An environmental genomics perspective on the diversity and function of marine sponge-associated microbiota

An Efficient DNA Extraction for a Blue Xestospongia sp. Sponge and Its Associated Microorganisms Containing Cytotoxic Substances

Extraction of high quantity and quality DNAs from marine sponges, which contain diverse and abundant microbial communities, is important to molecular biology techniques for the analysis of nucleic acids. Several marine sponges and their associated microorganisms have been known to produce cytotoxic natural products on several cancer cell lines via DNA damage mechanisms. These marine cytotoxic substances might be one of the factors that cause the low quantity and quality of DNAs during the DNA extraction from its living origin. Therefore, the extraction of DNA of a Thai blue marine sponge Xestospongia sp. with sufficient purity and quantity for molecular study can be challenging. In this study, we developed an efficient extraction method to prepare DNAs from a Thai blue marine sponge Xestospongia sp. which accumulated a highly potent cytotoxic alkaloid with DNA-damaging activity, named Renieramycin M (RM), as a major constituent in high quantity. We demonstrated that removal of RM from the sponge samples by a simple methanolic extraction before DNA extraction dramatically increased the yield and purity of DNAs compared to the RM-unremoved sponge samples. High molecular weight (HMW) genomic DNA was obtained from sponge samples with 8 times of RM elimination by using modified NaOAc salting-out extraction method. The quantity and quality of the prepared DNAs were comparatively determined via spectrophotometry, electrophoresis, and 16S rRNA gene amplification. Our result suggests that the removal of DNA-damaging constituents from the samples is a crucial step and must be seriously taken as the necessary consideration for the practical protocol of DNA extraction.

Characteristic Microbiomes Correlate with Polyphosphate Accumulation of Marine Sponges in South China Sea Areas

Some sponges have been shown to accumulate abundant phosphorus in the form of polyphosphate (polyP) granules even in waters where phosphorus is present at low concentrations. But the polyP accumulation occurring in sponges and their symbiotic bacteria have been little studied. The amounts of polyP exhibited significant differences in twelve sponges from marine environments with high or low dissolved inorganic phosphorus (DIP) concentrations which were quantified by spectral analysis, even though in the same sponge genus, e.g., Mycale sp. or Callyspongia sp. PolyP enrichment rates of sponges in oligotrophic environments were far higher than those in eutrophic environments. Massive polyP granules were observed under confocal microscopy in samples from very low DIP environments. The composition of sponge symbiotic microbes was analyzed by high-throughput sequencing and the corresponding polyphosphate kinase (ppk) genes were detected. Sequence analysis revealed that in the low DIP environment, those sponges with higher polyP content and enrichment rates had relatively higher abundances of cyanobacteria. Mantel tests and canonical correspondence analysis (CCA) examined that the polyP enrichment rate was most strongly correlated with the structure of microbial communities, including genera Synechococcus, Rhodopirellula, Blastopirellula, and Rubripirellula. About 50% of ppk genes obtained from the total DNA of sponge holobionts, had above 80% amino acid sequence similarities to those sequences from Synechococcus. In general, it suggested that sponges employed differentiated strategies towards the use of phosphorus in different nutrient environments and the symbiotic Synechococcus could play a key role in accumulating polyP.

Stable and Enriched Cenarchaeum symbiosum and Uncultured Betaproteobacteria HF1 in the Microbiome of the Mediterranean Sponge Haliclona fulva (Demospongiae: Haplosclerida)

Sponges harbor characteristic microbiomes derived from symbiotic relationships shaping their lifestyle and survival. Haliclona fulva is encrusting marine sponge species dwelling in coralligenous accretions or semidark caves of the Mediterranean Sea and the near Atlantic Ocean. In this work, we characterized the abundance and core microbial community composition found in specimens of H. fulva by means of electron microscopy and 16S amplicon Illumina sequencing. We provide evidence of its low microbial abundance (LMA) nature. We found that the H. fulva core microbiome is dominated by sequences belonging to the orders Nitrosomonadales and Cenarchaeales. Seventy percent of the reads assigned to these phylotypes grouped in a very small number of high-frequency operational taxonomic units, representing niche-specific species Cenarchaeum symbiosum and uncultured Betaproteobacteria HF1, a new eubacterial ribotype variant found in H. fulva. The microbial composition of H. fulva is quite distinct from those reported in sponge species of the same Haliclona genus. We also detected evidence of an excretion/capturing loop between these abundant microorganisms and planktonic microbes by analyzing shifts in seawater planktonic microbial content exposed to healthy sponge specimens maintained in aquaria. Our results suggest that horizontal transmission is very likely the main mechanism for symbionts' acquisition by H. fulva. So far, this is the first shallow water sponge species harboring such a specific and predominant assemblage composed of these eubacterial and archaeal ribotypes. Our data suggests that this symbiotic relationship is very stable over time, indicating that the identified core microbial symbionts may play key roles in the holobiont functioning.

Microbiomes of the Enteropneust, Saccoglossus bromophenolosus, and Associated Marine Intertidal Sediments of Cod Cove, Maine

Enteropneusts are widely distributed marine invertebrates that accumulate high concentrations of halogenated aromatics. Some of these compounds affect benthic biogeochemistery (e.g., denitrification and ammonia oxidation), but little is known about interactions between enteropneusts and their associated microbial communities. Even less is known about enteropneust host-microbe relationships in the digestive tract. More generally, microbial community composition and diversity in intertidal sediments have received little attention. In this study, high throughput sequence analyses of 16S rRNA genes extracted from microbial communities associated with sediment-free whole individuals of Saccoglossus bromophenolosus and freshly excreted S. bromophenolosus gut sediments revealed a potential Spirochaete symbiont that was abundant, present in gut sediment, but absent in other sediments. Relative to surface sediments, gut communities also revealed evidence for selective losses of some groups and blooms of others, especially Colwellia, Photobacterium, Pseudoalteromonas, and Vibrio. After deposition, gut sediment communities rapidly resembled those of surface sediments. Although hierarchical cluster analysis and Linear Discriminant Analysis Effect Size (LEfSe) differentiated among burrow walls of S. bromophenolosus and a polychaete, Alitta virens, as well as between surface and sub-surface sediments, most operational taxonomic units (OTUs) were shared, with differences largely occurring in relative abundances. This suggests that sediment mixing through bioturbation might act to homogenize community composition, while species-specific impacts by infauna might alter local population abundances. Although Cod Cove is a relatively isolated intertidal system, microbial community members included groups with cosmopolitan distributions and roles in sulfur cycling, e.g., Gammaproteobacteria BD7 and Sva0071, as well as novel OTUs representing a large number of phyla.

An Overview on Marine Sponge-Symbiotic Bacteria as Unexhausted Sources for Natural Product Discovery

Microbial symbiotic communities of marine macro-organisms carry functional metabolic profiles different to the ones found terrestrially and within surrounding marine environments. These symbiotic bacteria have increasingly been a focus of microbiologists working in marine environments due to a wide array of reported bioactive compounds of therapeutic importance resulting in various patent registrations. Revelations of symbiont-directed host specific functions and the true nature of host-symbiont interactions, combined with metagenomic advances detecting functional gene clusters, will inevitably open new avenues for identification and discovery of novel bioactive compounds of biotechnological value from marine resources. This review article provides an overview on bioactive marine symbiotic organisms with specific emphasis placed on the sponge-associated ones and invites the international scientific community to contribute towards establishment of in-depth information of the environmental parameters defining selection and acquisition of true symbionts by the host organisms.

Microbial community structure of two freshwater sponges using Illumina MiSeq sequencing revealed high microbial diversity

Sponges are primitive metazoans that are known to harbour diverse and abundant microbes. All over the world attempts are being made to exploit these microbes for their biotechnological potential to produce, bioactive compounds and antimicrobial peptides. However, the majority of the studies are focussed on the marine sponges and studies on the freshwater sponges have been neglected so far. To increase our understanding of the microbial community structure of freshwater sponges, microbiota of two fresh water sponges namely, Eunapius carteri and Corvospongilla lapidosa is explored for the first time using Next Generation Sequencing (NGS) technology. Overall the microbial composition of these sponges comprises of 14 phyla and on an average, more than 2900 OTUs were obtained from C. lapidosa while E. carteri showed 980 OTUs which is higher than OTUs obtained in the marine sponges. Thus, our study showed that, fresh water sponges also posses highly diverse microbial community than previously thought and it is distinct from the marine sponge microbiota. The present study also revealed that microbial community structure of both the sponges is significantly different from each other and their respective water samples. In the present study, we have detected many bacterial lineages belonging to Firmicutes, Actinobacteria, Proteobacteria, Planctomycetes, etc. that are known to produce compounds of biotechnological importance. Overall, this study gives insight into the microbial composition of the freshwater sponges which is highly diverse and needs to be studied further to exploit their biotechnological capabilities.

The role of sponge-bacteria interactions: the sponge Aplysilla rosea challenged by its associated bacterium Streptomyces ACT-52A in a controlled aquarium system

Sponge-associated bacteria play a critical role in sponge biology, metabolism and ecology, but how they interact with their host sponges and the role of these interactions are poorly understood. This study investigated the role of the interaction between the sponge Aplysilla rosea and its associated actinobacterium, Streptomyces ACT-52A, in modifying sponge microbial diversity, metabolite profile and bioactivity. A recently developed experimental approach that exposes sponges to bacteria of interest in a controlled aquarium system was improved by including the capture and analysis of secreted metabolites by the addition of an absorbent resin in the seawater. In a series of controlled aquaria, A. rosea was exposed to Streptomyces ACT-52A at 10⁶ cfu/ml and monitored for up to 360 h. Shifts in microbial communities associated with the sponges occurred within 24 to 48 h after bacterial exposure and continued until 360 h, as revealed by TRFLP. The metabolite profiles of sponge tissues also changed substantially as the microbial community shifted. Control sponges (without added bacteria) and Streptomyces ACT-52A-exposed sponges released different metabolites into the seawater that was captured by the resin. The antibacterial activity of compounds collected from the seawater increased at 96 and 360 h of exposure for the treated sponges compared to the control group due to new compounds being produced and released. Increased antibacterial activity of metabolites from treated sponge tissue was observed only at 360 h, whereas that of control sponge tissue remained unchanged. The results demonstrate that the interaction between sponges and their associated bacteria plays an important role in regulating secondary metabolite production.

Planctomycetes as Novel Source of Bioactive Molecules

Marine environments are a fruitful source of bioactive compounds some of which are the newest leading drugs in medicinal therapeutics. Of particular importance are organisms like sponges and macroalgae and their associated microbiome. Planctomycetes, abundant in macroalgae biofilms, are promising producers of bioactive compounds since they share characteristics, like large genomes and complex life cycles, with the most bioactive bacteria, the Actinobacteria. Furthermore, genome mining revealed the presence of secondary metabolite pathway genes or clusters in 13 analyzed Planctomycetes genomes. In order to assess the antimicrobial production of a large and diverse collection of Planctomycetes isolated from macroalgae from the Portuguese coast, molecular, and bioactivity assays were performed in 40 bacteria from several taxa. Two genes commonly associated with the production of bioactive compounds, nonribosomal peptide synthetases (NRPS), and polyketide synthases (PKS) genes were screened. Molecular analysis revealed that 95% of the planctomycetes potentially have one or both secondary bioactive genes; 85% amplified with PKS-I primers and 55% with NRPS primers. Some of the amplified genes were confirmed to be involved in secondary metabolite pathways. Using bioinformatic tools their biosynthetic pathways were predicted. The secondary metabolite genomic potential of strains LF1, UC8, and FC18 was assessed using in silico analysis of their genomes. Aqueous and organic extracts of the Planctomycetes were evaluated for their antimicrobial activity against an environmental Escherichia coli, E. coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, and a clinical isolate of Candida albicans. The screening assays showed a high number of planctomycetes with bioactive extracts revealing antifungal (43%) and antibacterial (54%) activity against C. albicans and B. subtilis, respectively. Bioactivity was observed in strains from Rhodopirellula lusitana, R. rubra, R. baltica, Roseimaritima ulvae, and Planctomyces brasiliensis. This study confirms the bioactive capacity of Planctomycetes to produce antimicrobial compounds and encourages further studies envisaging molecule isolation and characterization for the possible discovery of new drugs.

Marine Microbial Secondary Metabolites: Pathways, Evolution and Physiological Roles

Microbes produce a huge array of secondary metabolites endowed with important ecological functions. These molecules, which can be catalogued as natural products, have long been exploited in medical fields as antibiotics, anticancer and anti-infective agents. Recent years have seen considerable advances in elucidating natural-product biosynthesis and many drugs used today are natural products or natural-product derivatives. The major contribution to recent knowledge came from application of genomics to secondary metabolism and was facilitated by all relevant genes being organised in a contiguous DNA segment known as gene cluster. Clustering of genes regulating biosynthesis in bacteria is virtually universal. Modular gene clusters can be mixed and matched during evolution to generate structural diversity in natural products. Biosynthesis of many natural products requires the participation of complex molecular machines known as polyketide synthases and non-ribosomal peptide synthetases. Discovery of new evolutionary links between the polyketide synthase and fatty acid synthase pathways may help to understand the selective advantages that led to evolution of secondary-metabolite biosynthesis within bacteria. Secondary metabolites confer selective advantages, either as antibiotics or by providing a chemical language that allows communication among species, with other organisms and their environment. Herewith, we discuss these aspects focusing on the most clinically relevant bioactive molecules, the thiotemplated modular systems that include polyketide synthases, non-ribosomal peptide synthetases and fatty acid synthases. We begin by describing the evolutionary and physiological role of marine natural products, their structural/functional features, mechanisms of action and biosynthesis, then turn to genomic and metagenomic approaches, highlighting how the growing body of information on microbial natural products can be used to address fundamental problems in environmental evolution and biotechnology.

Genomic mining for novel FADH₂-dependent halogenases in marine sponge-associated microbial consortia

Many marine sponges (Porifera) are known to contain large amounts of phylogenetically diverse microorganisms. Sponges are also known for their large arsenal of natural products, many of which are halogenated. In this study, 36 different FADH₂-dependent halogenase gene fragments were amplified from various Caribbean and Mediterranean sponges using newly designed degenerate PCR primers. Four unique halogenase-positive fosmid clones, all containing the highly conserved amino acid motif "GxGxxG", were identified in the microbial metagenome of Aplysina aerophoba. Sequence analysis of one halogenase-bearing fosmid revealed notably two open reading frames with high homologies to efflux and multidrug resistance proteins. Single cell genomic analysis allowed for a taxonomic assignment of the halogenase genes to specific symbiotic lineages. Specifically, the halogenase cluster S1 is predicted to be produced by a deltaproteobacterial symbiont and halogenase cluster S2 by a poribacterial sponge symbiont. An additional halogenase gene is possibly produced by an actinobacterial symbiont of marine sponges. The identification of three novel, phylogenetically, and possibly also functionally distinct halogenase gene clusters indicates that the microbial consortia of sponges are a valuable resource for novel enzymes involved in halogenation reactions.

Evidence of bacteriophage-mediated horizontal transfer of bacterial 16S rRNA genes in the viral metagenome of the marine sponge Hymeniacidon perlevis

Marine sponges have never been directly examined with respect to the presence of viruses or their potential involvement in horizontal gene transfer. Here we demonstrate for the first time, to our knowledge, the presence of viruses in the marine sponge Hymeniacidon perlevis. Moreover, bacterial 16S rDNA was detected in DNA isolated from these viruses, indicating that phage-derived transduction appears to occur in H. perlevis. Phylogenetic analysis revealed that bacterial 16S rDNA isolated from sponge-derived viral and total DNA differed significantly, indicating that not all species are equally involved in transduction.

PKS and NRPS gene clusters from microbial symbiont cells of marine sponges by whole genome amplification

Whole genome amplification (WGA) approaches provide genomic information on single microbial cells and hold great promise for the field of environmental microbiology. Here, the microbial consortia of the marine sponge Aplysina aerophoba were sorted by fluorescence-activated cell sorting (FACS) and then subjected to WGA. A cosmid library was constructed from the WGA product of a sample containing two bacterial cells, one a member of the candidate phylum Poribacteria and one of a sponge-specific clade of Chloroflexi. Library screening led to the genomic characterization of three cosmid clones, encoding a polyketide synthase (PKS), a non-ribosomal peptide synthetase (NRPS) and the Chloroflexi 16S rRNA gene. PCR screening of WGA products from additional, FACS-sorted single bacterial symbiont cells supports the assignment of the Sup-PKS gene to the Poribacteria and the novel NRPS gene to the Chloroflexi. This promising single-cell genomics approach has permitted cloning of entire gene clusters from single microbial cells of known phylogenetic origin and thus provides a sought-after link between phylogeny and function.

Marine drugs from sponge-microbe association--a review

The subject of this review is the biodiversity of marine sponges and associated microbes which have been reported to produce therapeutically important compounds, along with the contextual information on their geographic distribution. Class Demospongiae and the orders Halichondrida, Poecilosclerida and Dictyoceratida are the richest sources of these compounds. Among the microbial associates, members of the bacterial phylum Actinobacteria and fungal division Ascomycota have been identified to be the dominant producers of therapeutics. Though the number of bacterial associates outnumber the fungal associates, the documented potential of fungi to produce clinically active compounds is currently more important than that of bacteria. Interestingly, production of a few identical compounds by entirely different host-microbial associations has been detected in both terrestrial and marine environments. In the Demospongiae, microbial association is highly specific and so to the production of compounds. Besides, persistent production of bioactive compounds has also been encountered in highly specific host-symbiont associations. Though spatial and temporal variations are known to have a marked effect on the quality and quantity of bioactive compounds, only a few studies have covered these dimensions. The need to augment production of these compounds through tissue culture and mariculture has also been stressed. The reviewed database of these compounds is available at www.niobioinformatics.in/drug.php.

Towards commercial production of sponge medicines

Sponges can provide potential drugs against many major world-wide occurring diseases. Despite the high potential of sponge derived drugs no sustainable production method has been developed. Thus far it is not fully understood why, when, where and how these metabolites are produced in sponges. For the near future sea-based sponge culture seems to be the best production method. However, for controlled production in a defined system it is better to develop in vitro production methods, like in vitro sponge culture or even better sponge cell culture, culture methods for symbionts or the transfer of production routes into another host. We still have insufficient information about the background of metabolite production in sponges. Before production methods are developed we should first focus on factors that can induce metabolite production. This could be done in the natural habitat by studying the relation between stress factors (such as predation) and the production of bioactive metabolites. The location of production within the sponge should be identified in order to choose between sponge cell culture and symbiont culture. Alternatively the biosynthetic pathways could be introduced into hosts that can be cultured. For this the biosynthetic pathway of metabolite production should be unraveled, as well as the genes involved. This review discusses the current state of sponge metabolite production and the steps that need to be taken to develop commercial production techniques. The different possible production techniques are also discussed.

Diversity of pufM genes, involved in aerobic anoxygenic photosynthesis, in the bacterial communities associated with colonial ascidians

Ascidians are invertebrate filter feeders widely distributed in benthic marine environments. A total of 14 different ascidian species were collected from the Western Mediterranean and their bacterial communities were analyzed by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene. Results showed that ascidian tissues harbored Bacteria belonging to Gamma- and Alphaproteobacteria classes, some of them phylogenetically related to known aerobic anoxygenic phototrophs (AAPs), such as Roseobacter sp. In addition, hierarchical cluster analysis of DGGE patterns showed a large variability in the bacterial diversity among the different ascidians analyzed, which indicates that they would harbor different bacterial communities. Furthermore, pufM genes, involved in aerobic anoxygenic photosynthesis in marine and freshwater systems, were widely detected within the ascidians analyzed, because nine out of 14 species had pufM genes inside their tissues. The pufM gene was only detected in those specimens that inhabited shallow waters (<77 m of depth). Most pufM gene sequences were very closely related to that of uncultured marine bacteria. Thus, our results suggest that the association of ascidians with bacteria related to AAPs could be a general phenomenon and that ascidian-associated microbiota could use the light that penetrates through the tunic tissue as an energy source.

Biological characterisation of Haliclona (?gellius) sp.: sponge and associated microorganisms

We have characterised the northern Pacific undescribed sponge Haliclona (?gellius) sp. based on rDNA of the sponge and its associated microorganisms. The sponge is closely related to Amphimedon queenslandica from the Great Barrier Reef as the near-complete 18S rDNA sequences of both sponges were identical. The microbial fingerprint of three specimens harvested at different times and of a transplanted specimen was compared to identify stably associated microorganisms. Most bacterial phyla were detected in each sample, but only a few bacterial species were determined to be stably associated with the sponge. A sponge-specific beta- and gamma-Proteobacterium were abundant clones and both of them were present in three of the four specimens analysed. In addition, a Planctomycete and a Crenarchaea were detected in all sponge individuals. Both were closely related to operational taxonomic units that have been found in other sponges, but not exclusively in sponges. Interestingly, also a number of clones that are closely related to intracellular symbionts from insects and amoeba were detected.

Chasing the treasures of the sea - bacterial marine natural products

Bacterial marine natural products are an important source of novel lead structures for drug discovery. The cytotoxic properties of many of these secondary metabolites are of particular interest for the development of new anticancer agents. Tremendous advances in marine molecular biology, genome sequencing, and bioinformatics have paved the way to fully exploit the biomedical potential of marine bacterial products. In addition, unique biosynthetic enzymes discovered from bacteria from the sea have begun to emerge as powerful biocatalysts in medicinal chemistry and total synthesis. The increasingly interdisciplinary field of marine natural product chemistry thus strongly impacts future developments in medicine, chemistry, and biology.

The screening of antimicrobial bacteria with diverse novel nonribosomal peptide synthetase (NRPS) genes from South China sea sponges

Nonribosomal peptide synthetase (NRPS) adenylation (A) domain genes were investigated by polymerase chain reaction for 109 bacteria isolated from four South China Sea sponges, Stelletta tenuis, Halichondria rugosa, Dysidea avara, and Craniella australiensis. Meanwhile, the antimicrobial bioassay of bacteria with NRPS genes were carried out to confirm the screening of NRPS genes. Fifteen bacteria were found to contain NRPS genes and grouped into two phyla Firmicutes (13 of 15) and Proteobacteria (two of 15) according to 16S rDNA sequences. Based on the phylogenetic analysis of the conserved A domain amino acid sequences, most of the NRPS fragments (11 of 15) showed below 70% similarity to their closest relatives suggesting the novelty of these NRPS genes. All of the 15 bacteria with NRPS genes have antimicrobial activities, with most of them exhibiting activity against multiple indicators including fungi and gram-positive and gram-negative bacteria. The different antimicrobial spectra indicate the chemical diversity of biologically active metabolites of sponge-associated bacteria and the possible role of bacterial symbionts in the host's antimicrobial chemical defense. Phylogenetic analysis based on the representative NRPS genes shows high diversity of marine NRPS genes. The combined molecular technique and bioassay strategy will be useful to obtain sponge-associated bacteria with the potential to synthesize bioactive compounds.

Introduction. Ecological immunology

An organism's fitness is critically reliant on its immune system to provide protection against parasites and pathogens. The structure of even simple immune systems is surprisingly complex and clearly will have been moulded by the organism's ecology. The aim of this review and the theme issue is to examine the role of different ecological factors on the evolution of immunity. Here, we will provide a general framework of the field by contextualizing the main ecological factors, including interactions with parasites, other types of biotic as well as abiotic interactions, intraspecific selective constraints (life-history trade-offs, sexual selection) and population genetic processes. We then elaborate the resulting immunological consequences such as the diversity of defence mechanisms (e.g. avoidance behaviour, resistance, tolerance), redundancy and protection against immunopathology, life-history integration of the immune response and shared immunity within a community (e.g. social immunity and microbiota-mediated protection). Our review summarizes the concepts of current importance and directs the reader to promising future research avenues that will deepen our understanding of the defence against parasites and pathogens.

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.

Marine metagenomics: strategies for the discovery of novel enzymes with biotechnological applications from marine environments

Metagenomic based strategies have previously been successfully employed as powerful tools to isolate and identify enzymes with novel biocatalytic activities from the unculturable component of microbial communities from various terrestrial environmental niches. Both sequence based and function based screening approaches have been employed to identify genes encoding novel biocatalytic activities and metabolic pathways from metagenomic libraries. While much of the focus to date has centred on terrestrial based microbial ecosystems, it is clear that the marine environment has enormous microbial biodiversity that remains largely unstudied. Marine microbes are both extremely abundant and diverse; the environments they occupy likewise consist of very diverse niches. As culture-dependent methods have thus far resulted in the isolation of only a tiny percentage of the marine microbiota the application of metagenomic strategies holds great potential to study and exploit the enormous microbial biodiversity which is present within these marine environments.

Cellular origin of dysiherbaine, an excitatory amino acid derived from a marine sponge

The cellular origin of dysiherbaine, a marine-sponge toxin, was investigated immunohistochemically by using an anti-dysiherbaine antibody. Dysiherbaine-like immunoreactivity was found to be localized in spherical cells harbored in the sponge mesohyl. A combination of ribosomal RNA gene (rDNA) analysis and cell-morphology analysis revealed that the spherical cells were Synechocystis cyanobacteria. However, the sponge, identified as Lendenfeldia chondrodes on the basis of its rDNA sequence, appeared to contain two different chemotypes--dysiherbaine-producing (DH+) and nondysiherbaine-producing (DH-)--both of which inhabited the same region. Synechocystis cells in the DH- sponge were not labeled with antibody, although the 16S rDNA gene profile of the cyanobacteria in the DH- sponge was indistinguishable from that of the cyanobacteria in the DH+ sponge. On the basis of these results, we hypothesize that dysiherbaine is a metabolite of certain varieties of endosymbiotic Synechocystis sp.