Production of antimicrobial compounds by marine epibiotic bacteria

The aim of this thesis was to obtain antimicrobial compounds from marine eukaryote-associated bacteria. The unique environment, present on the surfaces of marine eukaryotes, creates conditions that promote and favour the production of bioactive compounds, such as antimicrobials, by giving the producers a clear advantage in the competition for nutrients. This study has demonstrated the abundance of antimicrobial producing bacteria on two marine algae, Delisea pulchra and Ulva australis. Two antimicrobial compounds, violacein and tropodithietic acid (TDA), have been successfully purified and chemically identified from two different bacterial isolates. Moreover, the production of multiple bioactive compounds was observed for both these bacteria.This study also made an attempt to understand the role of the antimicrobial compounds for the producer organisms. Consequently, the effect of violacein on biofilm formation, as well as the possible role of TDA in the defence of both the producer bacterium and the host, have been proposed. The importance of environmental conditions for the expression of bioactive compounds has also been demonstrated, for example, by showing the necessity of high iron concentrations for the production of bioactives in isolates Ul56 and 0245. Notably, despite the absence of a close phylogenetic relationship between these two isolates, they have shown similar trends in terms of production of bioactive compounds. For the first time, this work also described the construction and analysis of a large insert DNA library in E. coli using genomic DNA from a collection of cultured isolates with demonstrated antimicrobial activity. This approach proved to be successful and led to a substantial increase in the positive hit rates in the functional screening of the library, and provided invaluable information concerning the genes, potentially involved not only in the biosynthesis, but also in the processes associated with the production of bioactive compounds, such as transport and resistance