ongoing research focuses on these organisms as probiotic agents in aquaculture (Rao et al, 2007;Porsby et al, 2008;Prado et al, 2009). Most recently, it was shown that P. gallaeciensis also produces algicides upon sensing the lignin-derived breakdown product p-coumaric acid from a co-cultivated microalga (Seyedsayamdost et al, 2011).…”

Beneficial effects of 2,4-diacetylphloroglucinol- producing pseudomonads on the marine alga Saccharina latissima

“…Other reports indicated that epiphytic bacteria, which produce bioactive substances, enhanced the fitness of their algal host (Rao et al 2007). We suggest that the metabolites DAPG, MAPG, PLT and rhizoxins act against competitors and degrading or other deleterious microorganisms, like fungal and bacterial pathogens of Saccharina latissima.…”