Acyl homoserine lactone changes the abundance of proteins and the levels of organic acids associated with stationary phase in Salmonella Enteritidis

Regulation of extracellular polymers based on quorum sensing in wastewater biological treatment from mechanisms to applications: A critical review

Extracellular polymeric substances (EPS) regulated by quorum sensing (QS) could directly mediate adhesion between microorganisms and form tight microbial aggregates. Besides, EPS have redox properties, which can facilitate electron transfer for promoting electroactive bacteria. Currently, the applications research on improving wastewater biological treatment performance based on QS regulated EPS have been widely reported, but reviews on the level of QS regulated EPS to enhance EPS function in microbial systems are still lacking. This work proposes the potential mechanisms of EPS synthesis by QS regulation from the viewpoint of material metabolism and energy metabolism, and summarizes the effects of QS on EPS synthesis. By synthesizing the role of QS in EPS regulation, we further point out the applications of QS-regulated EPS in wastewater biological treatment, which involve a series of aspects such as strengthening microbial colonization, mitigating membrane biofouling, improving the shock resistance of microbial metabolic systems, and strengthening the electron transfer capacity of microbial metabolic systems. According to this comprehensive review, future research on QS-regulated EPS should focus on the exploration of the micro-mechanisms, and economic regulation strategies for QS-regulated EPS should be developed, while the stability of QS-regulated EPS in long-term production experimental research should be further demonstrated.

Furanone and phytol influence metabolic phenotypes regulated by acyl-homoserine lactone in Salmonella

Salmonella is an important foodborne pathogen, and it is unable to produce the quorum sensing signaling molecules called acyl-homoserine lactones (AHLs). However, it synthesizes the SdiA protein, detecting AHL molecules, also known as autoinducer-1 (AI-1), in the external environment. Exogenous AHLs can regulate specific genes related to virulence and stress response in Salmonella. Thus, interfering with quorum sensing can be a strategy to reduce virulence and help elucidate the cell-to-cell communication role in the pathogens' response to extracellular signals. This study aimed to evaluate the influence of the quorum sensing inhibitors furanone and phytol on phenotypes regulated by N-dodecanoyl homoserine lactone (C12-HSL) in Salmonella enterica serovar Enteritidis. The furanone C30 at 50 nM and phytol at 2 mM canceled the alterations promoted by C12-HSL on glucose consumption and the levels of free cellular thiol in Salmonella Enteritidis PT4 578 under anaerobic conditions. In silico analysis suggests that these compounds can bind to the SdiA protein of Salmonella Enteritidis and accommodate in the AHL binding pocket. Thus, furanone C30 and phytol act as antagonists of AI-1 and are likely inhibitors of the quorum sensing mechanism mediated by AHL in Salmonella.

Comparative Proteomic Analyses Between Biofilm-Forming and Non-biofilm-Forming Strains of Corynebacterium pseudotuberculosis Isolated From Goats

Caseous lymphadenitis (CLA) is a chronic disease that affects small ruminants and causes economic losses in the associated breeding system. The causative agent of CLA is Corynebacterium pseudotuberculosis, a Gram-positive bacterium that exhibits tropism for external and internal lymph nodes and induces abscess formation in the host. Bacterial communities often produce a biofilm matrix that serves various functions, including protection against hostile environmental conditions, antibiotics, and the host immune response. Although biofilm formation has been reported for C. pseudotuberculosis, not all strains demonstrate this property in culture. In this work, we report the first comparative proteomic analysis of one biofilm-forming (CAPJ4) and one biofilm-non-forming strain (CAP3W) of C. pseudotuberculosis isolated from goats. Bacterial whole cell protein extracts were obtained for mass spectrometry analyses. Using LC-MS/MS, our studies reveal three and four proteins exclusively found in the CAPJ4 and CAP3W proteome, respectively. In addition, label-free quantitative analysis identified 40 proteins showing at-least 2-fold higher values in CAPJ4 compared CAP3W proteome Notably, CAPJ4 differentially synthesized the penicillin-binding protein, which participates in the formation of peptidoglycans. CAPJ4 also exhibited upregulation of N-acetylmuramoyl-L-alanine amidase and galactose-1-phosphate uridylyltransferase, which are involved in biofilm formation and exopolysaccharide biosynthesis. Here, we demonstrate that biofilm formation in C. pseudotuberculosis is likely associated with specific proteins, some of which were previously shown to be associated with virulence and biofilm formation in other organisms. Our findings may drive studies related to the bacterial mechanisms involved in the biofilm formation, in addition to providing targets for the treatment of CLA.

The virulence of Salmonella Enteritidis in Galleria mellonella is improved by N-dodecanoyl-homoserine lactone

Salmonella is a food and waterborne pathogen responsible for outbreaks worldwide, and it can survive during passage through the stomach and inside host phagocytic cells. Virulence genes are required for infection and survival in macrophages, and some are under the regulation of the quorum sensing (QS) system. This study investigated the influence of the autoinducer 1 (AI-1), N-dodecanoyl-homoserine lactone (C12-HSL), on the virulence of Salmonella PT4 using Galleria mellonella as an infection model. Salmonella PT4 was grown in the presence and absence of C12-HSL under anaerobic conditions for 7 h, and the expression of rpoS, arcA, arcB, and invA genes was evaluated. After the inoculation of G. mellonella with the median lethal dose (LD₅₀) of Salmonella PT4, the survival of bacteria inside the larvae and their health status (health index scoring) were monitored, as well as the pigment, nitric oxide (NO), superoxide dismutase (SOD), and catalase (CAT) production. Also, the hemocyte viability, the induction of caspase-3, and microtubule-associated light chain 3 (LC3) protein in hemocytes were evaluated. Salmonella PT4 growing in the presence of C12-HSL showed increased rpoS, arcA, arcB, and invA expression and promoted higher larvae mortality and worse state of health after 24 h of infection. The C12-HSL also increased the persistence of Salmonella PT4 in the hemolymph and in the hemocytes. The highest pigmentation, NO production, and antioxidant enzymes were verified in the larva hemolymph infected with Salmonella PT4 grown with C12-HSL. Hemocytes from larvae infected with Salmonella PT4 grown with C12-HSL showed lower viability and higher production of caspase-3 and LC3. Taken together, these findings suggest that C12-HSL could be involved in the virulence of Salmonella PT4.

Salmonella enterica Optimizes Metabolism After Addition of Acyl-Homoserine Lactone Under Anaerobic Conditions

Acyl-homoserine lactones (AHLs) are quorum sensing (QS) signaling molecules that mediate cell-to-cell communication in Gram-negative bacteria. Salmonella does not produce AHL, however, it can recognize AHLs produced by other species through SdiA protein modulating important cellular functions. In this work, the influence of the N-dodecanoyl-DL-homoserine lactone (C12-HSL) on glucose consumption, metabolic profile, and gene expression of Salmonella throughout the cultivation time in Tryptic Soy Broth (TSB) under anaerobic conditions was evaluated. Analysis of the supernatant culture in high-performance liquid chromatography (HPLC) revealed lower glucose uptake after 4 and 6 h of the addition of C12-HSL. Gas chromatography-mass spectrometry (GC-MS) based analysis of the intracellular metabolites revealed C12-HSL perturbation in the abundance levels of metabolites related to the metabolic pathways of glycerolipids, purines, amino acids, and aminoacyl-tRNA biosynthesis. The real-time quantitative PCR (RT-qPCR) indicated that Salmonella increase expression of genes associated with nucleoside degradation and quantification of metabolites supported the induction of pentose phosphate pathway to ensure growth under lower glucose consumption. The obtained data suggest an important role of C12-HSL in the optimization of metabolism at a situation of high population densities.

Nisin and acid resistance in Salmonella is enhanced by N-dodecanoyl-homoserine lactone

Salmonella is a foodborne pathogen that can develop resistance to different stresses, which is essential for successful infection of the host. Some genes directly related to acid resistance are also involved in cationic peptide resistance in Gram-negative bacteria and could be under the control of quorum sensing (QS) mediated by autoinducer 1, known as acyl-homoserine lactone. Here, we investigated the influence of autoinducer 1, N-dodecanoyl-homoserine lactone (C12-HSL) on the resistance of Salmonella enterica subspecies enterica serovar Enteritidis to nisin and acid stress. Salmonella cells growing in anaerobic tryptic soy agar (TSB) at a pH of 7.0 for 7 h were submitted to acid stress at a pH of 4.5 in the presence and absence of nisin and were either supplemented or not with C12-HSL. Viable cell counts, gene expression, membrane charge alterations, fatty acid composition, and intracellular content leakage were observed. The autoinducer C12-HSL increased nisin resistance and survival at a pH of 4.5 in Salmonella. Also, C12-HSL increased the expression of the genes, phoP, phoQ, pmrA, and pmrB, which are involved with antimicrobial and acid resistance. The positive charge on the cell surface and concentration of cyclopropane fatty acid of the cellular membrane were increased in the presence of C12-HSL under acidic conditions, whereas membrane fluidity decreased. The loss of K⁺ and NADPH, promoted by nisin, was reduced in the presence of C12-HSL at a pH of 4.5. Taken together, these findings suggest that quorum sensing plays an important role in enhanced nisin and acid resistance in Salmonella.

Identification of common highly expressed genes of Salmonella Enteritidis by in silico prediction of gene expression and in vitro transcriptomic analysis

Chickens are the reservoir host of Salmonella Enteritidis. Salmonella Enteritidis colonizes the gastro-intestinal tract of chickens and replicates within macrophages without causing clinically discernable illness. Persistence of S. Enteritidis in the hostile environments of intestinal tract and macrophages allows it to disseminate extra-intestinally to liver, spleen, and reproductive tract. Extra-intestinal dissemination into reproductive tract leads to contamination of internal contents of eggs, which is a major risk factor for human infection. Understanding the genes that contribute to S. Enteritidis persistence in the chicken host is central to elucidate the genetic basis of the unique pathobiology of this public health pathogen. The aim of this study was to identify a succinct set of genes associated with infection-relevant in vitro environments to provide a rational foundation for subsequent biologically-relevant research. We used in silico prediction of gene expression and RNA-seq technology to identify a core set of 73 S. Enteritidis genes that are consistently highly expressed in multiple S. Enteritidis strains cultured at avian physiologic temperature under conditions that represent intestinal and intracellular environments. These common highly expressed (CHX) genes encode proteins involved in bacterial metabolism, protein synthesis, cell-envelope biogenesis, stress response, and a few proteins with uncharacterized functions. Further studies are needed to dissect the contribution of these CHX genes to the pathobiology of S. Enteritidis in the avian host. Several of the CHX genes could serve as promising targets for studies towards the development of immunoprophylactic and novel therapeutic strategies to prevent colonization of chickens and their environment with S. Enteritidis.

N-dodecanoyl-homoserine lactone influences the levels of thiol and proteins related to oxidation-reduction process in Salmonella

Quorum sensing is a cell-cell communication mechanism mediated by chemical signals that leads to differential gene expression in response to high population density. Salmonella is unable to synthesize the autoinducer-1 (AI-1), N-acyl homoserine lactone (AHL), but is able to recognize AHLs produced by other microorganisms through SdiA protein. This study aimed to evaluate the fatty acid and protein profiles of Salmonella enterica serovar Enteritidis PT4 578 throughout time of cultivation in the presence of AHL. The presence of N-dodecanoyl-homoserine lactone (C12-HSL) altered the fatty acid and protein profiles of Salmonella cultivated during 4, 6, 7, 12 and 36 h in anaerobic condition. The profiles of Salmonella Enteritidis at logarithmic phase of growth (4 h of cultivation), in the presence of C12-HSL, were similar to those of cells at late stationary phase (36 h). In addition, there was less variation in both protein and fatty acid profiles along growth, suggesting that this quorum sensing signal anticipated a stationary phase response. The presence of C12-HSL increased the abundance of thiol related proteins such as Tpx, Q7CR42, Q8ZP25, YfgD, AhpC, NfsB, YdhD and TrxA, as well as the levels of free cellular thiol after 6 h of cultivation, suggesting that these cells have greater potential to resist oxidative stress. Additionally, the LuxS protein which synthesizes the AI-2 signaling molecule was differentially abundant in the presence of C12-HSL. The NfsB protein had its abundance increased in the presence of C12-HSL at all evaluated times, which is a suggestion that the cells may be susceptible to the action of nitrofurans or that AHLs present some toxicity. Overall, the presence of C12-HSL altered important pathways related to oxidative stress and stationary phase response in Salmonella.

Virtual screening of plant compounds and nonsteroidal anti-inflammatory drugs for inhibition of quorum sensing and biofilm formation in Salmonella

Salmonella belongs to the Enterobacteriaceae family which is widely distributed in the environment due to its adaptive capacity to stress conditions. In addition, Salmonella is able to perform a type of cell-to-cell communication called quorum sensing, which leads to differential gene expression. The quorum sensing system mediated by AI-1, acyl homoserine lactones (AHLs), is incomplete in Salmonella because the luxI homolog gene, which encodes for AI-1 synthase, is missing in the genome. However, a homologue of LuxR, known as SdiA, is present and allows the detection of signaling molecules produced by other species of bacteria, leading to regulation of gene expression, mainly related to virulence and biofilm formation. Thus, in view of the importance of quorum sensing on the physiology regulation of microorganisms, the aim of the present study was to perform a virtual screening of plant compounds and nonsteroidal anti-inflammatory drugs (NASIDs) for inhibition of quorum sensing by molecular docking and biofilm formation in Salmonella. In general, most plant compounds and all NSAIDs bound in, at least, one of the three modeled structures of SdiA proteins of Salmonella Enteritidis PT4 578. In addition, many tested compounds had higher binding affinities than the AHLs and the furanones which are inducers and inhibitors of quorum sensing, respectively. The Z-phytol and lonazolac molecules were good candidates for the in vitro inhibition tests of quorum sensing mediated by AI-1 and biofilm formation in Salmonella. Thus, this study directs future prospecting of plant extracts for inhibition of quorum sensing mechanism depending on AHL and biofilm formation. In addition, the use of inhibitors of quorum sensing and biofilm formation can be combined with antibiotics for better treatment efficacy, as well as the use of these compounds to design new drugs.