The search for new antimicrobial compounds has gained added momentum in recent years, paralleled by the exponential rise in resistance to most known classes of current antibiotics. While modifications of existing drugs have brought some limited clinical success, there remains a critical need for new classes of antimicrobial compound to which key clinical pathogens will be naive. This has provided the context and impetus to marine biodiscovery programmes that seek to isolate and characterize new activities from the aquatic ecosystem. One new antibiotic to emerge from these initiatives is the antibacterial compound tropodithietic acid (TDA). The aim of this study was to provide insight into the bioactivity of and the factors governing the production of TDA in marine Pseudovibrio isolates from a collection of marine sponges. The TDA produced by these Pseudovibrio isolates exhibited potent antimicrobial activity against a broad spectrum of clinical pathogens, while TDA tolerance was frequent in non-TDA producing marine isolates. Comparative genomics analysis suggested a high degree of conservation among the tda biosynthetic clusters while expression studies revealed coordinated regulation of TDA synthesis upon transition from log to stationary phase growth, which was not induced by TDA itself or by the presence of the C10-acyl homoserine lactone quorum sensing signal molecule.

Marine microorganisms continue to be a source of structurally and biologically novel compounds with potential use in the biotechnology industry. The unique physiochemical properties of the marine environment (such as pH, pressure, temperature, osmolarity) and uncommon functional groups (such as isonitrile, dichloroimine, isocyanate, and halogenated functional groups) are frequently found in marine metabolites. These facts have resulted in the production of bioactive substances with different properties than those found in terrestrial habitats. In fact, the marine environment contains a relatively untapped reservoir of bioactivity. Recent advances in genomics, metagenomics, proteomics, combinatorial biosynthesis, synthetic biology, screening methods, expression systems, bioinformatics, and the ever increasing availability of sequenced genomes provides us with more opportunities than ever in the discovery of novel bioactive compounds and biocatalysts. The combination of these advanced techniques with traditional techniques, together with the use of dereplication strategies to eliminate known compounds, provides a powerful tool in the discovery of novel marine bioactive compounds. This review outlines and discusses the emerging strategies for the biodiscovery of these bioactive compounds.

Evidence of bacteriophage-mediated horizontal transfer of bacterial 16S rRNA genes in the viral metagenome of the marine sponge Hymeniacidon perlevis Catriona Harrington, 1,2,3 Antonio Del Casale, 3 Jonathan Kennedy, 1 Horst Neve, 4 Bernard E. Picton, 5 Marlies J. Mooij, 1,2,6 Fergal O'Gara, 1,2,6 Leonid A. Kulakov, 3 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 phagederived 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. INTRODUCTIONViruses are the most numerous and diverse biological entities in not only the marine environment, with 10 6 to 10 9 particles (ml seawater) 21 (Kristensen et al., 2010) and 10 30 unique viral genotypes (Suttle, 2007), but also on Earth (Angly et al., 2006). Viruses are extremely important life forms known to play a crucial role in microbial ecosystems. They are essential for maintaining and influencing the diversity of all microbial communities both by affecting them directly (by controlling numbers of bacterial cells) and by horizontally transferring genetic material to the host via the transduction process (Lohr et al., 2005). Phages can also affect microbial evolution as killing certain dominant bacteria may allow other related strains that are resistant to the phage to become dominant (Angly et al., 2006) in what is known as the 'kill the winner' hypothesis. This may help explain microbial diversity and the changes that can be observed within bacterial community composition ). However, this interaction between phages and their bacterial hosts has remained largely under studied, especially with respect to marine sponge ecosystems.Microbial communities of marine sponges are a major focus of current research, as sponge-associated microbes have been shown to produce a plethora of novel bioactive metabolites (Taylor et al., 2007). Due to the advent of high throughput sequencing, numerous metagenomic studies have facilitated the identification of sponge-associated bacterial groups, which have revealed remarkable levels of bacterial diversity, with 26 major phyla to date having been found to be present in close association with sponge species worldwide (Kennedy et al., 2008;Webster & Taylor 2012;Jackson et al., 2012). Some sponges have a low microbial abundance, with a microbial range similar to that of Abbreviations: CRISPR, clustered regularly interspaced short palindromic repeat; OTU, operational taxonomic unit; TEM, transmission electron microscopy; TFF, tangential flow filtration.The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequences from viral DN...