355
(d) Modification of acyl chain: AHL oxidase and reductase: Acyl chain modification was reported only in bacteria. The first AHL oxido-reductase activity was
reported in a strain of Rhodocuccus erythropolis (Uroz et al. 2005; Tay and Yew
2013). P450 monooxygenase is an AHLase obtained from Bacillus megaterium, which oxidizes fatty acids and N-fatty acyl amino acids. Here the AHL
molecules are not degraded, instead there occurs a modification in the structure
of the signal and this modification might play a role in the regulation of QSrelated functions (Chowdhary et al. 2007; Uroz et al. 2009).
14.4 Sources of Quorum Quenching Inhibitors
14.4.1 Natural Quorum Sensing Inhibitors
Numerous substances have been evaluated for their ability to interfere with
QS. Quorum sensing inhibitors which are isolated from natural products are excellent resources for developing powerful antivirulence drugs. Plants and fungi have
coexisted with QS bacteria for millions of years and some of them are expected to
produce quorum quenching compounds. Penicillium sp. found to produce secondary metabolites with quorum quenching ability. Two of these compounds which
have been identified are patulin and penicillic acid (PA) which target Rh1R and Las
R quorum sensing regulators, respectively. Algal-derived brominated furanones
especially from the Delisea pulchra have been found to exhibit quorum quenching
activity. Their quorum sensing effect may be attributed to conformational changes
which occur due to the binding of blockers to the receptors which ultimately leads
to destabilization of the receptor. By intervening with QS-controlled motility they
prevent bacterial colonization and macrofouling. Serratia liquefaciens MG1 is one
such example of inhibition of swarming motility by halogenated furanones (Adak
et al. 2011; Kjelleberg et al. 1997).
14.4.1.1 Quorum Quenching Compounds from Terrestrial Sources
Natural products, especially plants, have been explored mostly for their therapeutic
uses in traditional medicine; plant-derived biologically active constituents have led
to the discovery of new drugs which have been used for the treatment of various
ailments (Hanson 2003; Koh et al. 2013), but now the research has shifted from this
to their ecological role in regulating interactions between the microorganisms.
Plants as we know lack of advanced immune systems like humans and other mammals are possessing, so, instead of relying on biochemical and cellular defense systems, plants may have evolved to produce quorum quenching compounds
(antiquorum sensing compounds) that can be employed to overcome quorum sensing pathogens that invade plants (Koh et al. 2013). Some plants have been found to
produce chemicals which are capable of interfering with bacterial quorum sensing.
These plants include Daucus carota subsp. sativus (carrot), Solanum lycopersicum
(tomato), Glycine max (soyabean), Capsicum chinense (chili), Nymphaea (water
lily), Pisum sativum (pea), and Allium sativum (garlic) (Adak et al. 2011). Eukaryotes
have evolved a more efficient way to manipulate bacterial quorum sensing system
14 Quorum Quenching Compounds from Natural Sources
(d) Modification of acyl chain: AHL oxidase and reductase: Acyl chain modification was reported only in bacteria. The first AHL oxido-reductase activity was
reported in a strain of Rhodocuccus erythropolis (Uroz et al. 2005; Tay and Yew
2013). P450 monooxygenase is an AHLase obtained from Bacillus megaterium, which oxidizes fatty acids and N-fatty acyl amino acids. Here the AHL
molecules are not degraded, instead there occurs a modification in the structure
of the signal and this modification might play a role in the regulation of QSrelated functions (Chowdhary et al. 2007; Uroz et al. 2009).
14.4 Sources of Quorum Quenching Inhibitors
14.4.1 Natural Quorum Sensing Inhibitors
Numerous substances have been evaluated for their ability to interfere with
QS. Quorum sensing inhibitors which are isolated from natural products are excellent resources for developing powerful antivirulence drugs. Plants and fungi have
coexisted with QS bacteria for millions of years and some of them are expected to
produce quorum quenching compounds. Penicillium sp. found to produce secondary metabolites with quorum quenching ability. Two of these compounds which
have been identified are patulin and penicillic acid (PA) which target Rh1R and Las
R quorum sensing regulators, respectively. Algal-derived brominated furanones
especially from the Delisea pulchra have been found to exhibit quorum quenching
activity. Their quorum sensing effect may be attributed to conformational changes
which occur due to the binding of blockers to the receptors which ultimately leads
to destabilization of the receptor. By intervening with QS-controlled motility they
prevent bacterial colonization and macrofouling. Serratia liquefaciens MG1 is one
such example of inhibition of swarming motility by halogenated furanones (Adak
et al. 2011; Kjelleberg et al. 1997).
14.4.1.1 Quorum Quenching Compounds from Terrestrial Sources
Natural products, especially plants, have been explored mostly for their therapeutic
uses in traditional medicine; plant-derived biologically active constituents have led
to the discovery of new drugs which have been used for the treatment of various
ailments (Hanson 2003; Koh et al. 2013), but now the research has shifted from this
to their ecological role in regulating interactions between the microorganisms.
Plants as we know lack of advanced immune systems like humans and other mammals are possessing, so, instead of relying on biochemical and cellular defense systems, plants may have evolved to produce quorum quenching compounds
(antiquorum sensing compounds) that can be employed to overcome quorum sensing pathogens that invade plants (Koh et al. 2013). Some plants have been found to
produce chemicals which are capable of interfering with bacterial quorum sensing.
These plants include Daucus carota subsp. sativus (carrot), Solanum lycopersicum
(tomato), Glycine max (soyabean), Capsicum chinense (chili), Nymphaea (water
lily), Pisum sativum (pea), and Allium sativum (garlic) (Adak et al. 2011). Eukaryotes
have evolved a more efficient way to manipulate bacterial quorum sensing system
14 Quorum Quenching Compounds from Natural Sources