LuxS affects biofilm maturation and detachment of the periodontopathogenic bacterium Eikenella corrodens

Biofilm Formation in Campylobacter concisus: The Role of the luxS Gene

Campylobacter concisus is a bacterium that inhabits human oral cavities and is an emerging intestinal tract pathogen known to be a biofilm producer and one of the bacterial species found in dental plaque. In this study, biofilms of oral and intestinal C. concisus isolates were phenotypically characterized. The role of the luxS gene, which is linked to the regulation of biofilm formation in other pathogens, was assessed in relation to the pathogenic potential of this bacterium. Biofilm formation capacity was assessed using phenotypic assays. Oral strains were shown to be the highest producers. A luxS mutant was created by inserting a kanamycin cassette within the luxS gene of the highest biofilm-forming isolate. The loss of the polar flagellum was observed with scanning and transmission electron microscopy (SEM and TEM). Furthermore, the luxS mutant exhibited a significant reduction (p < 0.05) in biofilm formation, motility, and its expression of flaB, in addition to the capability to invade intestinal epithelial cells, compared to the parental strain. The study concluded that C. concisus oral isolates are significantly higher biofilm producers than the intestinal isolates and that LuxS plays a role in biofilm formation, invasion, and motility in this bacterium.

Dissecting signal molecule AI-2 mediated biofilm formation and environmental tolerance in Lactobacillus plantarum

Quorum sensing (QS) exists in bacteria to communicate with each other and regulate group behaviors in a cell density-dependent manner, which uses signal molecule autoinducer-2 (AI-2) to intra- and inter-species communication. Effects of exogenous AI-2 on biofilm formation and environmental tolerance in Lactobacillus plantarum are the focus of this review. The responses to the exogenous AI-2 cross multiple physiological metabolic behaviors involving the bacteria growth, morphological characterization, biofilm development, extracellular polysaccharides (EPS) amount and related genes expression as well as the environmental stresses tolerance. The cell surface was smoother in the AI-2 supplemented treatments than without AI-2. Meanwhile, AI-2 had ability to promote the growth and formation of biofilm by increasing the yield of EPS, the main components of biofilm. The changes in lamC and ftsH gene expression point to altered regulation for hydrolysis process of polysaccharides as well as the potential for enhanced biofilm formation. The presence of AI-2 also significantly improved (p < 0.01) the tolerance of bile salts in L. plantarum, but the same results did not appear in acid tolerance. In conclusion, AI-2 supplementation could improve the biofilm formation and bile salts tolerance in L. plantarum, and this effect was likely modulated by facilitating EPS production and suppression polysaccharides hydrolysis.

Clostridioides difficile LuxS mediates inter-bacterial interactions within biofilms

The anaerobic gut pathogen, Clostridioides difficile, forms adherent biofilms that may play an important role in recurrent C. difficile infections. The mechanisms underlying C. difficile community formation and inter-bacterial interactions are nevertheless poorly understood. C. difficile produces AI-2, a quorum sensing molecule that modulates biofilm formation across many bacterial species. We found that a strain defective in LuxS, the enzyme that mediates AI-2 production, is defective in biofilm development in vitro. Transcriptomic analyses of biofilms formed by wild type (WT) and luxS mutant (luxS) strains revealed a downregulation of prophage loci in the luxS mutant biofilms compared to the WT. Detection of phages and eDNA within biofilms may suggest that DNA release by phage-mediated cell lysis contributes to C. difficile biofilm formation. In order to understand if LuxS mediates C. difficile crosstalk with other gut species, C. difficile interactions with a common gut bacterium, Bacteroides fragilis, were studied. We demonstrate that C. difficile growth is significantly reduced when co-cultured with B. fragilis in mixed biofilms. Interestingly, the absence of C. difficile LuxS alleviates the B. fragilis-mediated growth inhibition. Dual species RNA-sequencing analyses from single and mixed biofilms revealed differential modulation of distinct metabolic pathways for C. difficile WT, luxS and B. fragilis upon co-culture, indicating that AI-2 may be involved in induction of selective metabolic responses in B. fragilis. Overall, our data suggest that C. difficile LuxS/AI-2 utilises different mechanisms to mediate formation of single and mixed species communities.

Overexpression of luxS Promotes Stress Resistance and Biofilm Formation of Lactobacillus paraplantarum L-ZS9 by Regulating the Expression of Multiple Genes

Probiotics have evoked great interest in the past years for their beneficial effects. The aim of this study was to investigate whether luxS overexpression promotes the stress resistance of Lactobacillus paraplantarum L-ZS9. Here we show that overexpression of luxS gene increased the production of autoinducer-2 (AI-2, quorum sensing signal molecule) by L. paraplantarum L-ZS9. At the same time, overexpression of luxS promoted heat-, bile salt-resistance and biofilm formation of the strain. RNAseq results indicated that multiple genes encoding transporters, membrane proteins, and transcriptional regulator were regulated by luxS. These results reveal a new role for LuxS in promoting stress resistance and biofilm formation of probiotic starter.

D-Ribose Interferes with Quorum Sensing to Inhibit Biofilm Formation of Lactobacillus paraplantarum L-ZS9

Biofilms help bacteria survive under adverse conditions, and the quorum sensing (QS) system plays an important role in regulating their activities. Quorum sensing inhibitors (QSIs) have great potential to inhibit pathogenic biofilm formation and are considered possible replacements for antibiotics; however, further investigation is required to understand the mechanisms of action of QSIs and to avoid inhibitory effects on beneficial bacteria. Lactobacillus paraplantarum L-ZS9, isolated from fermented sausage, is a bacteriocin-producing bacteria that shows potential to be a probiotic starter. Since exogenous autoinducer-2 (AI-2) promoted biofilm formation of the strain, expression of genes involved in AI-2 production was determined in L. paraplantarum L-ZS9, especially the key gene luxS. D-Ribose was used to inhibit biofilm formation because of its AI-2 inhibitory activity. Twenty-seven differentially expressed proteins were identified by comparative proteomic analysis following D-ribose treatment and were functionally classified into six groups. Real-time quantitative PCR showed that AI-2 had a counteractive effect on transcription of the genes tuf, fba, gap, pgm, nfo, rib, and rpoN. Over-expression of the tuf, fba, gap, pgm, and rpoN genes promoted biofilm formation of L. paraplantarum L-ZS9, while over-expression of the nfo and rib genes inhibited biofilm formation. In conclusion, D-ribose inhibited biofilm formation of L. paraplantarum L-ZS9 by regulating multiple genes involved in the glycolytic pathway, extracellular DNA degradation and transcription, and translation. This research provides a new mechanism of QSI regulation of biofilm formation of Lactobacillus and offers a valuable reference for QSI application in the future.

Biofilm dispersal: multiple elaborate strategies for dissemination of bacteria with unique properties

In most environments, microorganisms evolve in a sessile mode of growth, designated as biofilm, which is characterized by cells embedded in a self-produced extracellular matrix. Although a biofilm is commonly described as a "cozy house" where resident bacteria are protected from aggression, bacteria are able to break their biofilm bonds and escape to colonize new environments. This regulated process is observed in a wide variety of species; it is referred to as biofilm dispersal, and is triggered in response to various environmental and biological signals. The first part of this review reports the main regulatory mechanisms and effectors involved in biofilm dispersal. There is some evidence that dispersal is a necessary step between the persistence of bacteria inside biofilm and their dissemination. In the second part, an overview of the main methods used so far to study the dispersal process and to harvest dispersed bacteria was provided. Then focus was on the properties of the biofilm-dispersed bacteria and the fundamental role of the dispersal process in pathogen dissemination within a host organism. In light of the current body of knowledge, it was suggested that dispersal acts as a potent means of disseminating bacteria with enhanced colonization properties in the surrounding environment.