RESUMEN

The inhibitory effects of zinc oxide nanoparticles (ZnO NPs) and impacts of N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) on biological nitrogen removal (BNR) performance have been well-investigated. However, the effects of ammonia nitrogen (NH4+-N) concentrations on NP toxicity and AHL regulation have seldom been addressed yet. This study consulted on the impacts of ZnO NPs on BNR systems when high NH4+-N concentration was available. The synergistic toxic effects of high-strength NH4+-N (200 mg/L) and ZnO NPs resulted in decreased ammonia oxidation rates and dropped the nitrogen removal efficiencies by 17.5% ± 0.2%. The increased extracellular polymeric substances (EPS) production was observed in response to the high NH4+-N and ZnO NP stress, which indicated the defense mechanism against the toxic effects in the BNR systems was stimulated. Furthermore, the regulatory effects of exogenous N-decanoyl-homoserine lactone (C10-HSL)-mediated QS system on NP-stressed BNR systems were revealed to improve the BNR performance under different NH4+-N concentrations. The C10-HSL regulated the intracellular reactive oxygen species levels, denitrification functional enzyme activities, and antioxidant enzyme activities, respectively. This probably synergistically enhanced the defense mechanism against NP toxicity. However, compared to the low NH4+-N concentration of 60 mg/L, the efficacy of C10-HSL was inhibited at high NH4+-N levels of 200 mg/L. The findings provided the significant application potential of QS system for BNR when facing toxic compound shock threats.

Asunto(s)

RESUMEN

Microcystis-dominated cyanobacterial blooms (MCBs) frequently occur in freshwaters worldwide due to massive Microcystis colony formation and severely threaten human and ecosystem health. Quorum sensing (QS) is a direct cause of Microcystis colony formation that drives MCBs outbreak by regulating Microcystis population characteristics and behaviors. Many novel findings regarding the fundamental knowledge of the Microcystis QS phenomenon and the signaling molecules have been documented. However, little effort has been devoted to comprehensively summarizing and discussing the research progress and exploration directions of QS signaling molecules-mediated QS system in Microcystis. This review summarizes the action process of N-acyl homoserine lactones (AHLs) as major signaling molecules in Microcystis and discusses the detailed roles of AHL-mediated QS system in cellular morphology, physiological adaptability, and cell aggregation for colony formation to strengthen ecological adaptability and competitive advantage of Microcystis. The research progress on QS mechanisms in Microcystis are also summarized. Compared to other QS systems, the LuxI/LuxR-type QS system is more likely to be found in Microcystis. Also, we introduce quorum quenching (QQ), a QS-blocking process in Microcystis, to emphasize its potential as QS inhibitors in MCBs control. Finally, in response to the research deficiencies and gaps in Microcystis QS, we propose several future research directions in this field. This review deepens the understanding on Microcystis QS knowledge and provide theoretical guidance in developing strategies to monitor, control, and harness MCBs.

RESUMEN

Dasania marina (isolate SD1D, with 98.5% sequence similarity to Dasania marina DMS 21967 KOPRI 20902) is a marine bacterium that was isolated from ballast tank fluids as part of a biofilm study in 2014. Our previous work indicated that although this strain produced no detectable biofilm, it was the only isolate to produce N-acyl homoserine lactones (AHLs) in assays using the broad-range reporter strain, Agrobacterium tumefaciens KYC55. The goal of the current study was to determine the types of AHL molecules produced by the D. marina isolate using gas chromatography-mass spectroscopy (GCMS) and C4- to C14-AHL as standards. A time course assay indicated that the D. marina strain produced the highest level of AHLs at 20 h of growth. When extracts were subjected to GCMS, detectable levels of C8- and C10-AHL and higher levels of C12-AHL were observed. Interestingly, several biofilm-forming isolates obtained from the same source also produced detectable amounts of several AHLs. Of the isolates tested, a strain designated SD5, with 99.83% sequence similarity to Alteromonas tagae BCRC 17571, produced unstable biofilms, yet detectable levels of C6-, C8-, C10- and C12-AHL, and isolate SD8, an Alteromonas oceani S35 strain (98.85% sequence similarity), produced robust and stable biofilms accompanied by detectable levels of C8- and C12-AHL. All isolates tested produced C12-AHL at higher levels than the other AHLs. Results from this study suggest that quorum sensing and biofilm formation are uncoupled in D. marina. Whether the suite of AHLs produced by this isolate could modulate biofilm formation in other strains requires further study.

RESUMEN

The effects of three typical N-acyl-homoserine lactones (AHLs) on the tolerance of biological nitrogen removal (BNR) system to chronic exposure of zinc oxide nanoparticles (NPs) were investigated. C4-HSL successfully delayed the crash time of nitrogen removal performances in the NP-stressed system, while C6-HSL and C10-HSL maintained total nitrogen removal efficiencies throughout the 90-day NP exposure. All three AHLs increased NPs' contents captured in extracellular polymeric substances, alleviating membrane damage and preserving floc structure. The activities of tricarboxylic acid cycle-related enzymes and the relative abundances of BNR-related functional genes and genera were significantly enhanced. Besides, C6-HSL and C10-HSL augmented antioxidant enzyme activities and the abundances of functional genes and metabolites related to antioxidation, flagellar assembly, and chemotaxis, which synergistically reduced the reactive oxygen species' excessive accumulation. The tested AHLs effectively enhanced BNR systems' tolerance to chronic NP exposure, providing inspiration for quorum sensing applications in emerging contaminant removal.

Asunto(s)

RESUMEN

A dynamic mucous layer containing numerous micro-organisms covers the surface of corals and has multiple functions including both removal of sediment and "food gathering."1 It is likely to also act as the primary barrier to infection; various proteins and compounds with antimicrobial activity have been identified in coral mucus, though these are thought to be largely or exclusively of microbial origin. As in Hydra,2 anti-microbial peptides (AMPs) are likely to play major roles in regulating the microbiomes of corals.3,4 Some eukaryotes employ a complementary but less obvious approach to manipulate their associated microbiome by interfering with quorum signaling, effectively preventing bacteria from coordinating gene expression across a population. Our investigation of immunity in the reef-building coral Acropora millepora,5 however, led to the discovery of a coral gene referred to here as AmNtNH1 that can inactivate a range of acyl homoserine lactones (AHLs), common bacterial quorum signaling molecules, and is induced on immune challenge of adult corals and expressed during the larval settlement process. Closely related proteins are widely distributed within the Scleractinia (hard corals) and some other cnidarians, with multiple paralogs in Acropora, but their closest relatives are bacterial, implying that these are products of one or more lateral gene transfer events post-dating the cnidarian-bilaterian divergence. The deployment by corals of genes used by bacteria to compete with other bacteria reflects a mechanism of microbiome manipulation previously unknown in Metazoa but that may apply more generally.

Asunto(s)

RESUMEN

Quorum quenching refers to any mechanism that inhibits quorum sensing processes. In this study, quorum quenching activity among bacteria inhabiting riverside soil was screened, and a novel Gram-stain-negative, rod shaped bacterial strain designated MMS21-HV4-11T, which showed the highest level of quorum quenching activity, was isolated and subjected to further analysis. Strain MMS21-HV4-11T could be assigned to the genus Reyranella of Alphaproteobacteria based on the 16S rRNA gene sequence, as the strain shared 98.74% sequence similarity with Reyranella aquatilis seoho-37T, and then 97.87% and 97.80% sequence similarity with Reyranella soli KIS14-15T and Reyranella massiliensis 521T, respectively. The decomposed N-acyl homoserine lactone was restored at high concentrations under acidic conditions, implying that lactonase and other enzyme(s) are responsible for quorum quenching. The genome analysis indicated that strain MMS21-HV4-11T had two candidate genes for lactonase and one for acylase, and expected protein structures were confirmed. In the quorum sensing inhibition assay using a plant pathogen Pectobacterium carotovorum KACC 14888, development of soft rot was significantly inhibited by strain MMS21-HV4-11T. Besides, the swarming motility by Pseudomonas aeruginosa PA14 was significantly inhibited in the presence of strain MMS21-HV4-11T. Since the isolate did not display direct antibacterial activity against either of these species, the inhibition was certainly due to quorum quenching activity. In an extended study with the type strains of all known species of Reyranella, all strains were capable of degrading N-acyl homoserine lactones (AHLs), thus showing quorum quenching potential at the genus level. This is the first study on the quorum quenching potential and enzymes responsible in Reyranella. In addition, MMS21-HV4-11T could be recognized as a new species through taxonomic characterization, for which the name Reyranella humidisoli sp. nov. is proposed (type strain = MMS21-HV4-11 T = KCTC 82780 T = LMG 32365T).

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

Stringent response and quorum sensing (QS) are two essential mechanisms that control bacterial global metabolism for better survival. Sphingomonads are a clade of bacteria that survive successfully in diverse ecosystems. In silico survey indicated that 36 out of 79 investigated sphingomonads strains contained more than one luxI homolog, the gene responsible for the biosynthesis of QS signal acyl homoserine lactones (AHLs). Investigation of the regulatory effects of the stringent response gene rsh on QS related bioactivities were carried out using rsh mutants of Sphingobium japonicum UT26 and Sphingobium sp. SYK-6, both had three luxI homologs. Results indicated that deletion of rsh upregulated the overall production of AHLs and extracellular polymeric substances (EPS) in both UT26 and SYK-6 in rich medium, but affected expressions of these luxI/luxR homologs in different ways. In the poor medium (1% LB), rsh mutant of SYK-6 significantly lost AHLs production in broth cultivation but not in biofilm cultivation. The regulatory effects of rsh on QS activities were growth phase dependent in UT26 and culture condition dependent in SYK-6. Our results demonstrated the negative regulatory effect of rsh on QS activities in sphingomonads, which were very different from the positive effect found in sphingomonads containing only one luxI/R circuit. This study extends the current knowledge on the intricate networks between stringent response and QS system in sphingomonads, which would help to understand their survival advantage.

RESUMEN

Cyclic adenosine monophosphate (cAMP) is an important second messenger in cells, mediating various stimulation signals such as the growth and development of organisms and stress and participating in regulating various biological processes of cells. This article explores the quantitative determination of cAMP in plants using High-Performance Liquid Chromatography (HPLC) and applies this method to analyzing the changes in cAMP content during the process of plant response to the bacterial quorum sensing signal N-acyl homoserine lactone (AHL). Research has shown that the optimal detection conditions for HPLC are as follows: the chromatographic column is Venusil MP C18 (2), the mobile phase is methanol-water (0.1% trifluoroacetic acid) (v:v, 10:90), the detection wavelength is 259 nm, the column temperature is 35 °C, and the flow rate is 0.8 mL/min. The precision of the standard sample of this method is 98.21%, the precision of the sample is 98.87%, and the recovery rate is 101.067%. The optimal extraction conditions for cAMP in Arabidopsis are to use 15% methanol ultrasonic extraction for 10 min, followed by a 40 °C water bath for 4 h. Bacterial AHL signal processing can significantly stimulate an increase in cAMP levels in Arabidopsis leaves and roots. The establishment of HPLC detection methods for the cAMP content in plants is of great significance for in-depth research on the signal transduction mechanisms of plant-bacterial interactions.

Asunto(s)

RESUMEN

Acyl-homoserine lactone (AHL) serves as a key signaling molecule for quorum sensing (QS) in bacteria. QS-related genes and physiological processes in Microcystis aeruginosa remain elusive. In this study, we elucidated the regulatory role of AHL-mediated QS in M. aeruginosa. Using AHL activity extract and transcriptomic analysis, we revealed significant effects of the AHL on growth and photosynthesis. AHL significantly increased chlorophyll a (Chl-a) content and accelerated photosynthetic rate thereby promoting growth. Transcriptome analysis revealed that AHL stimulated the up-regulation of photosynthesis-related genes (apcABF, petE, psaBFK, psbUV, etc.) as well as nitrogen metabolism and ribosomal metabolism. In addition, AHL-regulated pathways are associated with lipopolysaccharide and phenazine synthesis. Our findings deepen the understanding of the QS system in M. aeruginosa and are important for gaining insights into the role of QS in Microcystis bloom formation. It also provides new insights into the prevalence of M. aeruginosa in water blooms.

Asunto(s)

RESUMEN

Developing a biofilm biomarker detector and inhibitor will immensely benefit efforts geared at curbing infectious diseases and microbiologically induced corrosion of medical implants, marine vessels and buried steel pipelines. N-Acyl homoserine lactones (AHLs) are important biomarkers gram-negative bacteria use for communication. In this work, we investigated the interactions between three AHL molecules and graphene oxide (GO) and ZnO nanomaterials embedded in conjugated poly(3,4-ethylenedioxythiophene) (PEDOT) film. The results show that PEDOT/GO/ZnO detected AHLs to a considerable extent with adsorption enthalpies of -4.02, -4.87 and -4.97 KJ/mol, respectively, for N-(2-oxotetrahydrofuran-3-yl)heptanamide (AHL1), 2-hydroxy-N-(2-oxotetrahydrofuran-3-yl)nonanamide (AHL2) and (E)-3-(3-hydroxyphenyl)-N-(2-oxotetrahydrofuran-3-yl)acrylamide (AHL3) molecules. The ZnO nanoparticles facilitated charge redistribution and transfer, thereby enhancing the conductivity and overall sensitivity of the substrate toward the AHLs. The adsorption distance and sites of interactions further tuned the charge migration and signal generation by the substrate, thus affirming the suitability of the modeled thin film as a sensor material. Excellent stability and conductivity were maintained before and after the adsorption of each AHL molecule. Moreover, the desorption time for each AHL molecule was calculated, and the result affirmed that the modeled film materials are promising for developing highly sensitive biosensors.Communicated by Ramaswamy H. Sarma.

RESUMEN

Many Gram-negative bacteria use N-acyl-L-homoserine lactone (AHL) signals to coordinate phenotypes such as biofilm formation and virulence factor production. Quorum-quenching enzymes, such as AHL acylases, chemically degrade these molecules which prevents signal reception by bacteria and inhibits undesirable biofilm-related traits. These capabilities make acylases appealing candidates for controlling microbes, yet candidates with high activity levels and substrate specificity and that are capable of being formulated into materials are needed. In this work, we undertook engineering efforts against two AHL acylases, PvdQ and MacQ, to generate these improved properties using the Protein One-Stop Shop Server. The engineering of acylases is complicated by low-throughput enzymatic assays. Alleviating this challenge, we report a time-course kinetic assay for AHL acylases that monitors the real-time production of homoserine lactone. Using the assay, we identified variants of PvdQ that were significantly stabilized, with melting point increases of up to 13.2°C, which translated into high resistance against organic solvents and increased compatibility with material coatings. While the MacQ mutants were unexpectedly destabilized, they had considerably improved kinetic properties, with >10-fold increases against N-butyryl-L-homoserine lactone and N-hexanoyl-L-homoserine lactone. Accordingly, these changes resulted in increased quenching abilities using a biosensor model and greater inhibition of virulence factor production of Pseudomonas aeruginosa PA14. While the crystal structure of one of the MacQ variants, M1, did not reveal obvious structural determinants explaining the observed changes in kinetics, it allowed for the capture of an acyl-enzyme intermediate that confirms a previously hypothesized catalytic mechanism of AHL acylases.

Asunto(s)

RESUMEN

Quorum sensing (QS) is a widespread regulatory mechanism in Gram-negative bacteria, primarily involving the secretion of N-acyl homoserine lactone (AHL) to facilitate population density sensing. However, the existence of QS in blue-green algae, a subset of photoautotrophic Gram-negative bacteria forming high-density communities in water blooms, remains elusive. This study delves into the unexplored realm of QS in Microcystis aeruginosa (M. aeruginosa) by investigating AHL-related regulatory mechanisms and their impact on various physiological processes. Utilizing high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) and biosensors, a hitherto unknown long-chain AHL exhibiting a mass-to-charge ratio of 318 was identified in sterile M. aeruginosa cultures. Our investigation focused on discerning correlations between AHL activity fluctuations and key parameters such as microcystin (MC-LR) production, algal density, photosynthesis, buoyancy, and aggregation. Furthermore, the AHL extract was introduced during the logarithmic stage of M. aeruginosa cultures to observe the response in physiological processes. The results revealed that AHL, functioning as an autoinducer (AI), positively influenced algal growth and photosynthesis, as evidenced by the upregulated photosynthetic conversion efficiency of PSI and chlorophyll synthesis gene (psbA). AI also played a crucial role in altering surface characteristics through the synthesis of polysaccharides and proteins in EPS, subsequently promoting cell aggregation. Concomitantly, AI upregulated mcyD, enhancing the synthesis of MC-LR. Notably, our investigation pinpointed the initiation of QS in Microcystis at a density of approximately 1.22 × 10^7 cells/mL. This groundbreaking evidence underscores the regulatory role of AI in governing the physiological processes of growth, aggregation, buoyancy, and MC-LR production by activating pertinent gene expressions. This study significantly expands the understanding of QS in AHL, providing crucial insights into the regulatory networks operating in blue-green algae.

Asunto(s)

RESUMEN

The last step of the initiation phase of fatty acid biosynthesis in most bacteria is catalyzed by the 3-ketoacyl-acyl carrier protein (ACP) synthase III (FabH). Pseudomonas syringae pv. syringae strain B728a encodes two FabH homologs, Psyr_3467 and Psyr_3830, which we designated PssFabH1 and PssFabH2, respectively. Here, we explored the roles of these two 3-ketoacyl-ACP synthase (KAS) III proteins. We found that PssFabH1 is similar to the Escherichia coli FabH in using acetyl-acetyl-coenzyme A (CoA ) as a substrate in vitro, whereas PssFabH2 uses acyl-CoAs (C4-C10) or acyl-ACPs (C6-C10). Mutant analysis showed that neither KAS III protein is essential for the de novo fatty acid synthesis and cell growth. Loss of PssFabH1 reduced the production of an acyl homoserine lactone (AHL) quorum-sensing signal, and this production was partially restored by overexpressing FabH homologs from other bacteria. AHL production was also restored by inhibiting fatty acid elongation and providing exogenous butyric acid. Deletion of PssFabH1 supports the redirection of acyl-ACP toward biosurfactant synthesis, which in turn enhances swarming motility. Our study revealed that PssFabH1 is an atypical KAS III protein that represents a new KAS III clade that functions in providing a critical fatty acid precursor, butyryl-ACP, for AHL synthesis.IMPORTANCEAcyl homoserine lactones (AHLs) are important quorum-sensing compounds in Gram-negative bacteria. Although their formation requires acylated acyl carrier proteins (ACPs), how the acylated intermediate is shunted from cellular fatty acid synthesis to AHL synthesis is not known. Here, we provide in vivo evidence that Pseudomonas syringae strain B728a uses the enzyme PssFabH1 to provide the critical fatty acid precursor butyryl-ACP for AHL synthesis. Loss of PssFabH1 reduces the diversion of butyryl-ACP to AHL, enabling the accumulation of acyl-ACP for synthesis of biosurfactants that contribute to bacterial swarming motility. We report that PssFabH1 and PssFabH2 each encode a 3-ketoacyl-acyl carrier protein synthase (KAS) III in P. syringae B728a. Whereas PssFabH2 is able to function in redirecting intermediates from ß-oxidation to fatty acid synthesis, PssFabH1 is an atypical KAS III protein that represents a new KAS III clade based on its sequence, non-involvement in cell growth, and novel role in AHL synthesis.

Asunto(s)

RESUMEN

Numerous functions in pathogenic Pectobacterium are regulated by quorum sensing (QS). Two different aiiA genes isolated from Bacillus sp. A24(aiiAA24) and Bacillus sp. DMS133(aiiADMS133) were used. Both genes encode acyl-homoserine lactonase (AiiA), which disrupts QS in Pectobacterium. To investigate the effect of different AiiAs on the inhibition of Pectobacterium carotovorum pathogenicity, two aiiA genes from different Bacillus strains were cloned and the resulting plasmids pME6863 (aiiAA24) and pME7080 (aiiADMS133) were transformed into P. carotovorum EMPCC cells. The effects of different lactonases on virulence features such as enzymatic activity, twitching and swimming motilities, and production of pellicle and biofilm formation were investigated. In EMPCC/pME6863, twitching and swimming motilities, and pellicle production were significantly reduced compared with EMPCC/pME7080. Quantitative real-time PCR (qRT-PCR) was used to measure virulence gene expression in transformed cells compared with expression levels in wild-type EMPCC. The expression of peh and hrpL genes was greatly reduced in EMPCC/pME6863 compared with EMPCC/pME7080. The sequence alignment and molecular dynamic modeling of two different AiiAA24 and AiiADMS133 proteins suggested that the replacement of proline 210 from AiiAA24 to serine in AiiADMS133 caused the reduction of enzyme activity in AiiADMS133.

Asunto(s)

RESUMEN

Acyl-homoserine lactones (AHLs), mediating pivotal physiological activities through quorum sensing (QS), have conventionally been considered limited to Gram-negative bacteria. However, few reports on the existence of AHLs in Gram-positive bacteria have questioned this conception. Streptomyces, as Gram-positive bacteria already utilizing a lactone-based QS molecule (i.e., gamma-butyrolactones), are yet to be explored for producing AHLs, considering their metabolic capacity and physiological distinction. In this regard, our study examined the potential production of AHLs within Streptomyces by deploying HPLC-MS/MS methods, which resulted in the discovery of multiple AHL productions by S. griseus, S. lavendulae FRI-5, S. clavuligerus, S. nodosus, S. lividans, and S. coelicolor A3(2). Each of these Streptomyces species possesses a combination of AHLs of different size ranges, possibly due to their distinct properties and regulatory roles. In light of additional lactone molecules, we further confirm that AHL- and GBL-synthases (i.e., LuxI and AfsA enzyme families, respectively) and their receptors (i.e., LuxR and ArpA) are evolutionarily distinct. To this end, we searched for the components of the AHL signaling circuit, i.e., AHL synthases and receptors, in the Streptomyces genus, and we have identified multiple potential LuxI and LuxR homologs in all 2,336 Streptomyces species included in this study. The 6 Streptomyces of interest in this study also had at least 4 LuxI homologs and 97 LuxR homologs. In conclusion, AHLs and associated gene regulatory systems could be more widespread within the prokaryotic realm than previously believed, potentially contributing to the control of secondary metabolites (e.g., antibiotics) and their complex life cycle, which leads to substantial industrial and clinical applications.

RESUMEN

Ruminants possess a specialized four-compartment forestomach, consisting of the reticulum, rumen, omasum, and abomasum. The rumen, the primary fermentative chamber, harbours a dynamic ecosystem comprising bacteria, protozoa, fungi, archaea, and bacteriophages. These microorganisms engage in diverse ecological interactions within the rumen microbiome, primarily benefiting the host animal by deriving energy from plant material breakdown. These interactions encompass symbiosis, such as mutualism and commensalism, as well as parasitism, predation, and competition. These ecological interactions are dependent on many factors, including the production of diverse molecules, such as those involved in quorum sensing (QS). QS is a density-dependent signalling mechanism involving the release of autoinducer (AIs) compounds, when cell density increases AIs bind to receptors causing the altered expression of certain genes. These AIs are classified as mainly being N-acyl-homoserine lactones (AHL; commonly used by Gram-negative bacteria) or autoinducer-2 based systems (AI-2; used by Gram-positive and Gram-negative bacteria); although other less common AI systems exist. Most of our understanding of QS at a gene-level comes from pure culture in vitro studies using bacterial pathogens, with much being unknown on a commensal bacterial and ecosystem level, especially in the context of the rumen microbiome. A small number of studies have explored QS in the rumen using 'omic' technologies, revealing a prevalence of AI-2 QS systems among rumen bacteria. Nevertheless, the implications of these signalling systems on gene regulation, rumen ecology, and ruminant characteristics are largely uncharted territory. Metatranscriptome data tracking the colonization of perennial ryegrass by rumen microbes suggest that these chemicals may influence transitions in bacterial diversity during colonization. The likelihood of undiscovered chemicals within the rumen microbial arsenal is high, with the identified chemicals representing only the tip of the iceberg. A comprehensive grasp of rumen microbial chemical signalling is crucial for addressing the challenges of food security and climate targets.

RESUMEN

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.

Asunto(s)

RESUMEN

IMPORTANCE: The mechanisms used by various bacteria to determine whether their density is sufficient to meet the QS threshold, how stringently bacterial cells block QS initiation until the QS threshold is reached, and the impacts of low-density bacterial cells encountering conditions that exceed the QS threshold are longstanding gaps in QS research. We demonstrated that translational control of the QS signaling biosynthetic gene creates a stringent QS threshold to maintain metabolic balance at low cell densities. The emergence of non-cooperative cells underlines the critical role of stringent QS modulation in maintaining the integrity of the bacterial QS system, demonstrating that a lack of such control can serve as a selection pressure. The fate of quorum-calling cells exposed to exceeding the QS threshold clarifies QS bacteria evolution in complex ecosystems.

Asunto(s)

RESUMEN

IMPORTANCE: Bacteria known as pink-pigmented facultative methylotrophs colonize many diverse environments on earth, play an important role in the carbon cycle, and in some cases promote plant growth. However, little is known about how these organisms interact with each other and their environment. In this work, we identify one of the chemical signals commonly used by these bacteria and discover that this signal controls swarming motility in the pink-pigmented facultative methylotroph Methylobacterium fujisawaense DSM5686. This work provides new molecular details about interactions between these important bacteria and will help scientists predict these interactions and the group behaviors they regulate from genomic sequencing information.

Asunto(s)