Antagonism of bacterial cell to cell signalling by metabolites of marine gram-positive bacteria

A form of communication in bacteria called quorum sensing (QS) regulates both microbial biofilm development and pathogenesis. QS is a process by which bacteria take a census of their numbers and regulate specific phenotypic expression using small signaling molecules called autoinducers. Interference with QS has been identified as a potentially novel therapeutic approach to the treatment of bacterial infections. This attenuation of the bacterial community prevents the successful establishment of an infection. The second chapter discusses the isolation of causative agents of bioluminescence inhibition in Vibrio harveyi. Bioassay-guided fractionation lead to the isolation of two arylethylamides from isolate C42, a Halobacillus salinus. The bioactive agents were able to inhibit the quorum sensing systems of two other bacteria, Chromobacterium violaceum and Escherichia coli. Studies indicated that the compounds are competitive inhibitors of V. harveyi LuxR expression. Following the isolation of these compounds, structure activity relationships were probed as explained in chapter three. Although none of the synthetic analogues were capable of inhibiting all three quorum sensing systems of the reporter strains, at a similar or lower concentration as the natural metabolite, several had increased potency against one or two assay strains. In chapter four, 332 Gram-positive bacterial isolates from a broad range of marine environments and substrata were screened for inhibition of the quorum-sensing controlled phenotype of bioluminescence in the marine bacterium V. harveyi BB120. Two assay methods were designed to test for the inhibition of Vibrio harveyi bioluminescence by environmental strains. Of the isolate panel, 49 isolates interfered with bioluminescence, and chemical extracts from 28 reproduced the observed activity. Chemical analysis of one of the active isolates, Bacillus cereus isolate D28, lead to the isolation and identification of cyclic-L-proline-L-tyrosine as an antagonist of bioluminescence production by V. harveyi. Chapter five focuses on microbe-microbe interactions from marine particles, hotspots for bacterial colonization. Using the two assays developed in the previous chapter, isolates from particles and the surrounding water column were assayed for the production of both toxic and non-toxic substances. Results from these studies suggest that non-toxic interactions are more prevelant amongst in all bacterial types than toxic interactions