Ecological roles and release patterns of acylated homoserine lactones in Pseudomonas sp. HF-1 and their implications in bacterial bioaugmentation

Regulation and application of quorum sensing on anaerobic digestion system

Quorum sensing (QS) plays an important role in the social behavior of microbial communities. Anaerobic digestion (AD) is a biological process using anaerobic microorganisms to degrade organic macromolecules into small molecules for biogas and biofertilizer production. In AD, the QS signaling molecule N-acyl homoserine lactones (AHLs) induces bacterial metabolism, improving AD process efficiency. However, there are fewer systematic reports about QS regulation of microbial behavior in AD. In this report, the effects of signaling molecules on extracellular polymer secretion, biofilm formation, granulation of granular sludge and bacterial metabolism in AD were investigated in detail. At present, the regulation behavior of QS on AD is a group phenomenon, and there are few in-depth studies on the regulation pathway. Therefore, we conducted an in-depth analysis of the pure culture system, granular sludge and reactor in the AD. Then we pointed out that the future application potential of QS in the AD may be combined with quorum quenching (QQ) and omics technology, which is of great significance for the future application of AD.

Facilitating nitrification and biofilm formation of Vibrio sp. by N-acyl-homoserine lactones in high salinity environment

The N-acyl-homoserine lactones (AHLs)-mediated quorum-sensing (QS) system played a crucial role in regulating biological nitrogen removal and biofilm formation. However, the regulatory role of AHLs on nitrogen removal bacteria in high salinity environment has remained unclear. This study evaluated the roles and release patterns of AHLs in Vibrio sp. LV-Q1 under high salinity condition. Results showed that Vibrio sp. primarily secretes five AHLs, and the AHLs activity is strongly correlated with the bacterial density. Exogenous C10-HSL and 3OC10-HSL were found to significantly enhance ammonium removal, while making a minor contribution to the growth rate. Both the C10-HSL and 3OC10-HSL promoted the biofilm formation of Vibrio sp. with an enhancement of 1.64 and 1.78 times, respectively. The scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) observations confirmed the biofilm-enhancing effect of AHLs. Further analysis revealed that AHLs significantly improved bacterial self-aggregation and motility, as well as the level of extracellular polymeric substances (EPS). These findings provide significant guidance on construction of nitrification system at high salinity.

Influence of bioaugmentation in crude oil contaminated soil by Pseudomonas species on the removal of total petroleum hydrocarbon

This study aimed to carry out the bioaugmentation of crude oil/motor oil contaminated soil. The mixture of novel strains Pseudomonas aeruginosa PP3 and Pseudomonas aeruginosa PP4 were used in this bioaugmentation studies. The four different bioaugmentation systems (BS 1-4) were carried out in this experiment labelled as BS 1 (Crude oil contaminated soil), BS 2 (BS 1 + bacterial consortia), BS 3 (Motor oil sludge contaminated soil), and BS 4 (BS 3 + bacterial consortia). The total petroleum hydrocarbon (TPH) was investigated for monitor the effectiveness of bioaugmentation process. The highest TPH removal rate was recorded on BS 4 (9091 mg Kg ^-1) was about 67% followed by 52% on BS 2 (8584 mg Kg ^-1) respectively. The percentage of biodegradation efficiency (BE) of residual crude and motor oil contaminated soil were evaluated by GCMS analysis and the results showed that 65% (BS 2) and 83% (BS 4) respectively. Further the bioaugmented soil was subjected to the plant cultivation (Lablab purpureus) and the results revealed that the L. purpureus was rapidly grown in the systems BS 4 and BS 2 than the system BS 1 and BS 2 which was due to the lesser biodegradation of the crude oil contents. In resultant, it can be concluded that the soil was suitable for the cultivation of plant. Overall, this study revealed that the selected bacterial consortia were effectively degraded the hydrocarbon and act as a potential bioremediator in the hydrocarbon polluted soil in a short period.

Application oriented bioaugmentation processes: Mechanism, performance improvement and scale-up

Bioaugmentation is an optimization method with great potential to improve the treatment effect by introducing specific strains into the biological treatment system. In this study, a comprehensive review of the mechanism of bioaugmentation from the aspect of microbial community structure, the optimization methods facilitating application as well as feasible approaches of scale-up application has been provided. The different contribution of indigenous and exogenous strains was critically analyzed, the relationship between microbial community variation and system performance was clarified. Operation regulation and immobilization technologies are effective methods to deal with the possible failure of bioaugmentation. The gradual expansion from lab-scale, pilot scale to full-scale, the transformation and upgrading of wastewater treatment plants through the combination of direct dosing and biofilm, and the application of side-stream reactors are feasible ways to realize the full-scale application. The future challenges and prospects in this field were also proposed.

Attenuation effects of iron on dissemination of antibiotic resistance genes in anaerobic bioreactor: Evolution of quorum sensing, quorum quenching and dynamics of community composition

Zero valent iron (ZVI) coupled with bioreactors is arising as a promising technology for antibiotic resistance genes (ARGs) mitigation, whereas the succession and behaviors of microbes caused by ZVI in relieving ARGs propagation remain unclear. Herein, the effects of ZVI on microbial quorum sensing (QS), quorum quenching (QQ) system and community dynamics were examined in anaerobic bioreactor fed with oxytetracycline (tet), to illustrate the roles of evolutive microbial communication and community composition in ARGs attenuation. With the addition of 5 g/L ZVI, the total absolute abundance of tet ARGs was retarded by approximate 95% and 72% in sludge and effluent after 25 days operation. The abundance of mobile genetic elements and the heredity of antibiotic resistant bacteria revealed the declined horizontal and vertical transfer of ARGs, which directly led to the reduced ARGs propagation. Potential mechanisms are that the positive effects of ZVI on QQ activity via the functional bacteria enrichment inhibited QS system and thus ARGs transfer. Partial least--squares path modeling further demonstrated that ARGs abundance was strongly limited by the dynamics of bacterial composition and thereby less frequent microbial communication. These results provide new insights into the mechanisms of antibiotic resistome remission in anaerobic bioreactor modified by ZVI.

N-acyl-l-homoserine lactones release and microbial community changes in response to operation temperature in an anammox biofilm reactor

A 1 L lab-scale anaerobic ammonium oxidation (anammox) biofilm reactor with nitrogen loading rate of 0.11 g/L d was run for 110 days with the operation temperature declining from 36 °C to 15 °C. The total inorganic nitrogen removal efficiency showed a reduction from 80% to 66%, when the temperature declined from 36 °C to 15 °C. N-acyl-_l-homoserine lactones (AHLs) concentrations, especially C8-HSL and C6-HSL, declined in both water and biomass phases, and this decline indicated that the quorum sensing weakened. Microbial community analysis revealed that Candidatus Kuenenia was the predominant anammox bacteria during the entire operating period. The abundance of Candidatus Kuenenia increased from 1.43% to 22.89% when the temperature decreasing from 36 °C to 15 °C. The correlation between microbial genus and AHLs was complicated. Overall, the temperature decrease weakened the quorum sensing so that the nitrogen removal performance deteriorated, and increasing the anammox activity might be an efficient way to improve performance.

Dynamic characteristics of AHLs-secreting strain Aeromonas sp. A-L2 and its bioaugmentation during quinoline biodegradation

AIMS

In order to probe a more environmentally friendly method of pollutant treatment based on microbial bioaugmentation and quorum sensing (QS) effects.

METHODS AND RESULTS

The dynamic characteristics and QS effects of the acylated homoserine lactones (AHLs)-secreting strain Aeromonas sp. A-L2 (A-L2), which was isolated from the activated sludge system, was discussed. According to the liquid chromatography-mass spectrometry results, N-butyryl-homoserine lactone (C4-HSL) and N-hexanoyl-homoserine lactone (C6-HSL) were the major AHLs secreted by strain A-L2, and the swarming of strain Ochrobactrum sp. LC-1 (LC-1) was induced by these compounds. The extracellular polymeric substance secretion of the strain LC-1 was mainly led by C6-HSL, and the biofilm formation ability was mainly influenced by C6-HSL or C4-HSL (60 μg l^-1 ). The optimal AHLs secretion conditions of strain A-L2 were also studied. Drawing support from the AHLs-secreting strain A-L2 during quinoline degradation by strain LC-1, the degradation time was greatly shortened.

CONCLUSIONS

Hence, AHLs-secreting strain A-L2 can be useful as an AHLs continuous supplier during bioaugmentation and pollutant biodegradation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The bioaugmentation process of strain A-L2 on quinoline biodegradation based on QS effects would lay a certain theoretical and practical significance for large-scale applications.

Mixture of different Pseudomonas aeruginosa SD-1 strains in the efficient bioaugmentation for synthetic livestock wastewater treatment

Strains selection for inoculation is the key to the successful construction of a bioaugmentation system, a promising strategy for specific pollutant removal. Pseudomonas aeruginosa SD-1 wild-type (WT) strain exhibited high capacity for biofilm formation but low efficiency for nitrate (NO₃^-) removal. Meanwhile, quorum sensing deficient strain ΔlasR showed excellent efficiency for NO₃^- removal but poor capability for colonization in activated sludge. The opposite effect of biofilm formation and NO₃^- removal exist in WT or ΔlasR, which limits the construction of bioaugmentation system of strain SD-1 and its application. To solve this issue, a mixture of WT and ΔlasR (v/v = 1:1) was used to construct a bioaugmentation system. Compared with the inoculation of WT or ΔlasR alone, the mixed inoculation not only was beneficial for activated sludge development but also for pollutant removal. The indicators for activated sludge including the abundance of P. aeruginosa, the sludge volume index and the average particle size in mixed inoculated reactors were close to those of reactors with single and repeated inoculation of WT. The effluent of chemical oxygen demand (COD) and NO₃^--N were stable at 3.9-22.6 mg L^-1 and 0-5.53 mg L^-1 after d 3, respectively. This study presents a detailed case on the ecological tradeoff of colonization and pollutant removal of inoculated strains during bioaugmentation. The results provide information on the appropriate conditions for application of P. aeruginosa SD-1 for livestock wastewater treatment and further enrich our ecological understanding of bioaugmentation.

AHLs Regulate Biofilm Formation and Swimming Motility of Hafnia alvei H4

The aim of this study was to evaluate the role of N-acyl homoserine lactones (AHLs) in the regulation of swimming motility of Hafnia alvei H4 and its biofilm formation on 96-well plate, glass and stainless-steel surfaces. The luxI gene, which codes for an enzyme involved in AHL synthesis, was deleted to generate a luxI mutant (ΔluxI). The mutant produced no AHL, and the relative expression of the luxR gene was significantly (P < 0.05) decreased. In addition, qRT-PCR analysis showed that the relative expression of the luxR gene in ΔluxI was stimulated by the presence of exogenous AHLs (C4-HSL, C6-HSL, and 3-o-C8-HSL) added at concentrations ranging from of 50–250 μg/ml. Among the three AHLs, C6-HSL had the strongest effect. The ability of ΔluxI to form biofilm on 96-well plate, glass and stainless-steel surfaces was significantly reduced (P < 0.05) compared with the wild type (WT), but was increased when provided with 150 μg/ml C4-HSL, whereas C6-HSL and 3-o-C8-HSL had no effect. Scanning electron microscopy analysis of the biofilm revealed less bacteria adhering to the surface of stainless-steel and fewer filaments were found binding to the cells compared with the WT. Furthermore, ΔluxI also exhibited significant (P < 0.05) decrease in the expression of biofilm- and swimming motility-related genes, flgA, motA and cheA, consistent with the results observed for biofilm formation and swimming motility. Taken together, the results suggested that in H. alvei H4, C4-HSL may act as an important molecular signal through regulating the ability of the cells to form biofilm, as well as through regulating the swimming motility of the cell, and this could provide a new way to control these phenotypes of H. alvei in food processing.

Quorum sensing system and influence on food spoilage in Pseudomonas fluorescens from turbot

The spoilage of aquatic products is mainly caused by the bacterial growth, and the specific spoilage organism (SSO) plays an important role. Quorum sensing (QS) is a microbial cell-cell communication system which is coordinated with the population density, and is controlled by N-acyl-homoserine lactone (AHLs) as the Gram-negative bacteria communication signals. In this study, the SSO was Pseudomonas fluorescens (PF-04), isolated from the turbot (Scophthalmus maximus L.) during aerobically refrigerated storage. The supernatant extract of PF-04 tested the AHLs activities utilizing biosensor Chromobacterium violaceum CV026. AHL production was influenced by the environment temperature, and AHL production reduced obviously at 10 °C compare with 25 °C. In Luria-Bertani (LB) supplemented with 0.5-1.0% NaCl, AHL production reached the maximum. The AHL production was also regulated by pH of culture medium, acidic condition was conducive to persistent existence of the AHL molecules, but the alkaline environment would cause chemically unstable of AHL molecules. QS system in P. flurosecens played an imperative role in biofilm formation, protease and siderophore production. AHLs could regulate above three factors in PF-04. In summary, this study showed that (1) the influence of different environmental conditions (temperature, NaCl and pH) on AHL production revealed the correlation of QS in foods and (2) that proved the effect of external AHLs to regulate the biofilm formation, protease and siderophore production in PF-04.

Determination of quorum-sensing signal substances in water and solid phases of activated sludge systems using liquid chromatography-mass spectrometry

The detection of acyl homoserine lactones (AHLs) in activated sludge is essential for clarifying their function in wastewater treatment processes. An LC-MS/MS method was developed for the detection of AHLs in both the aqueous and solid phases of activated sludge. In addition, the effects of proteases and extracellular polymeric substances (EPS) on the detection of AHLs were evaluated by adding protease inhibitors and extracting EPS, respectively. Recoveries of each AHL were improved by adding 50μL of protease inhibitor, and recoveries were also improved from 0 to 56.9% to 24.2%-105.8% by EPS extraction. Applying the developed method to determine the type and concentration of AHLs showed that C₄-HSL, C₆-HSL, C₈-HSL and 3-oxo-C₈-HSL were widely detected in a suspended activated sludge system. The dominant AHL was C₈-HSL, with a highest concentration of 304.3ng/L. C₄-HSL was mainly distributed in the aqueous phase, whereas C₆-HSL, C₈-HSL and 3-oxo-C₈-HSL were preferentially distributed in the sludge phase.

Regulation of Nicotine Tolerance by Quorum Sensing and High Efficiency of Quorum Quenching Under Nicotine Stress in Pseudomonas aeruginosa PAO1

Quorum sensing (QS) regulates the behavior of bacterial populations and promotes their adaptation and survival under stress. As QS is responsible for the virulence of vast majority of bacteria, quorum quenching (QQ), the interruption of QS, has become an attractive therapeutic strategy. However, the role of QS in stress tolerance and the efficiency of QQ under stress in bacteria are seldom explored. In this study, we demonstrated that QS-regulated catalase (CAT) expression and biofilm formation help Pseudomonas aeruginosa PAO1 resist nicotine stress. CAT activity and biofilm formation in wild type (WT) and ΔrhlR strains are significantly higher than those in the ΔlasR strain. Supplementation of ΔlasI strain with 3OC12-HSL showed similar CAT activity and biofilm formation as those of the WT strain. LasIR circuit rather than RhlIR circuit is vital to nicotine tolerance. Acylase I significantly decreased the production of virulence factors, namely elastase, pyocyanin, and pyoverdine under nicotine stress compared to the levels observed in the absence of nicotine stress. Thus, QQ is more efficient under stress. To our knowledge, this is the first study to report that QS contributes to nicotine tolerance in P. aeruginosa. This work facilitates a better application of QQ for the treatment of bacterial infections, especially under stress.

Biofilm activity, ammonia removal and cell growth of the heterotrophic nitrifier,Acinetobactersp., facilitated by exogenousN-acyl-homoserine lactones

In the present study, the heterotrophic nitrification–aerobic denitrification strain, Acinetobacter sp. JQ1004, was treated with three typical N-acyl-homoserine lactone (AHL) molecules (C6-HSL, C8-HSL, and 3-oxo-C10-HSL) during the nitrogen removal process. The effects of AHLs on biofilm formation, flocculation, extracellular polymeric substance characteristics, and nitrogen removal were investigated. Findings revealed that low concentrations of these three AHLs could promote ammonia removal and cell growth as follows: C8-HSL > C6-HSL > 3-oxo-C10-HSL, whereas high concentrations suppressed nitrogen removal. Transcript levels of the amoA gene in the heterotrophic nitrification process were detected by real-time PCR, indicating that the addition of each AHL with 10 nmol L⁻¹ could stimulate expression of amoA. Notably, the addition of C6-HSL at relative lowly concentrations significantly accelerated biofilm formation and self-aggregation of strain JQ1004. Many microbial-flocs were observed between cells using scanning electron microscopy when strains were dosed with 10 nmol L⁻¹ C6-HSL. Excitation emission matrix spectra revealed that the addition of C6-HSL and C8-HSL at 10 nmol L⁻¹ did not change the components and structures of the extracellular polymeric substance (EPS), but the fluorescence intensity of various components increased substantially. However, the addition of 3-oxo-C10-HSL reduced the fluorescence strength of EPS, which had no remarkable effect on biofilm formation, self-aggregation, and nitrogen removal of the strain.

In the present study, the heterotrophic nitrification–aerobic denitrification strain, Acinetobacter sp. JQ1004, was treated with three typical N-acyl-homoserine lactone (AHL) molecules (C6-HSL, C8-HSL, and 3-oxo-C10-HSL) during the nitrogen removal process.

The effect of organic shock loads on the stability of anaerobic granular sludge

This study investigated the effect of organic shock loads on the stability of anaerobic granular sludge (AnGS). At double and triple shock intensity (8 and 12 kg COD/m³d organic loading rate (OLR), respectively), the accumulation of volatile fatty acids resulted in the decreasing pH of the reactors. The unstable performances of AnGS also appeared in the macroscopic properties, including the decreasing contents of relative hydrophobicity (RH), granular strength and diameter, and the fluctuation of EPS production. Noteworthily, the contents of loosely bound and tightly bound polysaccharide increased obviously and were higher than that in the control under double and triple OLR shock load. However, the growing trend of protein content was only found in the double OLR shock reactor. In addition, the N-hexanoyl-homoserine lactone (C6-HSL) content increased following the shock and then decreased during the recovery. The autoinducer-2 (AI-2) content gradually decreased under OLR shock conditions, and then rapidly increased during the recovery phase. The behaviour of the diffusible signal factor (DSF) was opposite that of AI-2. The combination of C6-HSL, AI-2 and DSF had a degraded effect on the properties of AnGS. The results provide a new reference for further research into the inter-effects among multiple signal molecules in anaerobic sludge.

ABBREVIATIONS

3-oxo-C6-HSL: N-3-oxo-hexanoyl-homoserine lactone; AHLs: acyl-homoserine lactone; AI-2: auto-inducers-2; AnGS: anaerobic granular sludge; C4-HSL: N-hydroxybutanoyl-homoserine lactone; C6-HSL: N-hexanoyl-homoserine lactone; COD: chemical oxygen demand; DSF: diffusible signal factor; EPS: extracellular polymeric substance; HPLC: High-performance liquid chromatography; HRT: hydraulic retention time; IC: integrity coefficient; LB-: loosely bound; MLSS: mixed liquor suspended solids; MLVSS: mixed liquor volatile suspended solids; OLR: organic loading rate; PN: protein; PS: polysaccharide; QS: quorum sensing; RH: Relative hydrophobicity; SS: suspended solids; TB-: tightly bound; UPLC-MS/MS: ultra-performance liquid chromatography-tandem mass spectrometry; VFAs: volatile fatty acids.

Nitrogen Source Stabilization of Quorum Sensing in the Pseudomonas aeruginosa Bioaugmentation Strain SD-1

Pseudomonas aeruginosa SD-1 is efficient at degrading aromatic compounds and can therefore contribute to the bioremediation of wastewater. P. aeruginosa uses quorum sensing (QS) to regulate the production of numerous secreted "public goods." In wastewater bioaugmentation applications, there are myriad nitrogen sources, and we queried whether various nitrogen sources impact the stabilities of both QS and the bacterial populations. In a laboratory strain of P. aeruginosa, PAO1, the absence of a nitrogen source has been shown to destabilize these populations through the emergence of QS mutant "cheaters." We tested the ability of SD-1 to grow in casein broth, a condition that requires QS for growth, when the nitrogen source with either NH₄Cl, NaNO₃, or NaNO₂ or with no added nitrogen source. There was great variability in susceptibility to invasion by QS mutant cheaters and, by extension, the stability of the SD-1 population. When grown with NH₄Cl as an extra nitrogen source, no population collapse was observed; by contrast, two-thirds of cultures grown in the presence of NaNO₂ collapsed. In the populations that collapsed, the frequency of social cheaters exceeded 40%. NaNO₃ and NaNO₂ directly favor QS mutants of P. aeruginosa SD-1. Although the mechanism by which these nitrogen sources act is not clear, these data indicate that the metabolism of nitrogen can affect the stability of bacterial populations, an important observation for continuing industrial applications with this species.IMPORTANCE Bioaugmentation as a method to help remediate wastewater pollutant streams holds significant potential to enhance traditional methods of treatment. Addition of microbes that can catabolize organic pollutants can be an effective method to remove several toxic compounds. Such bioaugmented strains of bacteria have been shown to be susceptible to competition from the microbiota that are present in wastewater streams, limiting their potential effectiveness. Here, we show that bioaugmentation strains of bacteria might also be susceptible to invasion by social cheaters and that the nitrogen sources available in the wastewater might influence the ability of cheaters to overtake the bioaugmentation strains. Our results imply that control over the nitrogen sources in a wastewater stream or selective addition of certain nitrogen sources could help stabilize bioaugmentation strains of bacteria.

Exploiting extracellular polymeric substances (EPS) controlling strategies for performance enhancement of biological wastewater treatments: An overview

Extracellular polymeric substances (EPS) are present both outside of the cells and in the interior of microbial aggregates, and account for a main component in microbial aggregates. EPS can influence the properties and functions of microbial aggregates in biological wastewater treatment systems, and specifically EPS are involved in biofilm formation and stability, sludge behaviors as well as sequencing batch reactors (SBRs) granulation whereas they are also responsible for membrane fouling in membrane bioreactors (MBRs). EPS exhibit dual roles in biological wastewater treatments, and hence the control of available EPS can be expected to lead to changes in microbial aggregate properties, thereby improving system performance. In this review, current updated knowledge with regard to EPS basics including their formation mechanisms, important properties, key component functions as well as sub-fraction differentiation is given. EPS roles in biological wastewater treatments are also briefly summarized. Special emphasis is laid on EPS controlling strategies which would have the great potential in promoting microbial aggregates performance and in alleviating membrane fouling, including limitation strategies (inhibition of quorum sensing (QS) systems, regulation of environmental conditions, enzymatic degradation of key components, energy uncoupling etc.) and elevation strategies (enhancement of QS systems, addition of exogenous agents etc.). Those strategies have been confirmed to be feasible and promising to enhance system performance, and they would be a research niche that deserves further study.

Responses of the Microalga Chlorophyta sp. to Bacterial Quorum Sensing Molecules (N-Acylhomoserine Lactones): Aromatic Protein-Induced Self-Aggregation

Bacteria and microalgae often coexist during the recycling of microalgal bioresources in wastewater treatment processes. Although the bacteria may compete with the microalgae for nutrients, they could also facilitate microalgal harvesting by forming algal-bacterial aggregates. However, very little is known about interspecies interactions between bacteria and microalgae. In this study, we investigated the responses of a model microalga, Chlorophyta sp., to the typical quorum sensing (QS) molecules N-acylhomoserine lactones (AHLs) extracted from activated sludge bacteria. Chlorophyta sp. self-aggregated in 200 μm bioflocs by secreting 460-1000 kDa aromatic proteins upon interacting with AHLs, and the settling efficiency of Chlorophyta sp. reached as high as 41%. However, Chlorophyta sp. cells were essentially in a free suspension in the absence of AHLs. Fluorescence intensity of the aromatic proteins had significant (P < 0.05) relationship with the Chlorophyta sp. settleability, and showed a positive correlation, indicating that aromatic proteins helped aggregate microalga. Transcriptome results further revealed up-regulation of synthesis pathways for aromatic proteins from tyrosine and phenylalanine that was assisted by anthranilate accumulation. To the best of our knowledge, this is the first study to confirm that eukaryotic microorganisms can sense and respond to prokaryotic QS molecules.

The Systematic Investigation of the Quorum Sensing System of the Biocontrol Strain Pseudomonas chlororaphis subsp. aurantiaca PB-St2 Unveils aurI to Be a Biosynthetic Origin for 3-Oxo-Homoserine Lactones

The shoot endophytic biocontrol strain Pseudomonas chlororaphis subsp. aurantiaca PB-St2 produces a wide range of exoproducts, including enzymes and antibiotics. The production of exoproducts is commonly tightly regulated. In order to get a deeper insight into the regulatory network of PB-St2, the strain was systematically investigated regarding its quorum sensing systems, both on the genetic and metabolic level. The genome analysis of PB-St2 revealed the presence of four putative acyl homoserine lactone (AHL) biosynthesis genes: phzI, csaI, aurI, and hdtS. LC-MS/MS analyses of the crude supernatant extracts demonstrated that PB-St2 produces eight AHLs. In addition, the concentration of all AHL derivatives was quantified time-resolved in parallel over a period of 42 h during the growth of P. aurantiaca PB-St2, resulting in production curves, which showed differences regarding the maximum levels of the AHLs (14.6 nM– 1.75 μM) and the production period. Cloning and heterologous overexpression of all identified AHL synthase genes in Escherichia coli proved the functionality of the resulting synthases PhzI, CsaI, and AurI. A clear AHL production pattern was assigned to each of these three AHL synthases, while the HdtS synthase did not lead to any AHL production. Furthermore, the heterologous expression study demonstrated unequivocally and for the first time that AurI directs the synthesis of two 3-oxo-AHLs.

Biofilm activity and sludge characteristics affected by exogenous N-acyl homoserine lactones in biofilm reactors

This study verified the effect of N-acyl homoserine lactone (AHL) concentrations on mature biofilm systems. Three concentrations of an AHL mixture were used in the batch test. Introducing of 5nM AHLs significantly increased biofilm activity and increased sludge characteristics, which resulted in better pollutant removal performance, whereas exogenous 50nM and 500nM AHLs limited pollutant removal, especially COD and nitrogen removal. To further identify how exogenous signal molecular affects biofilm system nitrogen removal, analyzing of nitrifying bacteria through real-time polymerase chain reaction (RT-PCR) revealed that these additional signal molecules affect nitrifying to total bacteria ratio. In addition, the running state of the system was stable during 15days of operation without an AHL dose, which suggests that the changes in the system due to AHL are irreversible.

Role of N-acyl-homoserine lactone (AHL) based quorum sensing on biofilm formation on packing media in wastewater treatment process

Quorum sensing (QS) signaling has been extensively studied in granules and single species populations.

Cell adhesion, ammonia removal and granulation of autotrophic nitrifying sludge facilitated by N-acyl-homoserine lactones

In this study, six N-acyl-homoserine lactone (AHL) molecules (C6-HSL, C8-HSL, C10-HSL, 3-oxo-C6-HSL, 3-oxo-C8-HSL and 3-oxo-C10-HSL) were each dosed into a bioreactor and seeded using autotrophic nitrifying sludge (ANS). The effects of the AHLs on cell adhesion, nitrification and sludge granulation were investigated. The results indicated that the efficiencies of cell adhesion and ammonia removal both had a close correlation with the side chain length and β position substituent group of the AHLs. The best-performing AHL in terms of accelerating bacterial attached-growth was 3-oxo-C6-HSL, whereas C6-HSL outperformed the others in terms of the ammonia degradation rate. The addition of 3-oxo-C6-HSL or C6-HSL increased the biomass growth rate, microbial activity, extracellular proteins and nitrifying bacteria, which can accelerate the formation of nitrifying granules. Consequently, selecting AHL molecules that could improve bacteria in attached-growth mode and nitrification efficiency simultaneously will most likely facilitate the rapid granulation of nitrifying sludge.

A sustainable method for effective regulation of anaerobic granular sludge: artificially increasing the concentration of signal molecules by cultivating a secreting strain

This study introduces sustainable quorum sensing (QS) granulation for anaerobic granular sludge (AnGS) and investigates the efficiency of three types of signal molecules on regulating AnGS granulation. The signal molecules of a secreting strain cultured in a QS regulating reactor increased their concentrations in an expanded granular sludge bed reactor throughout the granulating process. Increasing content of autoinducer-2 (AI-2) strengthened interspecific QS communication and gave a best performance with larger granular diameters, higher extracellular polymeric substance (EPS) production and relative hydrophobicity (RH). N-butyryl-homoserine lactone (C4-HSL) QS regulation was also favorable for granular growth, but its regulation was less than that of AI-2-QS. The AnGS granulated under these two types of QS regulations guided more filamentous bacteria to take part in granulation. Under diffusible signal factor (DSF)-QS regulation, the sludge had a lower granular level with a smaller granule diameter, lower EPS production (RH) when compared that of control medium.

The use of (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone for controlling acid mine drainage through the inhibition of Acidithiobacillus ferrooxidans biofilm formation

The aim of this study was to determine whether acid mine drainage (AMD) production can be decreased by (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone (furanone C-30) in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans). The effects of furanone C-30 on A. ferrooxidans biofilm production were determined by crystal violet staining and confocal laser scanning microscopy (CLSM). Biofilm-related gene expression was investigated using real-time RT-PCR. Finally, the effects of furanone C-30 on AMD production were evaluated. The results show that furanone C-30 inhibits the production of extracellular polymeric substances (EPS) and biofilm formation and significantly down-regulates the expression of biofilm-related genes. The decreased EPS production led to reduced pentlandite attachment and biofilm formation on pentlandite. Furthermore, the dissolution of both nickel and copper were inhibited by furanone C-30 without new acid formation. This study provides a promising biochemical method to control AMD.

Nicotine-degrading microorganisms and their potential applications

Nicotine-degrading microorganisms (NDMs) are a special microbial group which can use nicotine as the sole carbon and nitrogen source for growth. Since the 1950s, the bioconversion of nicotine by microbes has received increasing attention, and several NDMs have been identified, such as Arthrobacter nicotinovorans, Microsporum gypseum, Pellicularia filamentosa JTS-208, and Pseudomonas sp. 41. In recent years, increasing numbers of NDMs have been isolated and identified from tobacco plantation soil, leaf, and tobacco waste. Meanwhile, the metabolic pathway and degradation mechanism of nicotine have been elucidated in several NDMs, such as A. nicotinovorans, Agrobacterium tumefaciens S33, Aspergillus oryzae, and Pseudomonas putida S16. Moreover, several NDMs have been used in improving the quality of cigarettes, treating tobacco waste, and producing valuable intermediates of nicotine. Here, we summarize the diversity, phylogenetic analysis, and potential applications of NDMs.

Evidence for existence of quorum sensing in a bioaugmented system by acylated homoserine lactone-dependent quorum quenching

The introduction of a gene, strain, or microbial consortium into an indigenous bacterial population is known as bioaugmentation. This technique has been proposed as an effective strategy for accelerating and enhancing the removal of recalcitrant and toxic compounds during wastewater treatment. In this study, three types of reactors were used to test whether quorum sensing plays an important role in bioaugmented systems. Reverse transcriptase polymerase chain reaction showed that the inoculated strain, HF-1, successfully colonized in the bioaugmented reactor. Meanwhile, no HF-1 colonization was observed in the quorum-quenching and non-bioaugmented reactors. Removal of nicotine in the bioaugmented reactor was almost 100%, and removal of total organic carbon (TOC) was higher than 50%. However, less than 20% of nicotine and 30% of TOC was removed in quorum-quenching and non-bioaugmented reactors. Moreover, the release of acylated homoserine lactones reached the threshold for HF-1 biofilm formation in bioaugmented reactors but not in quorum-quenching or non-bioaugmented reactors. The addition of porcine kidney acylase I, a quenching reagent, to the quorum-quenching reactor hampered the colonization of HF-1. Together, these results demonstrate that quorum sensing plays an important role in HF-1 colonization of bioaugmented systems.

N-3-Oxo-octanoyl-homoserine lactone as a promotor to improve the microbial flocculant production by an exopolysaccharide bioflocculant-producing bacterium Agrobacterium tumefaciens F2

This study showed thatAgrobacterium tumefaciensF2 can produceN-3-oxo-octanoyl-homoserine lactone (3-oxo-C8HSL), one of theN-acyl-homoserine lactone (AHL) class of microbial quorum-sensing signaling molecules.

A new method for rapid construction of a Pseudomonas sp. HF-1 bioaugmented system: accelerating acylated homoserine lactones secretion by pH regulation

Pseudomonas sp. HF-1 bioaugmented systems were operated to treat tobacco wastewater under pH 5.5 for three cycles and pH 8.0 for the rest, which was suitable for HF-1 biofilm formation. The results showed that, under pH control, the contents of 3-oxo-C6-HSL, C6-HSL and 3-oxo-C8-HSL were significantly higher than HF-1 thresholds for biofilm formation. Compared with non-pH controlled reactors, HF-1 showed greater colonization in pH controlled reactors, primarily owing to the high extracellular polymeric substances secretion induced by quorum sensing. Accordingly, high indigenous community activity and granular sludge were observed. Sludge granulation occurred from the seventh cycle, and the average diameter was greater than 400 μm. These systems were also highly efficient with nearly 100% nicotine degradation and 60% total organic carbon removal. Overall, the results indicate that pH regulation is a new and feasible method for acceleration of releasing of auto-inducers, which is beneficial to construction of HF-1 bioaugmented systems.

The role of N-acyl homoserine lactones in maintaining the stability of aerobic granules

In this study, porcine kidney acylase, as N-acyl homoserine lactones (AHLs)-degradation enzyme, was employed for the first time to directly investigate the role of AHLs in the structure stability of aerobic granules. Results clearly showed that inactivation of AHLs by AHLs-acylase could weaken the stability of aerobic granule. In the presence of AHLs-acylase, AHLs were degraded by hydrolyzing the amide linkage, which resulted in aerobic granular attachment potential and activity of AHLs-based quorum sensing significantly reduced. In addition, it was also found that inactivation of AHLs led to reduction of extracellular polysaccharides and protein (PN), especially PN, and induced extracellular polymeric substances matrix damaged, which was hostile to stability of aerobic granules. This study provided direct evidence that AHLs played a key role in improving aerobic granular stability, and a potential way to enhance long-term stability of aerobic granules.

Effect of Pseudomonas sp. HF-1 inoculum on construction of a bioaugmented system for tobacco wastewater treatment: analysis from quorum sensing

To better construct a bioaugmented system for tobacco wastewater treatment, activated sludge was inoculated with different concentrations of the nicotine-degrading bacterium Pseudomonas sp. HF-1. The results showed that inoculum concentrations of 0.55 ± 0.01 and 1.10 ± 0.03 mg/g (dry weight of strain HF-1/dry weight of activated sludge) were best to ensure strain HF-1 survival and successful bioaugmentation. The release pattern of autoinducer (AI) for quorum sensing in the bioaugmented system was also investigated. During the period of HF-1 inoculation, compared with failed bioaugmented systems, AI-2 was significantly increased in the successful systems, suggesting that AI-2-mediated bacterial communication played an important role in the colonization of HF-1. When inoculation of strain HF-1 was stopped, the amount of AI-2 decreased and leveled out in all systems. Notably, there was a greater than threefold increase of short-chain AHLs in failed bioaugmented systems, but no increase in successful ones, implying that the fluctuation of short-chain AHLs could be an indicator of the failure of bioaugmentation. Thus, AI-2-mediated quorum sensing could be implemented to facilitate HF-1 colonization.

Where are signal molecules likely to be located in anaerobic granular sludge?

Quorum sensing is a concentration-sensing mechanism that plays a vital role in sludge granulation. In this study, the regularities of distribution of different signal molecules, including intra- and interspecific signal molecules (diffusible signal factor, DSF), interspecific signal molecules (autoinducter-2, AI-2) and intraspecific signal molecules (acyl-homoserine lactones, AHLs), from three types of anaerobic granular sludge were investigated. The results showed that 70-90% of DSF was distributed in sludge, while AI-2 in the Water phase accounted for over 80% of the total content. Interestingly, there was a positive correlation between DSF and AI-2, which played opposite roles in granulation. Moreover, more than 55% of short and medium acyl chain AHLs tended to spread in aqueous water, while the long acyl chain AHLs were closer to granular sludge than the short and medium acyl chain AHLs. With the exception of one type of sludge, the percentage of long acyl chain AHLs in the sludge phase was greater than 70%. The different distributions of signal molecules were primarily determined based on their physicochemical properties, including molecular weight and solubility in water or organic solutions. In addition, the basic properties of sludge, such as the granular level or the production of EPS, were closely related to the diversity, distribution and concentration of signal molecules. As a medium in granulation, extracellular polymeric substances production was regulated by different signal molecules from different parts of anaerobic granular sludge. This study provides a foundation for investigation of quorum sensing in the system of anaerobic granular sludge.

Effects of Inoculum Amount, Initial pH, and Nicotine Load on the Set-Up of Bioaugmented System withPseudomonasSp. HF-1 to Treat Tobacco Wastewater

This study evaluated and optimized the influence of inoculum amount, initial pH, and nicotine load on the construction ofPseudomonassp. HF-1 bioaugmented system for tobacco wastewater treatment. The results demonstrated that the optimum condition for the set-up of strain HF-1 bioaugmented system was 1.10 mg/g (dry weight of strain HF-1/dry weight of activated sludge) of inoculum amount, initial pH 7.0, and 250–1000 mg/L nicotine load. Higher than 1.10 mg/g could lead to noncolonization of strain HF-1 in activated sludge and failure of set-up of this bioaugmented system. Higher than pH 8.0 could restrain the colonization of strain HF-1 in activated sludge. Even though strain HF-1 colonizes in the activated sludge when pH was above 8.0, the removal of nicotine and total organic carbon (TOC) was suppressed due to low activities of bacteria in the activated sludge. Nicotine load did not show inhibition effect on set-up of bioaugmented system, but the ability of TOC removal was restrained when the nicotine load was above 1000 mg/L. This work could offer vital parameters for the set-up of bioaugmented system to treat tobacco wastewater in engineering.

The microbial attachment potential and quorum sensing measurement of aerobic granular activated sludge and flocculent activated sludge

The aerobic granulation process is involved in the attachment of microorganisms, and the quorum sensing (QS) is supposed to play an important role in microbial attachment. In this study, the attachment potential of aerobic granular activated sludge (AGAS) and flocculent activated sludge (FAS) was investigated. Results clearly showed that AGAS had stronger attachment potential than FAS. A bioassay with NTL4 proved that N-acylhomoserine lactones (AHLs) were produced in both sludge, but the AHLs content of AGAS was significantly higher than FAS. Additionally, the extracellular polymeric substances (EPS) measurements indicated that there were more proteins and polysaccharides in the hydrophobic EPS fraction of AGAS. Besides, the bacterial community structure of AGAS differed from FAS by PCR-DGGE. Some hydrophobic bacteria, such as Flavobacterium, exclusively existed in AGAS. It was speculated that the difference of attachment potential between AGAS and FAS was derived from the divergence of AHLs, EPS and microbial community.

The effect of quorum sensing and extracellular proteins on the microbial attachment of aerobic granular activated sludge

In this study, vanillin, a quorum sensing (QS) blocker, and proteinase K were employed to investigate the effect of QS and extracellular proteins on the microbial attachment of aerobic granular activated sludge (AGAS). Results clearly showed that both vanillin and proteinase K could reduce attachment potential of AGAS, and the combined use of them was more effective in reducing attachment biomass of AGAS. The contents of N-acylhomoserine lactones (AHLs) and extracellular proteins were reduced in the presence of vanillin and proteinase K. Besides, it was found that extracellular proteins could promote microbial attachment of AGAS, and it was also revealed that AHLs-mediated QS might be involved in microbial attachment of AGAS through the regulation of extracellular proteins. This study suggested that both QS and extracellular proteins might play important roles in the development of "AGAS biofilm" from the perspective of the biofilm.

Differences between 4-fluoroaniline degradation and autoinducer release by Acinetobacter sp. TW: implications for operating conditions in bacterial bioaugmentation

To develop a bacterial bioaugmentation system for fluorine-containing industrial wastewater treatment, optimal conditions for 4-fluoroaniline (4-FA) degradation and autoinducer release in Acinetobacter sp. TW were determined. Quorum sensing in biofilms of strain TW was also investigated. Different optimal conditions exist for 4-FA degradation and autoinducer release, particularly with regard to pH. Quorum sensing modulates extracellular polymeric substance (EPS) secretion and biofilm formation in the strain but plays no role in 4-FA degradation. Under optimal conditions for 4-FA degradation, the release of N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C6-HSL) and N-hexanoyl-homoserine lactone (C6-HSL) in strain TW was significantly lower than required for quorum sensing. Under optimal conditions for autoinducer release, on the other hand, 3-oxo-C6-HSL and C6-HSL levels exceeded the quorum sensing thresholds, thereby inducing EPS secretion and biofilm formation. We conclude that the optimal conditions for autoinducer release (25 °C, pH 5, 800 mg L(-1) 4-FA, and 0 % NaCl) are suitable for bacterial colonization in bioaugmentation, while those for 4-FA degradation (25-30 °C, pH 8 and 800 mg L(-1) 4-FA) maximize the system performance after colonization.

Bioaugmentation of activated sludge with Acinetobacter sp. TW enhances nicotine degradation in a synthetic tobacco wastewater treatment system

Bioaugmentation (BA) using Acinetobacter sp. TW with high nicotine-degrading efficiency was applied in a bioreactor receiving a load of COD (3,200 ± 50 mg/L) and nicotine (1.0 ± 0.1g/L). The results showed that because of the colonization of strain TW, the COD removal was stable at 80-90%, while nicotine removal reached 98% in the BA system. Furthermore, according to PCR-DGGE fingerprinting, compared with the originally activated sludge, more bacteria existed in the BA systems while some bacteria disappeared from the non-BA system. In terms of the quorum sensing, short chain AHLs increased to assist colonization of strain TW, and long chain AHLs were secreted and helped to resist the nicotine toxicity. Compared with the non-BA system, the amounts of ROS, protein carbonyls and 8-OHdG were significant lower in the BA systems, which suggested that strain TW played an important role in eliminating the nicotine toxicity from the bioreactors.