Quorum sensing signal production by sponge-associated bacteria isolated from the Red Sea, Egypt

Bacteria regulate their social activities and physiological processes through a quorum sensing (QS) mechanism. Many bacteria inhabit the mesohyl matrix of sponges. This symbiotic relationship is believed to contribute to the health and nutrition of sponges by production of protective antibiotics, the acquisition of limiting nutrients and nitrogen fixation. Marine isolates were analysed by bioassays using two different acylated homoserine lactone (AHL) reporter bacteria Chromobacterium violaceum 026 (CV026) and Agrobacterium tumefaciens KYC55. Thirty four marine isolates activated the A. tumefaciens and produce blue color. Using degenerate LuxS primers, partial LuxS gene sequences were detected in both Gram-negative and Gram-positive species including Bacillus species, Proteus species, uncultured Bacterium species, Micrococcus species and Bacterium NLAE-zl-H221. Using degenerate LuxR primers, partial LuxR gene sequences were detected in Proteus spp., Providencia species and Bacterium NLAE-zl-H221. Partial LuxS gene sequences were detected in both Gram-negative and Gram-positive. The results thus assure the fact that LuxS gene has been proposed to be a universal interspecies signaling molecule. This study showed that, Proteus mirabilis strain SZH18, Proteus vulgaris and Bacterium NLAE-zl-H221 have both luxS and luxR genes, thus it was claimed that these isolates have the potential to use two different QS systems, for intraspecies communication and communication with other species. Key words: Quorum sensing, autoinducers, biofilm, double layer method, quorum quenching, N-acyl homoserine lactones.