Abstract
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.
Highlights
Quorum sensing (QS) is a term created to describe an environmental sensing system that allows bacteria to monitor their population density (Nealson et al, 1979; Fuqua et al, 1994)
This study showed that, Proteus mirabilis strain SZH18, Proteus vulgaris and Bacterium NLAE-zl-H221 have both luxS and luxR genes, it was claimed that these isolates have the potential to use two different quorum sensing (QS) systems, for intraspecies communication and communication with other species
Eighteen bacterial isolates with distinct morphological appearance were taken as a representative samples from a total of 66 isolates to be identified by 16S rDNA sequence analysis, using the BLASTn tool of the National Center of Biotechnology Information (NCBI) (Table 2)
Summary
Quorum sensing (QS) is a term created to describe an environmental sensing system that allows bacteria to monitor their population density (Nealson et al, 1979; Fuqua et al, 1994). It is obvious that many bacteria regulate their social activities and physiological processes through a quorum sensing mechanism, including symbiosis, formation of spore or fruiting bodies, bacteriocin production, genetic competence, programmed cell death and virulence. Quorum sensing mechanism can be divided into at least 4 steps: (1) creation of signal molecules by bacteria;. (2) the bacteria release these signaling molecules into the neighboring environment; (3) specific receptors recognize these signaling molecules, once they exceed a threshold concentration, resulting in four changes in gene regulation (Sifri, 2008; Galloway et al, 2010). Up on QS induction of gene expression, the synthesis of proteins involved in the signal molecule production is increased, thereby augmenting the synthesis of the signal molecule that results in a positive feedback loop. That is why QS are called autoinducers (AIs) (Sifri, 2008)
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