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

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.

The quorum sensing molecule C12-HSL promotes biofilm formation and increases adrA expression in Salmonella Enteritidis under anaerobic conditions

Acyl-homoserine lactones (AHLs) are quorum-sensing signaling molecules in Gram-negative bacteria and positively regulate biofilm formation in Salmonella under specific conditions. In this study, biofilm formation in Salmonella enterica was evaluated at 28 and 37 °C, under aerobic and anaerobic conditions. Additionally, the influence of the N-dodecanoyl-DL-homoserine lactone (C12-HSL) on biofilm formation and the expression of genes related to the synthesis of structural components, regulation, and quorum sensing was assessed under anaerobiosis at 28 and 37 °C. Biofilm formation was found not to be influenced by the atmospheric conditions at 28 °C. However, it was reduced at 37 °C under anaerobiosis. C12-HSL enhanced biofilm formation at 37 °C under anaerobiosis and increased the expression of the adrA and luxS genes, suggesting an increase in c-di-GMP, a second messenger that controls essential physiological functions in bacteria. These results provide new insights into the regulation of biofilm formation in Salmonella under anaerobic conditions.

Joining the bacterial conversation: increasing the cultivation efficiency of soil bacteria with acyl-homoserine lactones and cAMP

IMPORTANCE

Microorganisms are a repository of interesting metabolites and functions. Therefore, accessing them is an important exercise for advancing not only basic questions about their physiology but also to advance technological applications. In this sense, increasing the culturability of environmental microorganisms remains an important endeavor for modern microbiology. Because microorganisms do not live in isolation in their environments, molecules can be added to the cultivation strategies to "inform them" that they are present in growth-permissive environmental conditions. Signaling molecules such as acyl-homoserine lactones and 3',5'-cyclic adenosine monophosphate belong to the plethora of molecules used by bacteria to communicate with each other in a phenomenon called quorum sensing. Therefore, including quorum sensing molecules can be an incentive for microorganisms, specifically soil bacteria, to increase their numbers on solid media.

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.

Genomic and transcriptomic characterization of the Collimonas quorum sensing genes and regulon

Collimonads are well-adapted to nutrient-poor environments. They are known to hydrolyse chitin, produce antifungal metabolites, weather minerals, and are effective biocontrol agents protecting plants from fungal diseases. The production of N-acyl homoserine lactones (AHLs) was suggested to be a conserved trait of collimonads, but little is known about the genes that underlie this production or the genes that are controlled by AHLs. To improve our understanding of the role of AHLs in the ecology of collimonads, we carried out transcriptomic analyses, combined with chemical and functional assays, on strain Collimonas pratensis PMB3(1). The main AHLs produced by this strain were identified as 3-hydroxy-hexa- and octa-noyl-homoserine lactone. Genome analysis permitted to identify putative genes coding for the autoinducer synthase (colI) and cognate transcriptional regulator (colR). The ability to produce AHLs was lost in ΔcolI and ΔcolR mutants. Functional assays revealed that the two mutants metabolized glucose, formate, oxalate, and leucine better than the wild-type (WT) strain. Transcriptome sequencing analyses revealed an up-regulation of different metabolic pathways and of motility in the QS-mutants compared to the WT strain. Overall, our results provide insights into the role of the AHL-dependent regulation system of Collimonas in environment colonization, metabolism readjustment, and microbial interactions.

SdiA Enhanced the Drug Resistance of Cronobacter sakazakii and Suppressed Its Motility, Adhesion and Biofilm Formation

Cronobacter sakazakii is a common foodborne pathogen, and the mortality rate of its infection is as high as 40–80%. SdiA acts as a quorum sensing regulator in many foodborne pathogens, but its role in C. sakazakii remains unclear. Here, we further determined the effect of the sdiA gene in C. sakazakii pathogenicity. The SdiA gene in C. sakazakii was knocked out by gene editing technology, and the biological characteristics of the ΔsdiA mutant of C. sakazakii were studied, followed by transcriptome analysis to elucidate its effects. The results suggested that SdiA gene enhanced the drug resistance of C. sakazakii but diminished its motility, adhesion and biofilm formation ability and had no effect on its growth. Transcriptome analysis showed that the ΔsdiA upregulated the expression levels of D-galactose operon genes (including dgoR, dgoK, dgoA, dgoD and dgoT) and flagella-related genes (FliA and FliC) in C. sakazakii and downregulated the expression levels of related genes in the type VI secretion system (VasK gene was downregulated by 1.53-fold) and ABC transport system (downregulated by 1.5-fold), indicating that SdiA gene was related to the physiological metabolism of C. sakazakii. The results were useful for clarifying the pathogenic mechanism of C. sakazakii and provide a theoretical basis for controlling bacterial infection.

Autoinducer-2-mediated quorum-sensing system resists T4 phage infection in Escherichia coli

In response to the restriction of nutrients and predation by natural enemies, bacteria have evolved complex coping strategies to ensure the reproduction and survival of individual species. Quorum sensing (QS) is involved in the bacterial response to phage predation and regulation of cellular metabolism. However, to date, no clear evidence exists regarding the involvement of autoinducer-2 (AI-2)-mediated QS systems in Escherichia coli in response to the challenges of nutrient restriction and phage infection. In this study, the role of the AI-2-mediated QS system in resisting T4 phage infection and regulating cell mechanisms in E. coli was revealed for the first time. This effect of the AI-2-mediated QS was achieved by simultaneously downregulating the T4 absorption site and carbon and glucose metabolism. Additionally, we found that lsrB, a metabolic brake, participates in AI-2-mediated regulation and maintenance of the normal metabolic balance of cells. The novel phage defense strategy and regulation and maintenance of cellular metabolism effectively limited the expansion of the phage population.

Salmonella spp. quorum sensing: an overview from environmental persistence to host cell invasion

Salmonella spp. is one of the main foodborne pathogens around the world. It has a cyclic lifestyle that combines host colonization with survival outside the host, implying that Salmonella has to adapt to different conditions rapidly in order to survive. One of these environments outside the host is the food production chain. In this environment, this foodborne pathogen has to adapt to different stress conditions such as acidic environments, nutrient limitation, desiccation, or biocides. One of the mechanisms used by Salmonella to survive under such conditions is biofilm formation. Quorum sensing plays an important role in the production of biofilms composed of cells from the same microorganism or from different species. It is also important in terms of food spoilage and regulates the pathogenicity and invasiveness of Salmonella by regulating Salmonella pathogenicity islands and flagella. Therefore, in this review, we will discuss the genetic mechanism involved in Salmonella quorum sensing, paying special attention to small RNAs and their post-regulatory activity in quorum sensing. We will further discuss the importance of this cell-to-cell communication mechanism in the persistence and spoilage of Salmonella in the food chain environment and the importance in the communication with microorganisms from different species. Subsequently, we will focus on the role of quorum sensing to regulate the virulence and invasion of host cells by Salmonella and on the interaction between Salmonella and other microbial species. This review offers an overview of the importance of quorum sensing in the Salmonella lifestyle.

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.