• biologia

The marine environment shows a vast ecological, chemical, and biological diversity, from unicellular microorganisms to vertebrates, with more than 300 000 described species of plants and animals. Marine microorganisms are frequently members of complex communities in which competition for limited space and resources can be strong. Marine bacteria represent an emerging source of natural products as they produce a variety of structurally diverse and biologically active secondary metabolites. Nevertheless, the ecological role of these small molecules is not entirely understood. Secondary metabolites from marine bacteria take part in a variety of processes including nutrient acquisition, chemical communication and competition. The importance of these secondary metabolites in the control of infectious and parasitic organisms has been largely overlooked for many years. The overall aim of this work is to contribute to the discovery of novel marine bioactive compounds obtained from bacterial communities that display antagonistic biological activity. This involved the use of the nematode Caenorhabditis elegans (C.elegans) as a model system to detect and identify bioactive bacterial compounds that target multicellular eukaryotes. C. elegans is a free –living terrestrial nematode that feeds on bacteria, and can be easily grown and manipulated under laboratory conditions. Previous work isolated bacterial DNA from the seaweed Ulva australis (U.australis) and identified some genetic elements displaying bioactivity when expressed in the heterologous Escherichia. coli (E.coli) host. This work expands upon the previous identification of environmental DNA encoding bioactive compounds by performing toxicity tests to identify the most toxic clone (i.e., JJ117) that was most detrimental towards C. elegans. A random transposon mutant library of JJ17 was then obtained and screened for a loss of toxicity towards C. elegans. Loss of nematocidal activity for 13 selected clones was then further characterised via a toxicity assay. Finally Tn-sequencing was attempted to identify the specific genetic elements in these clones that are responsible for the toxic activity. This project suggests that marine microorganisms are a source of bioactivity against the nematode C. elegans, and that these bacterial secondary metabolites likely play a role in the complex ecology of the marine environment.