Antibiotic Production by a Roseobacter Clade-Affiliated Species from the German Wadden Sea and Its Antagonistic Effects on Indigenous Isolates

Abstract

A strain affiliated with the Roseobacter clade and producing a new antibiotic named tropodithietic acid (L. Liang, Ph.D. thesis, University of Göttingen, Göttingen, Germany, 2003) was isolated from the German Wadden Sea. The compound showed strong inhibiting properties with respect to marine bacteria of various taxa and marine algae. Antibiotic production was found to occur during the complete growth phase. Strain mutants without antagonistic properties appeared several times spontaneously.Since the first antibiotic from a marine bacterium was described in 1966 (6), the number of new compounds has increased constantly during the years. Even though only a few compounds from marine organisms might be interesting for the pharmaceutical market today (7), some bacterial species are already used as biocontrols and are added to aquaculture stocks. Most secondary metabolites from marine bacteria found so far were isolated from Streptomyces and Alteromonas species (24). In recent studies wide arrays of marine bacteria were tested for bacterial antagonistic effects, and it was demonstrated that this trait appears to be a widespread feature in marine habitats and present in many bacterial groups (5, 9, 15). Production of secondary metabolites by bacteria of the Roseobacter group has been reported previously (8, 13), and some organisms of this group are thought to be either probiotic or antibiotic in different aquacultures (3,19). Here we describe the antagonistic activity of a new strain of the Roseobacter clade against marine bacteria and algae.A water sample was taken above an intertidal mud flat of the German Wadden Sea (53°42Ј20ЉN, 07°43Ј11ЉE) on 25 October 1999 (water temperature, 9.6°C; pH, 7.9; O 2 saturation, 94%; salinity, 34‰). The sample was taken directly to the laboratory for further processing. Tubes containing 9 ml of marine broth 2216 (Difco) were inoculated with 1 ml of seawater, and the contents were vigorously mixed. Using these tubes, we prepared dilution series with 1:10 steps. The cultures were incubated in the dark at 4, 15, 20, and 28°C (with shaking) for 4 weeks. Growth was determined microscopically and by monitoring turbidity. Aliquots (100 l) from the highest and lowest most-probable-number dilutions of each parallel experiment in which growth was obtained were spread on agar plates with marine agar 2216 (Difco). Plates were incubated at 4, 15, 20, or 28°C in the dark. Different types of colonies obtained were streaked out on fresh plates and transferred at least three times for purification. Bacterial strains were compared by colony morphology and color and by denaturing gradient gel electrophoresis as previously described (23). For a screening of the production of new antimicrobial substances, strains were selected which showed pigmentation or for which no closely related organisms were found by BLAST analysis of their 16S rRNA gene fragments.To detect antimicrobial activity, agar diffusion tests with standard test organisms were performed using Bacillus subtilis and Staphylococcus aureus (bot...

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).…”

Evolutionary Ecology of the Marine Roseobacter Clade

“…The taxonomic distribution of these chemolithotrophic gene sets does not map coherently to species phylogeny, suggesting that gain and loss of these traits have occurred multiple times during Roseobacter evolution, consistent with the scenario that roseobacters have continuously explored new ecological habitats. A few of these ecologically relevant genetic traits, including complete photosynthetic gene clusters (58), capabilities for production of the antibiotic tropodithietic acid (TDA) (59,60), and type IV secretion systems (61), are found on plasmids, suggesting that extrachromosomal DNA could be an important mechanism by which genes useful for environmental adaptation are transferred among roseobacters.…”

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

“…In order to elucidate the pathways leading to TDA synthesis in strain DSM 17395, we conducted transposon insertion mutagenesis and screened for mutants with reduced pigmentation, which was shown to correlate with TDA production (Brinkhoff et al, 2004;Geng et al, 2008;Berger et al, 2011). Within the framework of this study, we identified 26 genes involved in TDA biosynthesis and pigment production, of which 18 are essential ( Table 2).…”