Exogenous Acyl-homoserine Lactones Research Articles

The effect of quorum sensing on cadmium- and lead-containing wastewater treatment using activated sludge: Removal efficiency, enzyme activity, and microbial community

Quorum sensing (QS) is prevalent in activated sludge processes; however, its essential role in the treatment of heavy metal wastewater has rarely been studied. Therefore, in this study, acyl homoserine lactone (AHL)-mediated QS was used to regulate the removal performance, enzyme activity, and microbial community of Cd- and Pb-containing wastewater in a sequencing batch reactor (SBR) over 30 cycles. The results showed that exogenous AHL strengthened the removal of Cd(II) and Pb(II) in their coexistence wastewater during the entire period. The removal of NH4+-N, total phosphorus, and chemical oxygen demand (COD) was also enhanced by the addition of AHL despite the coexistence of Cd(II) and Pb(II). Meanwhile, the protein content of extracellular polymeric substances was elevated and the microbial metabolism and antioxidative response were stimulated by the addition of AHL, which was beneficial for resistance to heavy metal stress and promoted pollutant removal by activated sludge. Microbial sequencing indicated that AHL optimized the microbial community structure, with the abundance of dominant taxa Proteobacteria and Unclassified_f_Enterobacteriaceae increasing by 73.9% and 59.2% maximally, respectively. This study offers valuable insights into the mechanisms underlying Cd(II) and Pb(II) removal as well as microbial community succession under AHL availability in industrial wastewater.

Comprehensive computational investigation for ligand recognition and binding dynamics of SdiA: a degenerate LuxR -type receptor in Klebsiella pneumoniae.

SdiA is a LuxR-type receptor that controls the virulence of Klebsiella pneumoniae, a Gram-negative bacterium that causes various infections in humans. SdiA senses exogenous acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2), two types of quorum sensing signals produced by other bacterial species. However, the molecular details of how SdiA recognizes and binds to different ligands and how this affects its function and regulation in K. pneumoniae still need to be better understood. This study uses computational methods to explore the protein-ligand binding dynamics of SdiA with 11 AHLs and 2 AI-2 ligands. The 3D structure of SdiA was predicted through homology modeling, followed by molecular docking with AHLs and AI-2 ligands. Binding affinities were quantified using MM-GBSA, and complex stability was assessed via Molecular Dynamics (MD) simulations. Results demonstrated that SdiA in Klebsiella pneumoniae exhibits a degenerate binding nature, capable of interacting with multiple AHLs and AI-2. Specific ligands, namely C10-HSL, C8-HSL, 3-oxo-C8-HSL, and 3-oxo-C10-HSL, were found to have high binding affinities and formed critical hydrogen bonds with key amino acid residues of SdiA. This finding aligns with the observed preference of SdiA for AHLs having 8 to 10 carbon-length acyl chains and lacking hydroxyl groups. In contrast, THMF and HMF demonstrated poor binding properties. Furthermore, AI-2 exhibited a low affinity, corroborating the inference that SdiA is not the primary receptor for AI-2 in K. pneumoniae. These findings provide insights into the protein-ligand binding dynamics of SdiA and its role in quorum sensing and virulence of K. pneumoniae.

Acyl homoserine lactone-based regulation strategy for improved methane production in anaerobic digestion of agricultural wastes

The acyl homoserine lactone (AHL)-based regulation strategy presents a considerable potential in improving anaerobic digestion (AD) efficiency of complex substrates. However, the reinforcement mechanisms are still unclear. In this study, the effects of different AHL types (C4-HSL, C7-HSL, C12-HSL) and different adding times (0 d, 5 d, 15 d) on AD performance of agricultural wastes (corn straw and cattle manure) were investigated. The results indicated that all types of AHLs exerted positive effects on AD, and the adding time rather than the AHL type was the key factor affecting AD processes. The C12-5d group obtained the highest accumulated methane production (310.7 ± 2.56 mL/g VS), which increased by 47.71% than that of the Control group. The exogenous AHLs facilitated the hydrolysis and acidification of complex substrates and the utilization of released low-molecular-weight organic acids in AD systems. Furthermore, the role of methanogenic archaea was upregulated and the dominance of bacteria was relatively weakened in AD systems, which favored the establishment of their balanced and symbiotic metabolic relationship. The enriched Methanobacterium strengthened the hydrogenotrophic methanogenesis pathway. This study provides new insights into the regulation strategy of AD for agricultural waste treatment based on AHL addition.

Cell-Cell Signaling Proteobacterial LuxR Solos: a Treasure Trove of Subgroups Having Different Origins, Ligands, and Ecological Roles.

Many proteobacteria possess LuxR solos which are quorum sensing LuxR-type regulators that are not paired with a cognate LuxI-type synthase. LuxR solos have been implicated in intraspecies, interspecies, and interkingdom communication by sensing endogenous and exogenous acyl-homoserine lactones (AHLs) as well as non-AHL signals. LuxR solos are likely to play a major role in microbiome formation, shaping, and maintenance through many different cell-cell signaling mechanisms. This review intends to assess the different types and discuss the possible functional roles of the widespread family of LuxR solo regulators. In addition, an analysis of LuxR solo types and variability among the totality of publicly available proteobacterial genomes is presented. This highlights the importance of these proteins and will encourage scientists to mobilize and study them in order to increase our knowledge of novel cell-cell mechanisms that drive bacterial interactions in the context of complex bacterial communities.

Potential roles of acyl homoserine lactones (AHLs) in nitrifying bacteria survival under certain adverse circumstances

Potential roles of quorum sensing (QS) in nitrifying bacteria activity and ecology, particularly under adverse circumstances have been rarely reported. Herein, eight lab-scale nitrification sequencing batch reactors, with or without adding acyl homoserine lactones (AHLs) were operated under adverse circumstances respectively. The results indicated that the introduction of AHLs significantly enhanced the nitrogen removal efficiency in the presence of nitrification inhibitors (dicyandiamide, DCD), accelerated the low temperature (10 °C) group into stable stage, and improved the utilization efficiency of AHLs in these two groups. Community analysis and qPCR further confirmed that AHLs significantly increased the abundance of nitrifying bacteria in low temperature group and DCD group, especially AOB. For normal condition (28 °C, pH = 8) or low pH level (5.5), however, the AHLs had no significant effect. Canonical correspondence analysis showed that nitrifying bacteria positively responded to AHLs, indicating that adding AHLs was an effective strategy to regulate nitrification process. However, under acid conditions, the effect of this regulatory mechanism was not significant, indicating that the influence of pH on the system was greater than that of AHLs. This study demonstrated that exogenous AHLs could enhance the competitiveness of nitrifying bacteria to utilize more resource and occupy space under some adverse environmental conditions.

Developing Cyanobacterial Quorum Sensing Toolkits: Toward Interspecies Coordination in Mixed Autotroph/Heterotroph Communities.

There has been substantial recent interest in the promise of sustainable, light-driven bioproduction using cyanobacteria, including developing efforts for microbial bioproduction using mixed autotroph/heterotroph communities, which could provide useful properties, such as division of metabolic labor. However, building stable mixed-species communities of sufficient productivity remains a challenge, partly due to the lack of strategies for synchronizing and coordinating biological activities across different species. To address this obstacle, we developed an inter-species communication system using quorum sensing (QS) modules derived from well-studied pathways in heterotrophic microbes. In the model cyanobacterium, Synechococcus elongatus PCC 7942 (S. elongatus), we designed, integrated, and characterized genetic circuits that detect acyl-homoserine lactones (AHLs), diffusible signals utilized in many QS pathways. We showed that these receiver modules sense exogenously supplied AHL molecules and activate gene expression in a dose-dependent manner. We characterized these AHL receiver circuits in parallel with Escherichia coli W (E. coli W) to dissect species-specific properties, finding broad agreement, albeit with increased basal expression in S. elongatus. Our engineered "sender" E. coli strains accumulated biologically synthesized AHLs within the supernatant and activated receiver strains similarly to exogenous AHL activation. Our results will bolster the design of sophisticated genetic circuits in cyanobacterial/heterotroph consortia and the engineering of QS-like behaviors across cyanobacterial populations.

A Novel and Efficient Platform for Discovering Noncanonical Quorum-Quenching Proteins.

Quorum sensing (QS) is a well-known chemical signaling system responsible for intercellular communication that is widespread in bacteria. Acyl-homoserine lactone (AHL) is the most-studied QS signal. Previously, bacterially encoded AHL-degrading enzymes were considered to be canonical quorum-quenching proteins that have been widely used to control pathogenic infections. Here, we report a novel platform that enabled the efficient discovery of noncanonical AHL quorum-quenching proteins. This platform initially asked bacteriologists to carry out comparative genomic analyses between phylogenetically related AHL-producing and non-AHL-producing members to identify genes that are conservatively shared by non-AHL-producing members but absent in AHL-producing species. These candidate genes were then introduced into recombinant AHL-producing E. coli to screen for target proteins with the ability to block AHL production. Via this platform, we found that non-AHL-producing Lysobacter containing numerous environmentally ubiquitous members encoded a conserved glycosyltransferase-like protein Le4759, which was experimentally shown to be a noncanonical AHL-quenching protein. Le4759 could not directly degrade exogenous AHL but rather recognized and altered the activities of multiple AHL synthases through protein-protein interactions. This versatile capability enabled Le4759 to block specific AHL synthase such as CarI from Pectobacterium carotovorum to reduce its protein abundance to suppress AHL synthesis, thereby impairing bacterial infection. Thus, this study provided bacteriologists with a unique platform to discover noncanonical quorum-quenching proteins that could be developed as promising next-generation drug candidates to overcome emerging bacterial antibiotic resistance. IMPORTANCE Targeting and blocking bacterial quorum sensing (QS), the process known as quorum quenching (QQ) is an effective mean to control bacterial infection and overcome the emerging antibiotic resistance. Previously, diverse QS signal-degradation enzymes are identified as canonical QQ proteins. Here, we provided a novel and universal platform that enabled to discover previously unidentified noncanonical QQ proteins that were unable to degrade acyl-homoserine lactone (AHL) but could block AHL generation by recognizing multiple AHL synthases via direct protein-protein interactions. Our findings are believed to trigger broad interest for bacteriologists to identify potentially widely distributed noncanonical QQ proteins that have great potential for developing next-generation anti-infectious drugs.

Regulation of exogenous acyl homoserine lactones on sludge settling performance: Monitoring via ultrasonic time-domain reflectometry.

Despite extensive studies, a comprehensive solution for sludge bulking has not yet been found. This study improves the sludge settling performance via quorum sensing (QS) by adding exogenous acyl homoserine lactones (AHLs). First, a novel approach based on ultrasonic time-domain reflectometry, which can automatically and in-situ assess a sludge volume index (SVI), was developed using the displacement in the ultrasonic spectra as a feasible indicator (R2=0.98, p<0.01). Next, the effects of typical AHLs, i.e., 3OC6-HSL, C12-HSL, and 3OC14-HSL, on sludge settling properties were investigated. Results indicated that the three AHLs significantly promoted the sludge settleability by 1.90, 2.03, and 1.62 times, respectively. The regulation mechanisms were investigated from the perspective of sludge physicochemical properties and biological community interactions. The draining degree of water to extracellular polymeric substances (EPS) significantly increased (p<0.05) with all three AHLs. Meanwhile, the hydrophobic tryptophan content increased with the addition of 3OC6-HSL and C12-HSL. Hence, EPS hydrophobicity was promoted, which is conducive to microbial aggregation. In addition, molecular ecological networks of activated sludge (AS) indicated that bacterial community structures were more complex and species interactions were more intense when adding 3OC6-HSL and C12-HSL. Meanwhile, additional keystones were identified, with the proportion of QS species increasing by 63.6% and 22.2%, respectively. Exogenous 3OC6-HSL eventually decreased the gross relative abundance of filamentous bacteria by 2.37%. Overall, appropriate AHLs could enhance community stability and microbial cooperation by strengthening the communication hub role of QS species, thereby suppressing the overgrowth of filamentous bacteria and improving the sludge settleability. This study provides an effective strategy to determine the appropriate AHL to rapidly eliminate filamentous bulking problems.

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 50nM and phytol at 2mM 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.

Effect of adding exogenous acyl homoserine lactone signal to Pseudomonas aeruginosa premature culture and prediction of signal binding domain in Rhamnolipids RhlA enzyme

Effect of adding exogenous acyl homoserine lactone signal to Pseudomonas aeruginosa premature culture and prediction of signal binding domain in Rhamnolipids RhlA enzyme

Quorum sensing-1 signaling of N-hexanoyl-L-homoserine lactone contributes to virulence in avian pathogenic Escherichia coli.

Avian pathogenic E. coli (APEC) caused avian colibacillosis is mostly common in poultry industry worldwide. APEC virulence factors lead to pathogenesis and the quorum sensing (QS) system is actively involved in the regulation of these virulence factors. Signaling molecules in QS are known as autoinducers (AIs). In QS-1, E. coli encodes a single LuxR homolog, i.e., SdiA, but does not express the LuxI homolog, an acyl-homoserine lactone (AHL) synthase of producing AI-1. Avian pathogenic E. coli (APEC) regulates its virulence genes expression in response to exogenous AHLs, but regulatory mechanisms of AHL and QS-1 are still unknown. This study targeted the APEC CE129 isolate as the reference strain, and the Yersinia enterocolitica yenI gene was expressed into APEC CE129. CE129/pyenI was conferred the ability to produce AHL signal. The CE129 SdiA mutant strain with an in-frame sdiA (AHL receptor) gene deletion was constructed by a λRed recombination system, which lost the ability to sense AHL. The goal of this study was to explore the function of QS-1 upon virulence and elucidate the regulatory effect of QS-1/AHL signals in the APEC strain. Adherence and invasion assays revealed that QS-1 affected APEC adherence and survival ability. APEC biofilm formation was also suppressed under C6HSL. Interestingly, APEC exhibited different phenotypes of acid tolerance and flagella expression when compared to enterotoxigenic E. coli or enterohemorrhagic E. coli (ETEC and EHEC, respectively). These findings enhance our understanding of the QS mechanism.

Effects of AHLs inhibitors and exogenous AHLs on the stability and activity of Anammox granules at low temperatures

This study investigated the relationship between acyl homoserine lactones (AHLs)-based quorum sensing (QS) and the properties of Anammox granular sludge at low temperatures (11-23°C). Results indicated that adding different concentrations of AHLs inhibitors reduced the content of N-hexanoyl-dl-homoserine lactone (C6-HSL) and N-octanoyl-dl-homoserinelactone (C8-HSL) in Anammox granules on different degrees at different operation temperatures, which led to the deterioration of granules stability and activity. The important role of endogenous C6-HSL and C8-HSL signals in maintaining Anammox granular sludge stability and activity in low-temperature conditions was revealed. In addition, in the process of reducing operation temperatures, another type of AHL signal (N-(3-oxooctanoyl)-l-homoserine lactone, 3OC8-HSL) was released by Anammox granules. The effects of exogenous C8-HSL on the strength, average diameter, and density of Anammox granules were closely related to the operation temperature. When the operation temperature ranged from 11°C to 16°C, the stability of granules could be significantly improved by exogenous C8-HSL. In addition, the addition of C6-HSL and 3OC8-HSL promoted the activity of Anammox granules when the operation temperatures of the reactors were 11-23°C. This study proposed a novel approach to improve the properties of Anammox granules at low temperatures from the perspective of QS. PRACTITIONER POINTS: Endogenous AHLs played an important role in maintaining the activity and stability of Anammox granules at 11-23°C. Exogenous C8-HSL improved the granules stability at the low temperature of 11-16°C. Exogenous C6-HSL or 3OC8-HSL promoted the granules activity at 11-23°C. Supply a novel way to improve the Anammox granules performance at low temperatures.

Improvement in calcified anaerobic granular sludge performance by exogenous acyl-homoserine lactones

Given the high content of Ca2+ in waste paper recycling wastewater, the anaerobic granular sludge (AnGS) undergoes calcification during wastewater treatment and affects the treatment efficiency. To restore the activity of calcified AnGS and improve the performance of AnGS, four types of N-acyl-homoserine lactones (AHLs) were added to the AnGS system while papermaking wastewater treatment. The addition of N-butyryl-DL-homoserine lactone(C4-HSL) and N-octanoyl-DL-homoserine lactone (C8-HSL) had an inhibitory affect the COD removal efficiency and SMA of sludge at the inception. The addition of N-hexanoyl-L-homoserine lactone (C6-HSL) has no obvious effect on the COD removal efficiency, but can improve the SMA of sludge more obviously. The addition of N-(β-ketocaproyl)-DL-homoserine lactone (3O-C6-HSL) can increased COD removal efficiency and promoted SMA together obviously. The addition of C6-HSL and 3O-C6-HSL can increase volatile suspended solid (VSS)/total suspended solid (TSS), and regulate extracellular polymeric substance (EPS) secretion in AnGS. Analysis of microbial sequencing revealed changes in the microbial community structure following AHL addition, which enhanced the methane metabolism pathway in sludge. The addition of C6-HSL, C8-HSL, and 3O-C6-HSL increased Methanosaeta population, thus increasing the aceticlastic pathway in sludge. Thus, exogenous AHLs can play an important role in regulating microbial community structure, and in improving the performance of AnGS.

RNA sequencing reveals the involvement of quorum sensing in dairy spoilage caused by psychrotrophic bacteria

Dairy spoilage caused by psychrotrophic bacteria has been reported to be regulated by acyl-homoserine-lactones (AHLs)-based quorum sensing (QS) system. However, the precise role of AHLs produced by psychrotrophic bacteria in dairy spoilage remains unclear. The aim of this study was to evaluate the effects of AHLs on dairy spoilage caused by Pseudomonas azotoformans and Serrita liquefaciens at the transcriptional level. The particle size and volatile compounds of milk were selected as spoilage indicators for investigating the involvement of AHLs in dairy spoilage. Furthermore, the in situ gene expressions of psychrotrophic bacteria in AHLs-treated milk during cold storage were explored by RNA sequencing for the first time. The results revealed that the milk particle size and content of acids in milk were increased by exogenous AHLs, which confirm the enhancing effect of AHLs on the quality deterioration of milk. Transcriptome analysis revealed that a number of core genes of strains were significantly differentially expressed when treated with exogenous AHLs, and QS coordinate the metabolic processes within tested strains. Most of genes involving in the bacterial growth and metabolism, enzymes production, and stress response were up-regulated by exogenous AHLs. The results elucidate the potential involvement of AHLs in dairy spoilage caused by psychrotrophic bacteria. This would give clue for novel strategy of controlling microbial spoilage in dairy products.

Long-term exogenous addition of synthetic acyl homoserine lactone enhanced the anaerobic granulation process

Although adding long-term acyl homoserine lactone (AHL) over one month was highly instructive for the development of an AHL-based anaerobic granulation strategy, the role of long-term exogenous AHL at different concentrations in the granulation process was poorly understood due to commercial exogenous AHL's extremely high cost. In this study, organic synthesis of N-decanoyl-homoserine lactone (C10-HSL) was employed for the first time to drastically reduce the cost of the AHL addition. Daily dosages of exogenous C10-HSL at 50 nM, 500 nM and 5000 nM were separately added into anaerobic bioreactors to promote the granulation process for as long as 168 days. 50 nM C10-HSL showed a negligible effect on the granulation process while 5000 nM C10-HSL achieved the best performance with the highest chemical oxygen demand (COD) removal, largest granule size and best extracellular polymeric substance production. Bacterial analysis indicated that exogenous C10-HSL showed a concentration-related effect in bacterial community organization. Besides, addition of 5000 nM C10-HSL resulted in the greatest promotion of Methanosaeta which was extremely important to the formation of anaerobic granule. This study provides a foundation for the future application of long-term exogenous AHL manipulation to improve the granulation process in an engineered ecosystem.

AHLs-produced bacteria in refrigerated shrimp enhanced the growth and spoilage ability of Shewanella baltica.

Shewanella baltica is the predominant bacteria in spoiled shrimp (Litopenaeus vannamei), however, the spoilage ability and the mechanism of S. baltica is still unknown. S. baltica can't produce the signal molecule of acyl-homoserine-lactones (AHLs), so the aim of this study was to investigate how wild type S. baltica SA03 (WT SA03) eavesdrop exogenous AHLs to enhance its spoilage ability through LuxR receptor. The results indicated that Aeromonas spp. (Aer), Acinetobacter spp. (Aci) and Serratia spp. (Ser) isolated from refrigerated shrimp can produce different AHLs. WT SA03 can eavesdrop the AHLs of Aer (C4-HSL), Aci (O-C6-HSL) and Ser (C6-HSL, O-C6-HSL) to enhance its growth, especially Ser. Exogenous C4-HSL and C6-HSL enhanced biofilm formation of WT SA03, and C6-HSL and O-C6-HSL enhanced thioredoxin reductase trxB mRNA expression. However, the luxR mutant of WT SA03 (ΔluxR SA03) lost or weakened the role of using environmental AHLs. In vivo experiments, the lag time of WT SA03 was shortened by 6.4h, 6.2h and 14.4h by co-inoculated with Aer, Aci and Ser, respectively. The total volatile basic nitrogen (TVB-N) were significantly enhanced in the samples co-inoculated with WT SA03 and Aer (or Aci, Ser) than those of ΔluxR SA03 and Aer (or Aci, Ser) (p < 0.05). The results showed that S. baltica SA03 can utilize AHLs produced by other bacteria to enhance its growth and spoilage ability through LuxR receptor system. Quorum sensing based on AHLs of bacteria might as the potential targets for food spoilage control.

Exogenous acyl-homoserine lactones adjust community structures of bacteria and methanogens to ameliorate the performance of anaerobic granular sludge

Quorum sensing (QS) signalling has been extensively studied in single species populations, activated sludge, biofilm and aerobic granular sludge. However, ecological roles of QS in anaerobic granular sludge, particularly in the content of the relationship between QS signalling and microbial community composition and function, have been rarely reported. Herein, five acyl-homoserine lactones (AHLs) molecules were added in the anaerobic granular sludge system for treating traditional Chinese medicine (TCM) wastewater respectively. The results indicated that the introduction of specific AHLs could enhance the abilities of organic matters removal and methanation in anaerobic granular sludge, and meanwhile, exogenous AHLs played an important role to regulate the concentration of EPS. Sequencing analysis indicated that microbial community structures of bacteria and methanogens changed to varying degrees by adding AHLs. This study suggested that exogenous AHLs could play a role in mediating microbial community structure, thereby enhancing the performance of anaerobic granular sludge. The regulatory mechanism of AHLs on community structure was discussed, and a speculative action model was established. Exogenous regulation by selective enhancement of AHLs-mediated QS in anaerobic granular sludge provided an innovative and attractive strategy for strengthening wastewater treatments.

Metabolomics Uncovers the Regulatory Pathway of Acyl-homoserine Lactones Based Quorum Sensing in Anammox Consortia.

Acyl-homoserine lactones (AHLs)-mediated quorum sensing in bacterial communities have been extensively observed. However, the metabolic pathways regulated by AHLs in bacteria remain elusive. Here, we combined long-term reactor operation with microbiological and metabolomics analyses to explore the regulatory pathways for different AHLs in anammox consortia, which perform promising nitrogen removal for wastewater treatment. The results showed that no obvious shifts induced by exogenous AHLs occurred in the microbial community and, mainly, dosing AHLs induced changes in the metabolites. 3OC6-HSL, C6-HSL, and C8-HSL controlled the electron transport carriers that influence the bacterial activity. In contrast, only 3OC6-HSL regulated LysoPC(20:0) metabolism, which affected bacterial growth. AHLs mainly regulated the synthesis of the amino acids Ala, Val, and Glu and selectively regulated Asp and Leu to affect extracellular proteins. Simultaneously, all the AHLs regulated the ManNAc biosynthetic pathways, while OC6-HSL, OC8-HSL, and C6-HSL particularly enriched the UDP-GlcNAc pathway to promote exopolysaccharides, resulting in different aggregation levels of the anammox consortia. Our results not only provide the first metabolic insights into the means by which AHLs affect anammox consortia but also hint at potential strategies for overcoming the limitations of the long start-up period required for wastewater treatment by anammox processing.

Pseudomonas syringae pv. syringae B728a Regulates Multiple Stages of Plant Colonization via the Bacteriophytochrome BphP1.

ABSTRACTLight may be an important environmental signal for plant-associated bacteria, particularly those that live on leaves. An integrated network of red/far-red- and blue-light-responsive photosensory proteins is known to inhibit swarming motility in the foliar plant pathogen Pseudomonas syringae pv. syringae B728a. Here we elucidated factors in the red/far-red-light-sensing bacteriophytochrome BphP1 signal transduction pathway and report evidence for a role of BphP1 in multiple stages of the P. syringae B728a life cycle. We report that BphP1 signaling involves the downstream regulator Bsi (bacteriophytochrome-regulated swarming inhibitor) and an acyl-homoserine lactone (AHL) signal. Loss of bphP1 or bsi resulted in the early initiation of swarm tendrils during swarming motility, a phenotype that was dependent on red/far-red light and reversed by exogenous AHL, illustrating that the BphP1-Bsi-AHL pathway inhibits the transition from a sessile state to a motile state. Loss of bphP1 or bsi resulted in larger water-soaked lesions induced on bean (Phaseolus vulgaris) pods and enhanced movement from soil and buried plant tissues to seeds, demonstrating that BphP1 and Bsi negatively regulate virulence and bacterial movement through soil to seeds. Moreover, BphP1, but not Bsi, contributed to leaf colonization; loss of bphP1 reduced survival on leaves immediately following inoculation but enhanced the size of the subsequently established populations. Neither Bsi nor Smp, a swarm motility-promoting regulator identified here, affected leaf colonization, indicating that BphP1-mediated contributions to leaf colonization are, at least in part, independent of swarming motility. These results demonstrate that P. syringae B728a red-light sensing involves a multicomponent, branched regulatory pathway that affects several stages of its life cycle.

Quorum sensing signals enhance the electrochemical activity and energy recovery of mixed-culture electroactive biofilms

The impacts of exogenous or endogenous quorum sensing (QS) signaling molecules on mixed-culture electroactive biofilms (EABs), especially extracellular polymeric substances (EPS) and exoelectrogens using direct electron transfer mechanism inside EABs are poorly understood. This research focuses on the influence of acylhomoserine lactones (AHLs), the most common QS signaling molecules for gram negative bacteria, on mixed-culture EABs. Results indicated that both exogenous and endogenous AHLs played the role as regulators to improve the electrochemical activities of EABs. The energy recovery of MFCs increased from 20.5% ± 3.9% to 28.3% ± 4.1% with endogenous AHLs and further rose to 36.2% ± 5.1% with exogenous AHLs, and the start-up period of MFCs shortened from 13 days to 10 days with endogenous AHLs and further reduced to 4 days in the presence of exogenous AHLs. The influences of exogenous and endogenous AHLs were non-instantaneous. They improved some intrinsic properties, i.e. the electrode-associated biomass, the biofilm compactness and the ratio of live/dead cells to obtain superior EABs. Meanwhile, both endogenous and exogenous AHLs increased the concentration and redox activities of EPS. Besides, endogenous AHLs enhanced the diversity of EPS components. Noteworthily, the relative abundance of Geoboacter sp. which is the typical microbe using direct electron transfer mechanism is raised by exogenous AHLs, though so far neither known chemical QS-related gene nor protein has been reported in this genus. These findings will increase the current understanding of QS in EABs and open up an opportunity for regulating mixed-culture MFCs via QS.