Biodegradation of polyurethanes by Staphylococcus warneri and by microbial co-culture.

With the increasing production and use of polyurethanes (PUs), it is necessary to develop sustainable techniques for the remediation of plastic pollution. The use of microorganisms capable of biodegrading PUs may be an environmentally desirable solution for controlling these plastic contaminants. To contribute to the discovery of alternatives for the mitigation of plastics in the environment, this study aimed to explore the potential of StaphylococcuswarneriUFV_01.21, isolated from the gut of Galleria mellonellalarvae, for biodegradation of PU in pure culture and microbial co-culture with Serratia liquefaciensL135. S. warneri grew using Impranil® PU as the sole carbon source in pure culture and co-culture. With six days of incubation, the biodegradation of Impranil® in Luria Bertani broth was 96, 88 and 76%, while in minimal medium, it was 58, 54 and 42% for S. warneri, S. liquefaciens, and co-culture, respectively. In addition, S. warneri in pure culture or co-culture was able to biodegrade, adhere and form biofilms on the surfaces of Impranil® disks and poly[4,4'-methylenebis (phenyl isocyanate)-alt-1,4-butanediol/di(propylene glycol)/polycaprolactone] (PCLMDI) films. Scanning electron microscopy also revealed biodegradation by detecting the formation of cracks, furrows, pores, and roughness on the surfaces of inoculated PU, both with pure culture and microbial co-culture. This study is the first to demonstrate the potential of S. warneriin PU biodegradation.

Biodegradation of polyurethanes by Serratia liquefaciens L135 and its polyurethanase: In silico and in vitro analyses.

Polyurethanes (PUs) are found in many everyday products and their disposal leads to environmental accumulation. Therefore, there is an urgent need to develop ecologically sustainable techniques to biodegrade and recycle this recalcitrant polymer and replace traditional methods that form harmful by-products. Serratia liquefaciens L135 secretes a polyurethanase with lipase activity, and this study explores the biodegradation of PUs by this bacterium and its enzyme through in silico and in vitro analyses. PUs monomers and tetramers were constructed in silico and tested with modeled and validated structure of the polyurethanase from S. liquefaciens. The molecular docking showed that all PUs monomers presented favorable interactions with polyurethanase (values of binding energy between -84.75 and -121.71 kcal mol-1), including PU poly[4,4'-methylenebis (phenyl isocyanate)-alt-1,4-butanediol/di (propylene glycol)/polycaprolactone] (PCLMDI). Due to repulsive steric interactions, tetramers showed less favorable interactions (values between 24.26 and -45.50 kcal mol-1). In vitro analyses evaluated the biodegradation of PUs: Impranil® and PCLMDI; this latter showed high binding energy with this polyurethanase in silico. The biodegradation of Impranil® by S. liquefaciens and its partially purified polyurethanase was confirmed in agar by forming a transparent halo. Impranil® disks inoculated with S. liquefaciens and incubated at 30 °C for six days showed rupture of the PU structure, possibly due to the formation of cracks visualized by scanning electron microscopy (SEM). PCLMDI films were also biodegraded by S. liquefaciens after 60 days of incubation, with the formation of pores and cracks visualized by SEM. The biodegradation may have occurred due to the action of polyurethanase produced by this bacterium. This work provides essential information on the potential of S. liquefaciens to biodegrade PUs through in silico analyses combined with in vitro analyses.

Metal-immobilizing and urease-producing bacteria increase the biomass and reduce metal accumulation in potato tubers under field conditions.

In this study, the effect of two metal-immobilizing bacterial strains, Serratia liquefaciens CL-1 and Bacillus thuringiensis X30, on the availability of Cd and Pb and the metal accumulation in potato tubers, as well as the underlying mechanisms in metal-contaminated soils were characterized. Moreover, the impacts of the strains on metal immobilization, pH, and NH4+ concentration in metal-contaminated soil solutions were evaluated. Strains CL-1 and X30 increased tuber dry weight by 46% and 40%, reduced tuber Cd and Pb contents by 68-83% and 42-47%, and decreased the Cd and Pb translocation factors by 61-70% and 30-34%, respectively, compared to the controls. Strains CL-1 and X30 decreased the available Cd and Pb contents by 52-67% and 30-44% and increased the NH4+ content by 55% and 31%, pH, urease activity by 70% and 41%, and relative abundance of ureC gene copies by 37% and 20% in the rhizosphere soils, respectively, compared with the controls. Reduced Cd and Pb concentrations and increased pH and NH4+ concentration were found in the bacteria-inoculated soil solution compared to the controls. These results suggested that the strains reduced tuber metal uptake through decreasing the metal availability and increasing the pH, ureC gene relative abundance and urease activity as well as decreasing the metal translocation from the leaves to tubers. These results may provide an effective metal-immobilizing bacteria (especially strain CL-1)-enhanced approach to reduce metal uptake of potato tubers in metal-polluted soils.

Heavy metal-immobilizing bacteria increase the biomass and reduce the Cd and Pb uptake by pakchoi (Brassica chinensis L.) in heavy metal-contaminated soil.

Microbial immobilization is a novel and environmentally friendly technology that uses microbes to reduce metal availability in soil and accumulation of heavy metals in plants. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of pakchoi in Cd- and Pb-contaminated farmland and investigated their effects on Cd and Pb accumulation in pakchoi and the underlying mechanisms. The results showed that two urease-producing bacteria, Bacillus megaterium N3 and Serratia liquefaciens H12, were identified by screening. They had higher ability to produce urease (57.5 ms cm-1 min-1 OD600-1 and 76.4 ms cm-1 min-1 OD600-1, respectively). The two strains allowed for the immobilization of Cd and Pb by extracellular adsorption, bioprecipitation, and increasing the pH (from 6.94 to 7.05-7.09), NH4+ content (69.1%-127%), and NH4+/NO3- ratio (from 1.37 to 1.67-2.11), thereby reducing the DTPA-extractable Cd (35.3%-58.8%) and Pb (37.8%-62.2%) contents in the pakchoi rhizosphere soils and the Cd (76.5%-79.7%) and Pb (76.3%-83.5%) contents in the leaves (edible tissue) of pakchoi. The strains were highly resistant to heavy metal toxicity; produced IAA, siderophores and abscisic acid; and increased the NH4+/NO3- ratio, which might be related to the two strains protectiing pakchoi against the toxic effect of Cd and Pb and increasing pakchoi biomass. Thus, the results were supposed to strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Transcriptomic responses of Serratia liquefaciens cells grown under simulated Martian conditions of low temperature, low pressure, and CO2-enriched anoxic atmosphere.

Results from previous experiments indicated that the Gram-negative α-proteobacterium Serratia liquefaciens strain ATCC 27592 was capable of growth under low temperature (0 °C), low pressure (0.7 kPa), and anoxic, CO2-dominated atmosphere-conditions intended to simulate the near-subsurface environment of Mars. To probe the response of its transcriptome to this extreme environment, S. liquefaciens ATCC 27592 was cultivated under 4 different environmental simulations: 0 °C, 0.7 kPa, CO2 atmosphere (Condition A); 0 °C, ~101.3 kPa, CO2 atmosphere (Condition B); 0 °C, ~101.3 kPa, ambient N2/O2 atmosphere (Condition C); and 30 °C, ~101.3 kPa, N2/O2 atmosphere (Condition D; ambient laboratory conditions). RNA-seq was performed on ribosomal RNA-depleted total RNA isolated from triplicate cultures grown under Conditions A-D and the datasets generated were subjected to transcriptome analyses. The data from Conditions A, B, or C were compared to laboratory Condition D. Significantly differentially expressed transcripts were identified belonging to a number of KEGG pathway categories. Up-regulated genes under all Conditions A, B, and C included those encoding transporters (ABC and PTS transporters); genes involved in translation (ribosomes and their biogenesis, biosynthesis of both tRNAs and aminoacyl-tRNAs); DNA repair and recombination; and non-coding RNAs. Genes down-regulated under all Conditions A, B, and C included: transporters (mostly ABC transporters); flagellar and motility proteins; genes involved in phenylalanine metabolism; transcription factors; and two-component systems. The results are discussed in the context of Mars astrobiology and planetary protection.

Metabolic fingerprints of Serratia liquefaciens under simulated Martian conditions using Biolog GN2 microarrays.

Microorganisms growing at atmospheric pressures of 0.7 kPa may have a significant impact on the search for life on Mars. Data on their nutrient requirements in a simulated Martian environment are required to ascertain both the potential risk of forward contamination and the potential of past or present habitability of Mars. Serratia liquefaciens can grow at concomitant conditions of low pressure, low temperature, and anoxic atmosphere. Changes in the metabolic fingerprint of S. liquefaciens grown under varying physical conditions including diverse atmospheric pressures (0.7 kPa to 101.3 kPa), temperatures (30 °C or 0 °C), and atmospheric gas compositions (Earth or CO2) were investigated using Biolog GN2 assays. Distinct patterns for each condition were observed. Above 10 kPa S. liquefaciens performed similar to Earth-normal pressure conditions (101.3 kPa) whereas below 10 kPa shifts in metabolic patterns were observed. The differences indicated a physiological alteration in which S. liquefaciens lost its ability to metabolize the majority of the provided carbon sources at 0.7 kPa with a significant decrease in the oxidation of amino acids. By measuring the physiological responses to different carbon sources we were able to identify nutritional constraints that support cellular replication under simulated shallow Mars subsurface conditions.

Metal-immobilizing Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 increase biomass and reduce heavy metal accumulation of radish under field conditions.

In this study, metal-tolerant bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were compared for their Cd and Pb immobilization in solution and impacts on biomass and Cd and Pb uptake in a radish in metal-contaminated soils under field conditions. Strains CL-1 and X30 significantly reduced water-soluble Cd and Pb concentrations (45-67%) and increased the pH in solution compared to the controls. These strains significantly increased the biomass (25-99%) and decreased edible tissue Cd and Pb uptake in the radish (37-81%) and DTPA-extractable Cd and Pb contents (18-44%) of the rhizosphere soil compared to the un-inoculated controls. Strain CL-1 had higher potential to reduce edible tissue Cd and Pb uptake in the radish and DTPA-extractable Cd content than strain X30. Also, these strains significantly increased Cd translocation factor and strain CL-1 also significantly increased Pb translocation factor of the radish. Furthermore, strain CL-1 significantly increased the ratio of small soil aggregates (< 0.25 mm and 0.25-0.50 mm) of the rhizosphere soil. The results showed that these strains reduced the edible tissue Cd and Pb uptake through decreasing Cd and Pb availability in the soil and increasing Cd or Pb translocation from the roots to the leaves of the radish. The results also suggested the bacteria-related differences in reduced heavy metal uptake in the radish and the mechanisms involved under field conditions.

Increased biomass and reduced rapeseed Cd accumulation of oilseed rape in the presence of Cd-immobilizing and polyamine-producing bacteria.

Two Cd-immobilizing and polyamine-producing bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were characterized for their effects on Cd immobilization, pH, and polyamine production in the solution and the rapeseed biomass and Cd uptake of Brassica napus Qinyou-10 in Cd-contaminated soil. These strains significantly increased pH and reduced water-soluble Cd concentration (25-76%) compared to the controls. Furthermore, strain CL-1 produced more polyamine (71-192%) in the solution than strain X30. Cell surface absorbed Cd content was increased by 23-56% in the presence of strain CL-1 compared to strain X30. The strains significantly increased the rapeseed biomass (12-32%), pH, polyamine content (70-244%), and relative abundance (21-49%) of arginine decarboxylase-producing bacteria (ADPB) of the rhizosphere soils but decreased DTPA-extractable Cd content and rapeseed Cd uptake compared to the controls. Notably, strain CL-1 had higher ability to reduce the rapeseed Cd and DTPA-extractable Cd contents and increase the abundance of ADPB than strain X30. Our results showed the distinct impact of these strains on the rapeseed Cd uptake and available Cd content and suggested that these strains reduced the available Cd and rapeseed Cd uptake by increasing the cell adsorption of Cd, abundance of ADPB, polyamine production, and pH in the rhizosphere soils.

Microbial dynamics of model Fabriano-like fermented sausages as affected by starter cultures, nitrates and nitrites.

The present study promotes the valorization of Fabriano-like fermented sausages, which are central-Italy salami with an origin that dates to the early 17th century, for the possible future selection of autochthonous starter cultures to be used with respect to local traditions. To the best of the authors' knowledge, this study represents the first attempt to define the microbial dynamics in Fabriano-like fermented sausage and the effect of nitrates/nitrites and starter cultures on its natural bacterial biota. Culture and RNA-based techniques (RT-PCR-DGGE and Illumina sequencing) were used to assess the microbial ecology of model Fabriano-like fermented sausages together with the impact of starter cultures and different nitrate and nitrite concentrations. The meat batter was used to produce two batches of fermented sausages that were prepared as follows: i) without commercial starters or ii) with the use of starter cultures composed of Pediococcus pentosaceus and Staphylococcus xylosus. Each batch was further divided into three different batches with the addition of 0/0 mg kg-1 nitrate/nitrite, 75/60 mg kg-1 nitrate/nitrite and 150/125 mg kg-1 nitrate/nitrite to the first, second and third batch, respectively. The samples, which were produced in triplicate, were analyzed on the day of production and after 7, 21, and 42 days of ripening. Enterobacteriaceae counts were always higher in model Fabriano-like sausages produced without the use of starter cultures at all of the sampling times irrespective of the tested nitrate/nitrite concentrations. Lactobacilli counts were positively influenced by the starters, although this influence was not evident over time; moreover, the effect of nitrates and nitrites on the counts of lactobacilli differed over time. As a general trend, coagulase-negative cocci counts were apparently not influenced by the tested nitrate/nitrite concentrations. Regarding the effect of nitrates/nitrites on the microbial diversity revealed by RT-PCR-DGGE, the higher the concentration, the lower the presence of some genera/species such as Pseudomonas spp., Serratia liquefaciens and Staphylococcus spp. However, Illumina sequencing detected Pseudomonas spp. as a minority species after 7, 21 and 42 days of ripening irrespective of the nitrate/nitrite concentration. The presence of Staphylococcus species was highlighted by both RT-PCR-DGGE and Illumina sequencing at all of the stages of ripening, although its presence was massively detected in fermented sausages produced without the use of nitrates/nitrites at the end of ripening. Overall, the data collected clearly highlighted the dominance of Lactobacillus sakei in all of the fermented sausages during ripening (from day 7 to day 42) and irrespective of the nitrate/nitrite concentration and added starter cultures. Moreover, Pediococcus spp. was principally detected in model Fabriano-like fermented sausage with added starter cultures irrespective of the nitrate/nitrite concentration.

Biosynthesis of Heliotropin by a Novel Strain of Serratia liquefaciens.

The present study has been conducted towards isolation of bacteria capable of producing heliotropin via microbial conversion. Strain ZMT-1 capable of synthesizing heliotropin efficiently was obtained by enrichment culture of soil samples and a high-throughput screening method, and identified as Serratia liquefaciens. Heliotropin was identified by gas chromatography and gas chromatography-mass spectrometry analysis. In addition, the culture medium was optimized to improve heliotropin yield by experimental designs. The application of a Plackett-Burman design found that NH4NO3 and K2HPO4•3H2O have significant effects on heliotropin production. Central composite design experiments were further used to predict the optimal concentrations of NH4NO3 and K2HPO4•3H2O, which were 1.0 and 0.5 g/l, respectively. After the optimization of cultural medium, heliotropin yield was increased by 4.52-fold when compared with the unoptimized minimal medium. This study is the first to report the biosynthesis of heliotropin by S. liquefaciens. S. liquefaciens ZMT-1 can produce heliotropin efficiently, indicating its potential as one heliotropin-producing strain.

Evaluation of the spoilage potential of bacteria isolated from chilled chicken in vitro and in situ.

Microorganisms play an important role in the spoilage of chilled chicken. In this study, a total of 53 isolates, belonging to 7 species of 3 genera, were isolated using a selective medium based on the capacity to spoil chicken juice. Four isolates, namely Aeromonas salmonicida 35, Pseudomonas fluorescens H5, Pseudomonas fragi H8 and Serratia liquefaciens 17, were further characterized to assess their proteolytic activities in vitro using meat protein extracts and to evaluate their spoilage potential in situ. The in vitro studies showed that A. salmonicida 35 displayed the strongest proteolytic activity against both sarcoplasmic and myofibrillar proteins. However, the major spoilage isolate in situ was P. fragi H8, which exhibited a fast growth rate, slime formation and increased pH and total volatile basic nitrogen (TVBN) on chicken breast fillets. The relative amounts of volatile organic compounds (VOCs) originating from the microorganisms, including alcohols, aldehydes, ketones and several sulfur compounds, increased during storage. In sum, this study demonstrated the characteristics of 4 potential spoilage bacteria on chilled yellow-feather chicken and provides a simple and convenient method to assess spoilage bacteria during quality management.

Isolation of bacterial strains able to metabolize lignin and lignin-related compounds.

UNLABELLED: In this study, we identified five strains isolated from soil and sediments able to degrade kraft lignin, aromatic dyes and lignin derivatives. Using 16S rRNA gene sequencing, the isolates were identified as Serratia sp. JHT01, Serratia liquefacien PT01, Pseudomonas chlororaphis PT02, Stenotrophomonas maltophilia PT03 and Mesorhizobium sp. PT04. All the isolates showed significant growth on lignin with no water-extractable compounds. Synthetic aromatic dyes were used to assess the presence of oxidative enzymes. All the isolates were able to use the thiazine dye Methylene blue and the anthraquinone dye Remazol Brilliant Blue R as the sole carbon source. Guaiacol, veratryl alcohol and biphenyl were also mineralized by all the strains isolated. These results suggest they could be used for the treatment of aromatic pollutants and for the degradation of the lignocellulosic biomass. SIGNIFICANCE AND IMPACT OF THE STUDY: The valorization of waste lignin and lignocellulosic biomass by biocatalysis opens up new possibilities for the production of value-added substituted aromatics, biofuel and for the treatment of aromatic pollutants. Bacteria with ligninolytic potential could be a source of novel enzymes for controlled lignin depolymerization. In this work, five soil bacteria were isolated and studied. Every isolate showed significant growth on lignin and was able to degrade several lignin monomers and ligninolytic indicator dyes. They could thus be a source of novel ligninolytic enzymes as well as candidates for a bacterial consortium for the delignification of lignocellulosic biomass.

Evaluation of bioremediation potentiality of ligninolytic Serratia liquefaciens for detoxification of pulp and paper mill effluent.

Due to high pollution load and colour contributing substances, pulp and paper mill effluents cause serious aquatic and soil pollution. A lignin-degrading bacterial strain capable of decolourising Azure-B dye was identified as lignin peroxidase (LiP) producing strain LD-5. The strain was isolated from pulp and paper mill effluent contaminated site. Biochemical and 16S rDNA gene sequence analysis suggested that strain LD-5 belonged to the Serratia liquefaciens. The strain LD-5 effectively reduced pollution parameters (colour 72%, lignin 58%, COD 85% and phenol 95%) of real effluent after 144h of treatment at 30°C, pH 7.6 and 120rpm. Extracellular LiP produced by S. liquefaciens during effluent decolourisation was purified to homogeneity using ammonium sulfate (AMS) precipitation and DEAE cellulose column chromatography. The molecular weight of the purified lignin peroxidase was estimated to be ∼28kDa. Optimum pH and temperature for purified lignin peroxidase activity were determined as pH 6.0 and 40°C, respectively. Detoxified effluent was evaluated for residual toxicity by alkaline single cell (comet) gel electrophoresis (SCGE) assay using Saccharomyces cerevisiae MTCC 36 as model organism. The toxicity reduction to treated effluent was 49.4%. These findings suggest significant potential of S. liquefaciens for bioremediation of pulp and paper mill effluent.

Interaction of macrophages with a cytotoxic Serratia liquefaciens human isolate.

Macrophages play key roles in host defense by recognizing, engulfing, and killing microorganisms. Understanding the response of macrophages to pathogens may provide insights into host defenses and the tactics used by pathogens to circumvent these defenses. In the present study, we investigated the interaction between a clinical isolate of Serratia liquefaciens and macrophages. S. liquefaciens strain HUMV-3250 triggers a fast and potent cytotoxic effect upon infection. This process requires the presence of live bacteria, adherence, and protein synthesis but not phagocytosis/bacterial internalization. Moreover, cytotoxicity assays, analysis of DNA integrity, immunofluorescence, and confocal, scanning, and time-lapse microscopy revealed that macrophage viability decreased rapidly with time upon challenge, and depends on the MOI used. Treatment of macrophages with caspase-1 inhibitors, or with specific inhibitors of phagocytosis, did not alter the infection outcome. Moreover, human macrophages exhibited similar cytotoxic changes after infection with this strain. Macrophages responded to this cytotoxic strain with a robust pattern of pro-inflammatory gene expression. However, phagocytosis attempts to engulf live bacteria were unsuccessful, and the phagocytes were unable to kill the bacteria. We conclude that macrophage cell death occurs rapidly as a result of necrotic events after close contact with S. liquefaciens. These results likely have important implications for understanding Serratia pathogenesis and host response to infection.

Biodegradation and bioremediation potential of diazinon-degrading Serratia marcescens to remove other organophosphorus pesticides from soils.

The ability of diazinon-degrading Serratia marcescens to remove organophosphorus pesticides (OPPs), i.e. chlorpyrifos (CP), fenitrothion (FT), and parathion (PT) was studied in a mineral salt medium (MSM) and in three soils of different characteristics. This strain was capable of using all insecticides at concentration of 50 mg/l as the only carbon source when grown in MSM, and 58.9%, 70.5%, and 82.5% of the initial dosage of CP, FT, and PT, respectively was degraded within 14 days. The biodegradation experiment showed that autochthonous microflora in all soils was characterized by a degradation potential of all tested OPPs; however, the initial lag phases for degradation of CP and FT, especially in sandy soil, were observed. During the 42-day experiment, 45.3%, 61.4% and 72.5% of the initial dose of CP, FT, and PT, respectively, was removed in sandy soil whereas the degradation of CP, FT, and PT in the same period, in sandy loam and silty soils reached 61.4%, 79.7% and 64.2%, and 68.9%, 81.0% and 63.6%, respectively. S. marcescens introduced into sterile soils showed a higher degradation potential (5-13%) for OPPs removal than those observed in non-sterile soil with naturally occurring attenuation. Inoculation of non-sterile soils with S. marcescens enhanced the disappearance rates of all insecticides, and DT50 for CP, FT, and PT was reduced by 20.7, 11.3 and 13.0 days, and 11.9, 7.0 and 8.1 days, and 9.7, 14.5 and 12.6 days in sandy, sandy loam, and silty soils, respectively, in comparison with non-sterile soils with only indigenous microflora. This ability of S. marcescens makes it a suitable strain for bioremediation of soils contaminated with OPPs.

Profiling of N-acyl-homoserine lactones by liquid chromatography coupled with electrospray ionization and a hybrid quadrupole linear ion-trap and Fourier-transform ion-cyclotron-resonance mass spectrometry (LC-ESI-LTQ-FTICR-MS).

A method for the comprehensive profiling of the N-acyl-homoserine lactone (AHL) family of bacterial quorum-sensing molecules is presented using liquid chromatography (LC) coupled to a hybrid quadrupole linear ion trap (LTQ) and Fourier-transform ion-cyclotron-resonance mass spectrometer (FTICR). We demonstrate an increase in signal intensity in MS with electrospray ionization (ESI) of the protonated molecules, [M + H](+), by using acetonitrile (ACN) instead of methanol (MeOH) as the organic solvent under the conditions in which the samples were supplied to the probe by direct infusion at constant flow rates. The presence of ACN prevents the formation of methanol adducts such as [M + MeOH + H](+) and [M + MeOH + Na](+), while also lowering the signal intensity of sodiated [M + Na](+) ions. Sensitivity of these signaling molecules in terms of signal-to-noise ratio (S/N) using low-resolution LTQ-MS and high-resolution FTICR-MS were compared under reversed-phase (RP) LC separations with ESI interface. Special emphasis was paid to the choice of the separation column, its elution conditions and detection of the major AHL compounds produced by the Serratia liquefaciens strain ATCC 27592. The most promising results were obtained using a RP C16-amide column eluted with a linear mobile phase gradient ACN/H(2)O containing 0.1% formic acid. The whole set of AHL homologs in bacterial extracts was detected in the extracted-ion chromatographic (XIC) mode, and the calculations of molecular formulae were performed by including the isotopic pattern. This mode of displaying data, with a very narrow mass-to-charge ratio window (i.e. +/- 0.0010 as m/z unit) around each selected ion, has allowed the identification of all the eight known homoserine lactones, viz. C(4)-HSL, 3-oxo-C(6)-HSL, C(6)-HSL, 3-oxo-C(8)-HSL, C(8)-HSL, C(10)-HSL, C(12)-HSL and C(14)-HSL. In addition, at least four uncommon signaling mediators previously unreported, namely, 3-oxo-C(10:1)-HSL, 3-oxo-C(11:2)-HSL, 3-oxo-C(13:2)-HSL and 3-OH-C(16)-HSL, were identified and characterized; their roles in cell-to-cell communication has to be elucidated.