Seasonal Incidence of Autochthonous Antagonistic Roseobacter spp. and Vibrionaceae Strains in a Turbot Larva ( Scophthalmus maximus ) Rearing System

Abstract

Bacteria inhibitory to fish larval pathogenic bacteria were isolated from two turbot larva rearing farms over a 1-year period. Samples were taken from the rearing site, e.g., tank walls, water, and feed for larvae, and bacteria with antagonistic activity against Vibrio anguillarum were isolated using a replica plating assay. Approximately 19,000 colonies were replica plated from marine agar plates, and 341 strains were isolated from colonies causing clearing zones in a layer of V. anguillarum. When tested in a well diffusion agar assay, 173 strains retained the antibacterial activity against V. anguillarum and Vibrio splendidus. Biochemical tests identified 132 strains as Roseobacter spp. and 31 as Vibrionaceae strains. Partial sequencing of the 16S rRNA gene of three strains confirmed the identification as Roseobacter gallaeciensis. Roseobacter spp. were especially isolated in the spring and early summer months. Subtyping of the 132 Roseobacter spp. strains by randomly amplified polymorphic DNA with two primers revealed that the strains formed a very homogeneous group. Hence, it appears that the same subtype was present at both fish farms and persisted during the 1-year survey. This indicates either a common, regular source of the subtype or the possibility that a particular subtype has established itself in some areas of the fish farm. Thirty-one antagonists were identified as Vibrio spp., and 18 of these were V. anguillarum but not serotype O1 or O2. Roseobacter spp. strains were, in particular, isolated from the larval tank walls, and it may be possible to establish an antagonistic, beneficial microflora in the rearing environment of turbot larvae and thereby limit survival of pathogenic bacteria.

Cross-Ocean Distribution of Rhodobacterales Bacteria as Primary Surface Colonizers in Temperate Coastal Marine Waters

“…However, most of them, with the possible exception of the Oceanospirillales species, could not establish stable colonizing populations in the early steps of surface community development, in contrast to the surfacecolonizing Rhodobacterales species. It has been found that certain Roseobacter clade bacteria produce antibacterial compounds when they are growing on a surface, preventing other bacteria, including ␥-Proteobacteria, from colonizing the surface and forming a biofilm (8,10,11,24,44,48). A strain was even found to invade and disperse preestablished biofilms formed by other bacteria (45).…”

“…Once the Roseobacter clade bacterial populations reach a certain density, they may actively expel or take advantage of the other surface-attaching bacteria via quorum-sensing-regulated antibiotic production and other mechanisms (8,10,11,24,35,44,45,48,57). Quorum sensing may also be important for multispecies biofilm formation (22,35,58).…”

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

“…Phaeobacter were found in turbot larva rearings (Hjelm et al, 2004), cutaneous mucus of seahorses (Balcázar et al, 2010) and on cephalopods (Grigioni et al, 2000;Barbieri et al, 2001). In the Chinese Changjiang estuary, close relatives of P. gallaeciensis are among the most abundant bacterial groups (Sekiguchi et al, 2002).…”

Vibrio rhizosphaerae sp. nov., a red-pigmented bacterium that antagonizes phytopathogenic bacteria

“…Some species are found as symbionts in specialized luminous organs of marine fish and invertebrates, whereas a number of other species are well-known pathogens of humans or marine animals (Thompson et al, 2004). To date, relatively few studies have shown that vibrios can produce antimicrobial substances (Hjelm et al, 2004;Long & Azam, 2001;Sugita et al, 1997). However, these vibrios were not identified at the species level.…”