Transcriptional and Metabolomic Consequences of luxS Inactivation Reveal a Metabolic Rather than Quorum-Sensing Role for LuxS in Lactobacillus reuteri 100-23

Abstract

c Autoinducer-2 (AI-2)-mediated quorum sensing has been extensively studied in relation to the regulation of microbial behavior. There are, however, two potential roles for the AI-2 synthase (LuxS). The first is in the production of AI-2 and the second is as an enzyme in the activated methyl cycle, where it catalyzes the conversion of S-ribosylhomocysteine to homocysteine. The by-product of the reaction catalyzed by LuxS is (S)-4,5-dihydroxy-2,3-pentanedione, which spontaneously forms the furanones known collectively as AI-2. The mammalian gut contains a complex collection of bacterial species so a method of interspecies communication might influence community structure and function. Lactobacillus reuteri 100-23 is an autochthonous inhabitant of the rodent forestomach, where it adheres to the nonsecretory epithelium, forming a biofilm. Microarray comparisons of gene expression profiles of the L. reuteri 100-23 wild type and a luxS mutant under different culture conditions revealed altered transcription of genes encoding proteins associated with cysteine biosynthesis/oxidative stress response, urease activity, and sortasedependent proteins. Metabolomic analysis showed that the luxS mutation affected cellular levels of fermentation products, fatty acids and amino acids. Cell density-dependent changes (log phase versus stationary phase growth) in gene transcription were not detected, indicating that AI-2 was unlikely to be involved in gene regulation mediated by quorum sensing in L. reuteri 100-23.

Stress as a Normal Cue in the Symbiotic Environment

“…The quorum-signaling pheromone AI-2 regulates cellular metabolism and stress responses: e.g., oxidative stress and urease genes are responsive to AI-2 in the gut symbiont Lactobacillus reuteri [74], while AI-2 expressed by the mammalian pathogen Streptococcus pneumoniae regulates expression of biofilm-formation [75]. AI-2 is encoded by diverse microbial taxa, and can also mediate interspecies communication; in fact, AI-2 produced by Ruminococcus obeum, a member of the normal intestinal microbiota, inhibits the transcription of colonization factors encoded by pathogenic Vibrio cholerae , thereby mitigating virulence of this intestinal pathogen in the mouse gut [76].…”

Novel two-component regulatory systems play a role in biofilm formation of Lactobacillus reuteri rodent isolate 100-23

“…Disruption of msrB impairs colonization of mice by L. reuteri (Walter et al, 2005). Disruption of luxS in L. reuteri 100-23 is associated with the metabolic conversion of Sribosyl homocysteine to homocysteine, but not AI-2 quorum-sensing regulation (Wilson et al, 2012). Genes gadB (Su et al, 2011) and dltA increase the acid resistance of L. reuteri.…”

Lactobacillus reuteri 100-23 Modulates Urea Hydrolysis in the Murine Stomach

“…The aaUTP-labeled aRNA was hybridized to a custom-designed Agilent microarray specific for L. reuteri 100-23 (GEO accession number GPL10986, series number GSE36286). Details of the microarray hybridization are as described previously (9). Microarrays were scanned at 5 m using a GenePix 400B scanner (photomultiplier [PMT] settings, 780 for red channel and 510 for green channel; Axon Instruments) and GenePix Pro (version 6.0) software.…”

“…Our recent study with strain 100-23 used microarray and metabolomic comparisons of the wild type (WT) and a luxS mutant derivative to determine altered gene transcriptions and the resulting metabolic consequences to the bacteria (9). We now aim to extend knowledge of the ecological effects of colonization of the mouse stomach by strain 100-23 initiated through a microarray screen of Lactobacillus gene transcription.…”