Abstract
The LuxS enzyme, an S-ribosyl-homocysteine lyase, catalyzes the production of the signal precursor for autoinducer-2 mediated quorum sensing (QS-2) in Vibrio. Its widespread occurrence among bacteria is often considered the evidence for a universal language for interspecies communication. Presence of the luxS gene and production of the autoinducer-2 (AI-2) signal have repeatedly been the only evidences presented to assign a functional QS-2 to the most diverse species. In fact, LuxS has a primary metabolic role as part of the activated methyl cycle. In this review we have analyzed the distribution of QS-2 related genes in Enterobacteriaceae by moving the focus of the investigation from AI-2 production to the detection of potential AI-2 receptors. The latter are common in pathogens or endosymbionts of animals, but were also found in a limited number of Enterobacteriaceae of the genera Enterobacter, Klebsiella, and Pantoea that live in close association with plants or fungi. Although a precise function of QS-2 in these species has not been identified, they all show an endophytic or endosymbiontic lifestyle that suggests a role of type-2 quorum sensing in the adaptation to closed ecosystems.
Highlights
The historical concept of microorganisms as single entities autonomously thriving in their environment has been clearly overcome by abundant evidence demonstrating that many, if not most, bacteria are able to live in organized communities requiring the exchange of some kind of information to coordinate their behavior
It was found in members of the bacterial families Enterobacteriaceae, Pasteurellaceae or Bacillaceae (Bacillus cereus group)
Addition of AI-2 has been associated with regulation of the growth rate in Bacillus anthracis [60] and was shown to negatively affect biofilm formation in B. cereus [61], but definitive experimental evidence that the uptake of AI-2 occurs by the means of LrsB is missing
Summary
The historical concept of microorganisms as single entities autonomously thriving in their environment has been clearly overcome by abundant evidence demonstrating that many, if not most, bacteria are able to live in organized communities requiring the exchange of some kind of information to coordinate their behavior. Many species are able to switch between different lifestyles depending on the environmental conditions met in planta and alter their population structure which may range from a free-living unicellular state to communities of organisms living within extracellular matrices known as biofilms [1] These processes, together with swarming behavior or the production of antibiotics and virulence factors, are often steered by the QS molecules, the so-called autoinducers (AI) [2,3,4]. In bacterial orders other than the Vibrionaceae, the task of detecting a different form of the DPD-derived AI-2 signal, (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), is carried out by an ABC-transporter, the Lsr-receptor complex. We will comb through the published genomes of bacteria and search for elements related to AI-2 signaling that may allow the formulation of bioinformatics-informed predictions on the importance of QS-2, with particular focus on plant-associated Enterobacteriaceae
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