Using functional screening of marine metagenomic libraries for anti- quorum sensing compounds as a platform for microbial ecology study and drug discovery

Quorum Sensing (QS) is a cell-to-cell communication which relies on the production of signaling molecules according to cell density and growth stage. These molecules enable the synchronization of gene expression, resulting in different community functions, particularly virulence. QS affects bacterial acclimation to environment changes, bioluminescence, virulence, symbiosis, antibiotic production, swarming and swimming motility, biofilm formation and conjugation. The best characterized QS system among gram-negative bacteria, rely on Acylated Homoserine Lactone (AHL). The marine environment is dominated by microorganisms with high metabolic activity. Therefore this environment may hold a source for the discovery of microorganisms with unidentified genes involved in inter-cell communication such as quorum sensing. Traditional culturing techniques have led to identification of less than 1% of all microbes. The emergence of metagenomic techniques has allowed access to information regarding biochemical pathways characterizing these unknown microorganisms. To ascertain which communication pathways these microorganisms rely on, we evaluated the QS inhibition characteristics of some of these unknowns. Over 6000 environmental Bacterial Artificial Chromosome (BAC) clones from the Red and Mediterranean Sea metagenomic library were screened using indicator bacteria Chromobacterium violaceum. This screening method allowed the identification of QS inhibition ability and indicated that it is common in the marine environment. We used biofilm forming bacteria models P. aeruginosa to successfully identify molecules that play a role in QS inhibition and anti-biofilm ability. Sequencing the BACs edges in these active clones revealed that among others, Synechococcusis a key player. Thus such functional screening provides a powerful tool in the discovery of functional metabolites resulting in a better understanding of microbial diversity.