Evidence for acyl homoserine lactone signal production in bacteria associated with marine sponges

Quorum sensing and bacterial biofilms

This review describes the chemistry of the bacterial biofilms including the chemistry of their constituents and signalling compounds that mediate or inhibit the formation of biofilms. Systems are described with special emphasis, in which quorum sensing molecules (autoinducers) trigger the formation of biofilms. In the first instance, N-acyl-L-homoserine lactones (AHLs) are the focus of this review, whereas the inter-species signal known as furanosyl borate diester and peptide autoinducers used by Gram-positive bacteria are not discussed in detail. Since the first discovery of an AHL autoinducer from Vibrio fischeri a large and further increasing number of different AHL structures from Gram-negative bacteria have been identified. This review gives a summary of all known AHL autoinducers and producing bacterial species. A few systems are discussed, where biofilm formation is suppressed by enzymatic degradation of AHL molecules or interference of secondary metabolites from other species with the quorum sensing systems of communicating bacteria. Finally, the multi-channel quorum sensing system, the intracellular downstream processing of the signal, and the resulting response of whole populations including biofilm formation are discussed for the Vibrio genus that has been extensively investigated.

Mini-review: quorum sensing in the marine environment and its relationship to biofouling

Bacterial quorum sensing (QS) is a cell-cell communication and gene regulatory mechanism that allows bacteria to coordinate swarming, biofilm formation, stress resistance, and production of toxins and secondary metabolites in response to threshold concentrations of QS signals that accumulate within a diffusion-limited environment. This review focuses on the role of QS signaling and QS inhibition in marine bacteria by compounds derived from marine organisms. Since the formation of a biofilm is considered to be an initial step in the development of fouling, direct and indirect effects of QS signals and inhibitors on the process of marine biofouling are discussed. Directions for future investigations and QS-related biotechnological applications are highlighted.

Metabolites from symbiotic bacteria

This review describes secondary metabolites that have been shown to be synthesized by symbiotic bacteria, or for which this possibility has been discussed. It includes 365 references.

Diversity and quorum-sensing signal production of Proteobacteria associated with marine sponges

Marine sponges are hosts to diverse and dense bacterial communities and thus provide a potential environment for quorum sensing. Quorum sensing, a key factor in cell-cell communication and bacterial colonization of higher animals, might be involved in the symbiotic interactions between bacteria and their sponge hosts. Given that marine Proteobacteria are known to produce N-acyl homoserine lactone (AHL) signal molecules, we tested the production of AHLs by Alpha- and Gammaproteobacteria isolated from marine sponges Mycale laxissima and Ircinia strobilina and the surrounding water column. We used three different AHL biodetection systems in diffusion assays: Chromobacterium violaceum, Agrobacterium tumefaciens and Sinorhizobium meliloti with optimal sensitivity to short-chain (C4-C6), moderate-chain (C8-C12) and long-chain (>or= C14) AHLs respectively. Thirteen of 23 isolates from M. laxissima and five of 25 isolates from I. strobilina were found to produce AHLs. Signals were detected from two of eight proteobacterial strains from the water column. Thin-layer chromatographic assays based on the A. tumefaciens reporter system were utilized to determine the AHL profiles of the positive isolates. The types and amounts of AHLs synthesized varied considerably among the strains. Small ribosomal rRNA gene sequencing revealed that the AHL-producing alphaproteobacterial isolates were mainly from the Silicibacter-Ruegeria subgroup of the Roseobacter clade. Two-dimensional gel electrophoresis (2DGE)-based proteomic analyses were congruent with phylogenetic relationships but provided higher resolution to differentiate these closely related AHL-producing strains.

Use of real-time qPCR to quantify members of the unculturable heterotrophic bacterial community in a deep sea marine sponge, Vetulina sp

In this report, real-time quantitative PCR (TaqMan qPCR) of the small subunit (SSU) 16S-like rRNA molecule, a universal phylogenetic marker, was used to quantify the relative abundance of individual bacterial members of a diverse, yet mostly unculturable, microbial community from a marine sponge. Molecular phylogenetic analyses of bacterial communities derived from Caribbean Lithistid sponges have shown a wide diversity of microbes that included at least six major subdivisions; however, very little overlap was observed between the culturable and unculturable microbial communities. Based on sequence data of three culture-independent Lithistid-derived representative bacteria, we designed probe/primer sets for TaqMan qPCR to quantitatively characterize selected microbial residents in a Lithistid sponge, Vetulina, metagenome. TaqMan assays included specificity testing, DNA limit of detection analysis, and quantification of specific microbial rRNA sequences such as Nitrospira-like microbes and Actinobacteria up to 172 million copies per microgram per Lithistid sponge metagenome. By contrast, qPCR amplification with probes designed for common previously cultured sponge-associated bacteria in the genera Rheinheimera and Marinomonas and a representative of the CFB group resulted in only minimal detection of the Rheiheimera in total DNA extracted from the sponge. These data verify that a large portion of the microbial community within Lithistid sponges may consist of currently unculturable microorganisms.

Sponge-associated microorganisms: evolution, ecology, and biotechnological potential

Marine sponges often contain diverse and abundant microbial communities, including bacteria, archaea, microalgae, and fungi. In some cases, these microbial associates comprise as much as 40% of the sponge volume and can contribute significantly to host metabolism (e.g., via photosynthesis or nitrogen fixation). We review in detail the diversity of microbes associated with sponges, including extensive 16S rRNA-based phylogenetic analyses which support the previously suggested existence of a sponge-specific microbiota. These analyses provide a suitable vantage point from which to consider the potential evolutionary and ecological ramifications of these widespread, sponge-specific microorganisms. Subsequently, we examine the ecology of sponge-microbe associations, including the establishment and maintenance of these sometimes intimate partnerships, the varied nature of the interactions (ranging from mutualism to host-pathogen relationships), and the broad-scale patterns of symbiont distribution. The ecological and evolutionary importance of sponge-microbe associations is mirrored by their enormous biotechnological potential: marine sponges are among the animal kingdom's most prolific producers of bioactive metabolites, and in at least some cases, the compounds are of microbial rather than sponge origin. We review the status of this important field, outlining the various approaches (e.g., cultivation, cell separation, and metagenomics) which have been employed to access the chemical wealth of sponge-microbe associations.

Presence of acyl-homoserine lactone in subtidal biofilm and the implication in larval behavioral response in the polychaete Hydroides elegans

Quorum sensing (QS) signals have been considered to play important roles in biofilm development and in the attractiveness of biofilms to higher organisms in marine ecosystem. In this study, bacterial QS signalsacylated homoserine lactone derivatives (AHLs) were detected in 2-, 4-, and 6-day-old subtidal biofilms by using AHLs reporter strains. N-dodecanoyl-homoserine lactone (C12-HSL) was identified in 6-day-old biofilm at a concentration of 9.04 microg cm(-minus;2) (3.36 mmol l(-minus;1)). To investigate the possible role of AHLs in the consequent eventlarval settlement of the polychaete Hydroides elegans onto subtidal biofilmsseven biofilm-derived bacteria that effectively induced larval settlement of H. elegans, were screened for AHL production. One of them, the Vibrio sp. UST950701-007, produced N-hexanoyl-homoserine lactone (C6-HSL). Larval settlement bioassay showed that C6-HSL, C12-HSL, and 3-oxo-octanoyl-homoserine lactone (3-oxo-C8-HLS) at certain concentrations induced some initial larval settlement behaviors such as reducing swimming speed, crawling on the bottom. However, these AHLs did not effectively induce larval settlement in comparison to the effective settlement inducer 3-isobutyl-1-methylxanthine. The possible chemokinetic mechanism and indirect effects of AHLs on larval settlement are suggested.

The effect of quorum-sensing blockers on the formation of marine microbial communities and larval attachment

We studied the effect of the quorum-sensing (QS) blockers 5-hydroxy-3[(1R)-1-hydroxypropyl]-4-methylfuran-2(5H)-one (FUR1), (5R)-3,4-dihydroxy-5-[(1S)-1,2-dihydroxyethyl]furan-2(5H)-one (FUR2) and triclosan (TRI) on the formation of bacterial biofilms, and the effect of these biofilms on the larval attachment of the polychaete Hydroides elegans and the bryozoan Bugula neritina. 14-day-old subtidal biofilms were harvested from artificial substrata and were allowed to develop in the laboratory with and without QS blockers. QS blockers inhibited the production of violacein by the QS reporter strain Chromobacterium violaceum CV026 and did not affect the metabolic activity of bacteria in multispecies biofilms. At a concentration of 10(-3) M all three tested compounds inhibited the establishment of microbial communities, but at one of 10(-4) M only FUR2 inhibited establishment. The tested QS blockers caused changes in bacterial density and bacterial community structure, as revealed by terminal restriction fragment length polymorphism and FISH. The groups most affected by QS blockers were Alphaproteobacteria, Gammaproteobacteria and the Cytophagales. Larvae of H. elegans and B. neritina avoided settling on biofilms that had developed in the presence of QS blockers. Our results suggest that QS blockers directly control the formation of multi-species biofilms, and indirectly - by means of biofilm properties - affect larval attachment on these modified biofilms.

A marine Mesorhizobium sp. produces structurally novel long-chain N-acyl-L-homoserine lactones

Our study focused on a Mesorhizobium sp. that is phylogenetically affiliated by 16S rRNA gene sequence to other marine and saline bacteria of this genus. Liquid chromatography-mass spectrometry investigations of the extract obtained from solid-phase extraction of cultures of this bacterium indicated the presence of several N-acyl homoserine lactones (AHLs), with chain lengths of C(10) to C(16). Chromatographic separation of the active bacterial extract yielded extraordinarily large amounts of two unprecedented acylated homoserine lactones, 5-cis-3-oxo-C(12)-homoserine lactone (5-cis-3-oxo-C(12)-HSL) (compound 1) and 5-cis-C(12)-HSL (compound 2). Quorum-sensing activity of compounds 1 and 2 was shown in two different biosensor systems [Escherichia coli MT102(pSB403) and Pseudomonas putida F117(pKR-C12)]. Furthermore, it was shown that both compounds can restore protease and pyoverdin production of an AHL-deficient Pseudomonas aeruginosa PAO1 lasI rhlI double mutant, suggesting that these signal molecules maybe used for intergenus signaling. In conclusion, these data indicate that the quorum-sensing activity of compounds 1 and 2 is modulated by the chain length and functional groups of the acyl moiety. Additionally, compound 1 showed antibacterial and cytotoxic activities.

Discovery of Complex Mixtures of Novel Long-Chain Quorum Sensing Signals in Free-Living and Host-Associated Marine Alphaproteobacteria

More than 100 bacterial isolates from various marine habitats were screened for AHL production by using gfp reporter constructs based on the lasR system of Pseudomonas aeruginosa and the luxR system of Vibrio fischeri. Of the 67 Alphaproteobacteria tested, most of which belonged into the so-called Roseobacter clade, 39 induced fluorescence in either one or both sensor strains up to 103-fold compared to controls. Acylated homoserine lactones were identified by GC-MS analysis and shown to have chain lengths of C8, C10, C13-C16, and C18. One or two double bonds were often present, while a keto or hydroxyl group occurred only rarely in the side chain. Most strains produced several different AHLs. C18-en-HSL and C18-dien-HSL were produced by Dinoroseobacter shibae, an aerobic anoxygenic phototrophic bacterium isolated from dinoflagellates, and are among the longest AHLs found to date. Z7-C14-en-HSL, which has previously been detected in Rhodobacter sphaeroides, was produced by Roseovarius tolerans and Jannaschia helgolandensis. This signal molecule was synthesised and shown to induce a similar response to the culture supernatant in the respective sensor strain. The widespread occurrence of quorum-sensing compounds in marine Alphaproteobacteria, both free-living strains and those associated to eukaryotic algae, points to a great importance of this signalling mechanism for the adaptation of the organisms to their widely different ecological niches.

Production of acylated homoserine lactones byAeromonasandPseudomonasstrains isolated from municipal activated sludge

Up to now, the production and role of N-acyl homoserine lactones (AHLs) in activated sludge have been poorly understood. In this study, cross-feeding assays with the reporter strains Agrobacterium tumefaciens NTL4 and Chromobacterium violaceum CV026 were used to investigate AHL signal production by municipal activated sludge samples. AHL signal production was consistently detected from municipal activated sludge when different samples were incubated on nutrient media. From one municipal activated sludge sample, 10 strains producing AHL-like auto inducers were isolated by an overlay technique. 16S rDNA-based phylogenetic analysis showed that eight of the isolates belonged to Aeromonas spp. and two to Pseudomonas spp. Box-PCR indicated that six of these Aeromonas isolates were different strains and the two Pseudomonas strains were identical. The production of AHL or AHL-like compounds by these strains was confirmed by thin layer chromatography and biosensor overlays. The six different Aeromonas strains were found to produce the same set of AHLs, including N-hexanoyl-L-homoserine lactone. These results may indicate the possible presence of AHLs in municipal activated sludge. The potential roles of AHL in this eco system are briefly discussed.Key words: municipal activated sludge, acylated homoserine lactones, Aeromonas spp., bioaggregates, Pseudomonas spp., AHL biosensors.

Use of solid-phase extraction to enable enhanced detection of acyl homoserine lactones (AHLs) in environmental samples

A challenge for understanding the role of bacterial cell-cell signalling in the environment is the detection of those signals, which are often present in low (nmol L(-1)) concentrations. We describe here a simple purification method, solid-phase extraction (SPE), for increasing the sensitivity of detection for one such group of signals, acyl homoserine lactones (AHLs), in environmental samples. Spiking of dried marine sponge tissue (Stylinos sp.) with AHLs resulted in detection down to 0.01 ppm for 3-oxo-hexanoyl homoserine lactone (3-oxo C6-HSL) and 1 ppm for hexanoyl homoserine lactone (C6-HSL). Compared with liquid extraction methods use of SPE resulted in twofold and tenfold improvements in sensitivity, respectively.