Quorum quenching revisited--from signal decays to signalling confusion

Abstract

In a polymicrobial community, while some bacteria are communicating with neighboring cells (quorum sensing), others are interrupting the communication (quorum quenching), thus creating a constant arms race between intercellular communication. In the past decade, numerous quorum quenching enzymes have been found and initially thought to inactivate the signalling molecules. Though this is widely accepted, the actual roles of these quorum quenching enzymes are now being uncovered. Recent evidence extends the role of quorum quenching to detoxification or metabolism of signalling molecules as food and energy source; this includes "signalling confusion", a term coined in this paper to refer to the phenomenon of non-destructive modification of signalling molecules. While quorum quenching has been explored as a novel anti-infective therapy targeting, quorum sensing evidence begins to show the development of resistance against quorum quenching.

Keywords: N-acylhomoserine lactone; acylase; anti-biofouling; anti-infective; aquaculture; lactonase; oxidoreductase; paraoxonase; quorum quenching resistance; quorum sensing; signalling confusion.

Figure 1.

The signalling molecule N-acyl homoserine lactone (AHL) (1) can be degraded by lactonase, yielding N-acyl homoserine (2). Acylase cleaves the amide bond of AHL by releasing fatty acid (3a) and homoserine lactone (3b). Oxidoreductases from Rhodococcus erythropolis W2 and Burkholderia sp. strain GG4 inactivate AHL by substituting the oxo group at the C3 with hydroxy group (4). Similarly, CYP102A1 from Bacillus megaterium reduces the acyl chain of AHL at the ω-1, ω-2 and ω-3 positions (5a, 5b, 5c). R1 corresponds to the side chain of the C3 position (3-oxo-, 3-hydroxy- and 3-unsubstituted). R2 corresponds to the acyl side chain of AHL and n corresponds to the alkyl group.