Autoinducer 2 Controls Biofilm Formation in Escherichia coli through a Novel Motility Quorum-Sensing Regulator (MqsR, B3022)

Abstract

The cross-species bacterial communication signal autoinducer 2 (AI-2), produced by the purified enzymes Pfs (nucleosidase) and LuxS (terminal synthase) from S-adenosylhomocysteine, directly increased Escherichia coli biofilm mass 30-fold. Continuous-flow cells coupled with confocal microscopy corroborated these results by showing the addition of AI-2 significantly increased both biofilm mass and thickness and reduced the interstitial space between microcolonies. As expected, the addition of AI-2 to cells which lack the ability to transport AI-2 (lsr null mutant) failed to stimulate biofilm formation. Since the addition of AI-2 increased cell motility through enhanced transcription of five motility genes, we propose that AI-2 stimulates biofilm formation and alters its architecture by stimulating flagellar motion and motility. It was also found that the uncharacterized protein B3022 regulates this AI-2-mediated motility and biofilm phenotype through the two-component motility regulatory system QseBC. Deletion of b3022 abolished motility, which was restored by expressing b3022 in trans. Deletion of b3022 also decreased biofilm formation significantly, relative to the wild-type strain in three media (46 to 74%) in 96-well plates, as well as decreased biomass (8-fold) and substratum coverage (19-fold) in continuous-flow cells with minimal medium (growth rate not altered and biofilm restored by expressing b3022 in trans). Deleting b3022 changed the wild-type biofilm architecture from a thick (54-m) complex structure to one that contained only a few microcolonies. B3022 positively regulates expression of qseBC, flhD, fliA, and motA, since deleting b3022 decreased their transcription by 61-, 25-, 2.4-, and 18-fold, respectively. Transcriptome analysis also revealed that B3022 induces crl (26-fold) and flhCD (8-to 27-fold). Adding AI-2 (6.4 M) increased biofilm formation of wild-type K-12 MG1655 but not that of the isogenic b3022, qseBC, fliA, and motA mutants. Adding AI-2 also increased motA transcription for the wild-type strain but did not stimulate motA transcription for the b3022 and qseB mutants. Together, these results indicate AI-2 induces biofilm formation in E. coli through B3022, which then regulates QseBC and motility; hence, b3022 has been renamed the motility quorum-sensing regulator gene (the mqsR gene).There is an explosive amount of research on biofilms with the ultimate aim of their control (24); however, little is known about the regulation of this complex process of cell attachment leading to exquisite architecture (11). Since 65% of human bacterial infections involve biofilms (31), understanding the genetic basis of biofilm formation to find effective ways to prevent biofilms is important for combating disease and for engineering applications. To this end, we have studied the whole bacterial genome with DNA microarrays by two complementary approaches: studying biofilm gene expression relative to planktonic cells (34, 35) and studying plant-derived biofilm inhibitors that do not alter the bacterial g...

Autoinducer 2 Is Required for Biofilm Growth ofAggregatibacter(Actinobacillus)actinomycetemcomitans

“…Quorum-sensing circuits that detect and respond to acylhomoserine lactone and/or AI-2 have been reported to regulate the biofilm growth of numerous bacterial species (4,8,17,18,29,30,56). However, many oral species do not have the capacity to produce or respond to acylhomoserine lactone signals (15, 51) but do possess luxS and secrete AI-2.…”

“…As a result, AI-2 has been suggested to represent a widely distributed quorum-sensing signal that is recognized by many organisms (39). Inactivation of luxS has been reported to influence a wide variety of cellular processes, including type III secretion (43), cell motility (26,42), the development of biofilms (4,8,17,18,29,30,56), the expression of virulence factors (12,22,28), and iron uptake (11). The signal transduction mechanism that governs the cellular response to AI-2 has been most thoroughly characterized in Vibrio spp.…”

Signals, Regulatory Networks, and Materials That Build and Break Bacterial Biofilms

“…The challenge of the researcher is to determine which of the conditions studied in the lab are relevant to environments experienced by the bacterium in the wild. Conditions such as the nutritional status of the environment and even the presence of conjugative plasmids can lead to quorum-sensing cues being bypassed or overridden (56,105,113,264,267). Presumably, all of these signals feed into intricate cellular signaling networks that ultimately results in the appropriate response to the prevailing conditions.…”

Regulation of autoinducer 2 production and luxS expression in a pathogenic Edwardsiella tarda strain

“…Consistent with its proposed role as an interspecies communication signal, AI-2-mediated signal transduction circuits have been found to regulate biological processes that coordinate the behaviour of cells as a community to best adapt to various environmental situations. Such biological processes include biofilm formation, conjugation, sporulation, and production of virulence elements (Gonzalez Barrios et al, 2006;McNab et al, 2003;Rickard et al, 2006;; the last has been linked to the LuxS/AI-2 quorumsensing system via, most often, mutational studies of the luxS gene (Lyon et al, 2001;Marouni & Sela, 2003;Ohtani et al, 2002;Stroeher et al, 2003;Winzer et al, 2002b;Zhu et al, 2002). been reported to occur in different parts of the world.…”