Effects of N-acyl-homoserine lactones-based quorum sensing on biofilm formation, sludge characteristics, and bacterial community during the start-up of bioaugmented reactors

Self-assembly of algal-bacterial granules induced by bacterial N-acyl-homoserine lactone variation in response to high-strength pyridine

Algal-bacterial granules (ABGs) system represents a promising technology for organic wastewater treatment due to its high settleability, efficient oxygen transfer, and low-energy consumption. However, the secretion of extracellular polymeric substances (EPS) in algae, which played a key role in self-assembly of ABGs, would be inhibited by concentrated organic wastewater. This study proposed a novel strategy for developing ABGs by inducing bacterial N-acyl-homoserine lactone (AHL) variation through high-strength pyridine application. Results showed that bacterial long-chain AHL concentrations significantly increased in response to high-strength pyridine at 550 mg L-1, inducing the secretion of algal extracellular aromatic proteins and facilitating ABGs construction. The ABGs system achieved over 99 % pyridine removal efficiency and 82 % settleability. Moreover, the proportions of β-sheet and α-helix structures in the extracellular aromatic proteins of ABGs increased, while the random coil structures decreased. This shift in protein structure lowered the surface free energy and energy barriers, which in turn enhanced the surface hydrophobicity and promoted cell adhesion. Furthermore, based on metatranscriptomic analysis, the mechanism for AHL-regulated physiological and behavioral responses between algae and bacteria in ABGs was proposed. This study provides an economically feasible approach to develop efficient and sustainable ABGs systems for industrial wastewater treatment.

Enhanced methane production through synergistic integration of quorum sensing Signals and microbial electrolysis in anaerobic digestion of low-quality biomass

This study explored the synergistic effects of exogenous acyl homoserine lactones (AHLs) and microbial electrolysis (ME) on enhancing anaerobic digestion (AD) of low-quality biomass. The combined AHLs + ME strategy achieved a 79.50 % increase in cumulative methane production compared to the control, outperforming individual treatments. This enhancement was attributed to accelerated substrate degradation, selective enrichment of hydrogenotrophic methanogens (Methanobrevibacter, Methanobacterium, Methanofollis), and strengthened quorum sensing, electron transfer, and methane synthesis pathways. Metagenomic analysis revealed abundance upregulation of key genes involved in AHL synthesis (bjaI, rpaI, braI, rhiI) and sensing (solR, cepR, tofR), direct interspecies electron transfer (pilA, mtrC), and hydrogenotrophic methanogenesis (ftr, mvhD, vhuD, vhcD). This study offers a novel and sustainable strategy to optimize methane production from recalcitrant biomass, advancing AD-based waste-to-energy systems.

Deciphering the internal mechanism of nitrogen removal from sludge and biofilm under low temperature from the perspective of microbial function metabolism

Nitrogen emissions up to the standard are a major challenge for wastewater treatment plants in alpine and high-altitude areas. The dosing of carriers can improve the nitrogen removal efficiency of the system at low temperatures; however, the mechanism of action of sludge and biofilm in nitrogen removal remains unclear. This study elucidated the internal mechanism of nitrogen removal via the function of microbial metabolism in sludge and biofilm at low temperatures. At low temperatures, the biofilm facilitated the enrichment of nitrifying bacteria (5.21%-6.62%) and nitrifying functional genes (amoABC); the average removal efficiency of NH4+-N peaked at 94.14%. The denitrification performance of biofilm (14.34-20.67 mg N/(gMLVSS·h) was weaker than that of sludge (27-30.95 mg N/(gMLVSS·h) at low temperatures. The relative abundance of chemical oxygen demand-degrading, denitrifying bacteria, and denitrification functional genes (napAB, nirS, norB, and nosZ) in the sludge was higher than in the biofilm. With a decrease in temperature, the upregulation of carbon metabolism and quorum-sensing functional genes improved the adaptability of sludge to low temperatures. The enhancement of c-type cytochromes and cyclic dimeric guanosine monophosphate functional genes promoted nitrogen removal by endorsing extracellular electron transfer between microorganisms and releasing extracellular polymeric substances at low temperatures. This study offers new insights into improving the mechanism of nitrogen removal from sludge and biofilm at low temperatures.

Harnessing Microbial Signal Transduction Systems in Natural and Synthetic Consortia for Biotechnological Applications

Signal transduction is crucial for communication and cellular response in microbial communities. Consortia rely on it for effective communication, responding to changing environmental conditions, establishing community structures, and performing collective behaviors. Microbial signal transduction can be through quorum sensing (QS), two-component signal transduction systems, biofilm formation, nutrient sensing, chemotaxis, horizontal gene transfer stress response, and so forth. The consortium uses small signaling molecules in QS to regulate gene expression and coordinate intercellular communication and behaviors. Biofilm formation allows cells to adhere and aggregate, promoting species interactions and environmental stress resistance. Chemotaxis enables directional movement toward or away from chemical gradients, promoting efficient resource utilization and community organization within the consortium. In recent years, synthetic microbial consortia have gained attention for their potential applications in biotechnology and bioremediation. Understanding signal transduction in natural and synthetic microbial consortia is important for gaining insights into community dynamics, evolution, and ecological function. It can provide strategies for biotechnological innovation for enhancing biosensors, biodegradation, bioenergy efficiency, and waste reduction. This review provides compelling insight that will advance our understanding of microbial signal transduction dynamics and its role in orchestrating microbial interactions, which facilitate coordination, cooperation, gene expression, resource allocation, and trigger specific responses that determine community success.

Removal of organic matter from food wastewater using anaerobic digestion at low temperatures enhanced by exogenous signaling molecule N-hexanoyl-homoserine lactone enhancement: Insight to extracellular polymeric substances and key functional genes

This experiment aimed to study the effects of adding the exogenous signaling molecule N-hexanoyl-homoserine lactone (C6-HSL) on the anaerobic digestion of food wastewater at low temperature (15 °C). Daily addition of 0.4 μmol C6-HSL increased the average chemical oxygen demand removal from 45.98% to 94.92%, while intermittent addition (adding 2 μmol C6-HSL every five days) increased it from 45.98% to 72.44%. These two modes of C6-HSL addition increased protease and acetate kinase activity by 47.99%/8.04% and 123.26%/127.91% respectively, and increased coenzyme F420 concentrations by 15.79% and 63.16%, respectively. The regulation of loosely bound extracellular polymeric substances synthesis was influenced by C6-HSL, which increased protein and polysaccharide content in sludge. The relative abundance of Firmicutes and Bacteroidetes increased following addition of C6-HSL. After continuous addition of C6-HSL, the relative abundance of related functional genes such as amy, apgM, aceE, and accC increased, indicating that methanogens obtained sufficient substrate. The abundance of glycolysis-related functional genes such as glk, pfk, pgi, tpiA, gap, pgk, gpmA, eno, and pyk increased after the addition of C6-HSL, ensuring the efficient transformation and absorption of organic matter by anaerobic sludge at low temperatures. This study provides new comprehensive insights into the mechanism behind the enhancement of food wastewater anaerobic digestion by C6-HSL at low temperature.

Enhanced AHL-mediated quorum sensing accelerates the start-up of biofilm reactors by elevating the fitness of fast-growing bacteria in sludge and biofilm communities

Quorum sensing (QS)-based manipulations emerge as a promising solution for biofilm reactors to overcome challenges from inefficient biofilm formation and lengthy start-ups. However, the ecological mechanisms underlying how QS regulates microbial behaviors and community assembly remain elusive. Herein, by introducing different levels of N-acyl-homoserine lactones, we manipulated the strength of QS during the start-up of moving bed biofilm reactors and compared the dynamics of bacterial communities. We found that enhanced QS elevated the fitness of fast-growing bacteria with high ribosomal RNA operon (rrn) copy numbers in their genomes in both the sludge and biofilm communities. This led to notably increased extracellular substance production, as evidenced by strong positive correlations between community-level rrn copy numbers and extracellular proteins and polysaccharides (Pearson's r = 0.529-0.830, P < 0.001). Network analyses demonstrated that enhanced QS significantly promoted the ecological interactions among taxa, particularly cooperative interactions. Bacterial taxa with higher network degrees were more strongly correlated with extracellular substances, suggesting their crucial roles as public goods in regulating bacterial interactions and shaping network structures. However, the assembly of more cooperative communities in QS-enhanced reactors came at the cost of decreased network stability and modularity. Null model and dissimilarity-overlap curve analysis revealed that enhanced QS strengthened stochastic processes in community assembly and rendered the universal population dynamics more convergent. Additionally, these shaping effects were consistent for both the sludge and biofilm communities, underpinning the planktonic-to-biofilm transition. This work highlights that QS manipulations efficiently drive community assembly and confer specialized functional traits to communities by recruiting taxa with specific life strategies and regulating interspecific interactions. These ecological insights deepen our understanding of the rules governing microbial societies and provide guidance for managing engineering ecosystems.

An overview of quorum sensing in shaping activated sludge forms: Mechanisms, applications and challenges

Activated sludge method is an effective method for the wastewater treatment and has been widely applied. Activated sludge usually exists in various forms such as activated sludge floc, biofilm and granule. Due to the different character and function for each sludge type, the role and mechanism in the wastewater treatment process are also different, but all were crucial. The quorum sensing (QS) /quorum quenching (QQ) have been demonstrated and proved to regulate the group behavior by secreting signaling molecules among microorganisms and thus affect the manifestation of sludge. However, the complex mechanisms and regulatory strategies of QS/QQ in sludge forms have not been systematically summarized. This review provided an overview on the mechanism of QS/QQ shaping sludge forms from macro to micro (Explore it through signaling molecules, extracellular polymeric substances and microorganisms). In addition, the application and challenges of QS/QQ regulating sludge forms in various wastewater treatment processes including biofilm batch reactor, granule sludge and membrane bioreactor were discussed. Finally, some suggestions for further research and development of effective and economical QS/QQ strategies are put forward.

Decoding the influence of low temperature on biofilm development: The hidden roles of c-di-GMP

Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.

Biofilm formation and antioxidation were responsible for the increased resistance of N. eutropha to chloramination for drinking water treatment

Chloramination is an effective strategy for eliminating pathogens from drinking water and repressing their regrowth in water distribution systems. However, the inevitable release of NH4+ potentially promotes nitrification and associated ammonia-oxidizing bacteria (AOB) contamination. In this study, AOB (Nitrosomona eutropha) were isolated from environmental water and treated with two disinfection stages (chloramine disinfection and chloramine residues) to investigate the occurrence mechanisms of AOB in chloramination. The results showed that N. eutropha had considerable resistance to monochloramine compared to Escherichia coli, whose inactivation rate constant was 19.4-fold lower. The higher resistance was attributed to high levels of extracellular polymer substances (EPS) in AOB, which contribute to AOB surviving disinfection and entering the distribution system. In AOB response to the chloramine residues stage, the respiratory activity of N. eutropha remained at a high level after three days of continuous exposure to high chloramine residue concentrations (0.5-1.5 mg/L). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) suggested that the mechanism of N. eutropha tolerance involved a significantly high expression of the intracellular oxidative stress-regulating (sodB, txrA) and protein-related (NE1545, NE1546) genes. Additionally, this process enhanced EPS secretion and promoted biofilm formation. Adhesion predictions based on the XDLVO theory corroborated the trend of biofilm formation. Overall, the naturally higher resistance contributed to the survival of AOB in primary disinfection; the enhanced antioxidant response of surviving N. eutropha accompanied by biofilm formation was responsible for their increased resistance to the residual chloramines.

In situ assessment of the initial phase of wastewater biofilm formation: Effect of the presence of algae in an aerobic bacterial biofilm system

The initial start-up attachment stage that dominates biofilm formation is an unstable process and is time-consuming. In the present study, Chlorella sp. was introduced into a general aerobic biofilm system to explore whether the addition of algae improved the initial attachment phase of biofilm. Compared with those of the bacterial biofilms, the initial algal-bacterial biofilms were more stable and had a thicker, denser, and rougher surface. Further investigation suggested that the concentration of extracellular polymeric substances (EPSs) in the algal-bacterial biofilm was 31.33 % greater than that in the bacterial biofilm. Additionally, the algal-bacterial flocs had greater free energies of absolute cohesion (ΔGcoh) and adhesion energy (∆Gadh) than did the bacterial flocs. These phenomena contribute to the speediness and stabilization of initial algal-bacterial start-up biofilms. Specifically, algae inoculation increased microbial community diversity and promoted the growth of bacterial members related to biofilm development. In conclusion, both physicochemical interactions and biological processes strongly influence microbial attachment during the initial biofilm formation process and further promote strengthening.

Comprehensive analysis of effects of magnetic nanoparticles on aerobic granulation and microbial community composition: From the perspective of acyl-homoserine lactones mediated communication

As dosing additives benefit for aerobic granular sludge (AGS) cultivation, effects of different concentrations (0, 10, 50 and 100 mg/L) of magnetic nanoparticles (Fe3O4 NPs) on aerobic granulation, contaminant removal and potential microbial community evolution related to acyl-homoserine lactones (AHLs) mediated bacterial communication were investigated with municipal wastewater. Results showed that the required time to achieve granulation ratio > 70 % was reduced by 60, 90 and 30 days in phase II with addition of 10, 50, 100 mg/L Fe3O4 NPs, respectively. 50 mg/L Fe3O4 NPs can improve contaminant removal efficiency. The promotion of relative abundance of AHLs-producing and AHLs-producing/quenching populations and AHLs-related functional genes accompanied with faster granulation. Iron-cycling-related bacteria were closely related with AHLs-related bacteria during AGS formation. Co-occurrence network analyses showed that AHLs-mediated communication may play an important role in coordinating microbial community composition and functional bacteria participating in nitrogen and polyphosphate metabolisms during aerobic granulation process.

Preparation, characterization, and Staphylococcus aureus biofilm elimination effect of baicalein-loaded tyrosine/hyaluronic acid/β-cyclodextrin-grafted chitosan nano-delivery system

Staphylococcus aureus (S. aureus) is an important cause of infections associated with implanted medical devices due to the formation of bacterial biofilm, which can prevent the penetration of drugs, thus posing a serious multi-drug resistance. Methicillin-resistant Staphylococcus aureus (MRSA) is one of them. In order to enhance the biofilm elimination effect of Baicalein (BA), a BA-loaded Tyr/HA/CD-CS nano-delivery system was successfully prepared using β-cyclodextrin grafted with chitosan (CD-CS), Hyaluronic Acid (HA), and D-Tyrosine (D-Tyr). The Tyr/HA/CD-CS-BA-NPs have a uniform particle size distribution with a particle size of 238.1 ± 3.06 nm and a PDI of 0.130 ± 0.02. The NPs showed an obvious inhibitory effect on planktonic bacteria with a MIC of 12.5 μg/mL. In vivo and in vitro tests showed that the NPs could enhance the elimination effect of BA on the MRSA biofilm. The results of Confocal Laser Scanning Microscopy (CLSM), Live & Dead Kit, and colony count experiments illustrated that Tyr/HA/CD-CS-BA-NPs could enhance the permeability of drugs to the biofilm and improve the ability to kill the biofilm bacteria, which may be an important mechanism to enhance the elimination of the MRSA biofilm. These findings will help develop new, effective medicaments for treating bacterial biofilm infections.

Biofilm formation in xenobiotic-degrading microorganisms

The increased presence of xenobiotics affects living organisms and the environment at large on a global scale. Microbial degradation is effective for the removal of xenobiotics from the ecosystem. In natural habitats, biofilms are formed by single or multiple populations attached to biotic/abiotic surfaces and interfaces. The attachment of microbial cells to these surfaces is possible via the matrix of extracellular polymeric substances (EPSs). However, the molecular machinery underlying the development of biofilms differs depending on the microbial species. Biofilms act as biocatalysts and degrade xenobiotic compounds, thereby removing them from the environment. Quorum sensing (QS) helps with biofilm formation and is linked to the development of biofilms in natural contaminated sites. To date, scant information is available about the biofilm-mediated degradation of toxic chemicals from the environment. Therefore, we review novel insights into the impact of microbial biofilms in xenobiotic contamination remediation, the regulation of biofilms in contaminated sites, and the implications for large-scale xenobiotic compound treatment.

Study of the biofilm mechanism of C4-HSL and C6-HSL in the degradation of quinoline

Quinoline is a hard-to-degrade organic compound widely found in coal chemical wastewater, that seriously affects the ecological environment and human health. A number of biochemical methods are already available for quinoline degradation, but the use of microbial community sensing for quinoline degradation has not been studied in depth. Therefore, this paper focuses on the enhanced mechanism of quorum-sensing signaling molecules in the biofilm formation process during quinoline degradation by functional strains of bacteria. In this paper, the effects of the signal molecules C4-HSL and C6-HSL on the adhesion ability, colony diameter, biofilm formation ability and biofilm morphology of functional strains of quinoline degrading bacteria (Ochrobactrum sp., LC-1) were investigated, and the results showed that both signal molecules promoted the biofilm formation process during the degradation of quinoline by exhibiting an efficient biofortification effect. Both signal molecules could enhance the colony diameter of strain LC-1, where C4-HSL could enhance the biomass of strain LC-1 and stimulate the secretion of extracellular polysaccharides; and C6-HSL could induce the enhancement of adhesion performance and the secretion of extracellular proteins from strain LC-1; both molecules together enhanced the biofilm formation process of strain LC-1. This study has practical application in the degradation of quinoline in coal chemical wastewater.

Responses of the microbial community and the production of extracellular polymeric substances to sulfamethazine shocks in a novel two-stage biological contact oxidation system

Introduction

The biological contact oxidation reactor is an effective technology for the treatment of antibiotic wastewater, but there has been little research investigating its performance on the sulfamethazine wastewater treatment.

Methods

In this study, a novel two-stage biological contact oxidation reactor was used for the first time to explore the impact of sulfamethazine (SMZ) on the performance, microbial community, extracellular polymeric substances (EPS), and antibiotic-resistant genes (ARGs).

Results

The chemical oxygen demand (COD) and ammonia nitrogen (NH 4 + -N) removal efficiencies kept stable at 86.93% and 83.97% with 0.1-1 mg/L SMZ addition and were inhibited at 3 mg/L SMZ. The presence of SMZ could affect the production and chemical composition of EPS in the biofilm, especially for the pronounced increase in TB-PN yield in response against the threat of SMZ. Metagenomics sequencing demonstrated that SMZ could impact on the microbial community, a high abundance of Candidatus_Promineofilum, unclassified_c__Anaerolineae, and unclassified_c__Betaproteobacteria were positively correlated to SMZ, especially for Candidatus_Promineofilum.

Discussion

Candidatus_Promineofilum not only had the ability of EPS secretion, but also was significantly associated with the primary SMZ resistance genes of sul1 and sul2, which developed resistance against SMZ pressure through the mechanism of targeted gene changes, further provided a useful and easy-implement technology for sulfamethazine wastewater treatment.

Biofilm control strategies in the light of biofilm-forming microorganisms

Biofilm is a complex consortium of microorganisms attached to biotic or abiotic surfaces and live in self-produced or acquired extracellular polymeric substances (EPSs). EPSs are mainly formed by lipids, polysaccharides, proteins, and extracellular DNAs. The adherence to the surface of microbial communities is seen in food, medical, dental, industrial, and environmental fields. Biofilm development in food processing areas challenges food hygiene, and human health. In addition, bacterial attachment and biofilm formation on medical implants inside human tissue can cause multiple critical chronic infections. More than 30 years of international research on the mechanisms of biofilm formation have been underway to address concerns about bacterial biofilm infections. Antibiofilm strategies contain cold atmospheric plasma, nanotechnological, phage-based, antimicrobial peptides, and quorum sensing inhibition. In the last years, the studies on environmentally-friendly techniques such as essential oils and bacteriophages have been intensified to reduce microbial growth. However, the mechanisms of the biofilm matrix formation are still unclear. This review aims to discuss the latest antibiofilm therapeutic strategies against biofilm-forming bacteria.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

Rapid start-up of partial nitrification reactor by exogenous AHLs and Vanillin combined with intermittent aeration

Quorum sensing (QS) and quorum quenching (QQ) are common phenomena in microbial systems and play an important role in the nitrification process. However, rapidly start up partial nitrification regulated by N-acyl-homoserine lactones (AHLs)-mediated QS or QQ has not been reported. Hence, we chose N-butyryl homoserine lactone (C₄-HSL) and N-hexanoyl homoserine lactone (C₆-HSL) as the representative AHLs, and Vanillin as the representative quorum sensing inhibitor (QSI) combined intermittent aeration to investigate their effects on the start-up process of partial nitrification. The start-up speed in the group with C₄-HSL or C₆-HSL addition was 1.42 or 1.26 times faster than that without addition, respectively. Meanwhile, the ammonium removal efficiency with C₄-HSL or C₆-HSL addition was increased by 13.87 % and 17.30 % than that of the control group, respectively. And, partial nitrification could maintain for a certain period without AHLs further addition. The increase of Nitrosomonas abundance and ammonia monooxygenase (AMO) activity, and the decrease of Nitrobacter abundance and nitrite oxidoreductase (NXR) activity were the reasons for the rapid start-up of partial nitrification in the AHLs groups. Vanillin addition reduced AMO and hydroxylamine oxidoreductase (HAO) activity, and increased Nitrobacter abundance and NXR activity, thus these were not conducive to achieving partial nitrification. Denitrifying bacteria (Hydrogenophaga, Thauera and Aquimonas) abundance increased in the Vanillin group. QS-related bacteria and gene abundance were elevated in the AHLs group, and reduced in the Vanillin group. Function prediction demonstrated that AHLs promoted the nitrogen cycle while Vanillin enhanced the carbon cycle. This exploration might provide a new technical insight into the rapid start-up of partial nitrification based on QS control.

Enhanced biological S0 accumulation by using signal molecules during simultaneous desulfurization and denitrification

A high rate of elemental sulfur (S⁰) accumulation from sulfide-containing wastewater has great significance in terms of resource recovery and pollution control. This experimental study used Thiobacillus denitrificans and denitrifying bacteria incorporated with signal molecules (C6 and OHHL) for simultaneous sulfide (S^2-) and nitrate (NO₃^-) removal in synthetic wastewater. Also, the effects on S⁰ accumulation due to changes in organic matter composition and bacteria proportion through signal molecules were analyzed. The 99.0% of S^2- removal and 99.3% of NO₃^- was achieved with 66% of S⁰ accumulation under the active S^2- removal group. The S⁰ accumulation, S^2- and NO₃^- removal mainly occurred in 0-48 h. The S⁰ accumulation in the active S^2- removal group was 2.0-6.3 times higher than the inactive S^2- removal groups. In addition, S⁰/SO₄^2- ratio exhibited that S⁰ conversion almost linearly increased with reaction time under the active S^2- removal group. The proportion of Thiobacillus denitrificans and H⁺ consumption showed a positive correlation with S⁰ accumulation. However, a very high or low ratio of H⁺/S⁰ is not suitable for S⁰ accumulation. The signal molecules greatly increased the concentration of protein-I and protein-II, which resulted in the high proportion of Thiobacillus denitrificans. Therefore, high S⁰ accumulation was achieved as Thiobacillus denitrificans regulated the H⁺ consumption and electron transfer rate and provided suppressed oxygen environment. This technology is cost-effective and commercially applicable for recovering S⁰ from wastewater.

Artificially constructing mixed bacteria system for bioaugmentation of nitrogen removal from saline wastewater at low temperature

To alleviate the inhibition effects of multi-stresses, a multi-bacterial bioaugmentation based on stimulating cell-to-cell interactions was applied to improve the stress potential of salt-tolerant aerobic granular sludge (AGS). Results showed that the consortium formed by a combination of salt-tolerant ammonia-nitrogen utilizing bacteria, salt-tolerant nitrite-nitrogen utilizing bacteria and salt-tolerant nitrate-nitrogen utilizing bacteria with a whole biomass ratio of 1:2:1 achieved maximum nitrogen consumption rate (μNH₄⁺-N, μNO₂^--N and μNO₃^--N of 1.03, 0.57 and 11.62 mgN/L·h, respectively) at 35 gNaCl/L salinity and 15 °C. The flocculent consortium was aggregated by Aspergillus tubingensis mycelium pellet, which was made into a compound bacterial agent (CBA), and the comprehensive nitrogen consumption capability of CBA was further improved to 2.47-4.36-fold of single functional bacteria. 5% CBA (m/m) was introduced into the seafood processing wastewater in batches, in winter (12-16 °C), the removal efficiencies of NH₄⁺-N and total nitrogen increased from 66.89% to 52.77% of native AGS system to 79.02% and 69.97% of nascent bioaugmentation system, respectively. The analysis of key enzyme activities demonstrated that the ammonia monooxygenase and nitrate reductase activities of the bioaugmentation system were increased to 2.73-folds and 1.94-folds those of the native system. Moreover, due to an increase of 6.18 mg/gVSS and 0.11 in the secreted exopolysaccharide and tightly-bound/total extracellular polymeric substances, respectively, bioaugmentation boosted the cell bioflocculation ability by 13.53%, which enhanced the robustness. This work provided a detailed and feasible technical proposal for enhancing the biological treatment performance of saline wastewater in cold regions.

Pluripotency of endogenous AHL-mediated quorum sensing in adaptation and recovery of biological nitrogen removal system under ZnO nanoparticle long-term exposure

The impacts of quorum sensing (QS) on nanoparticle (NP)-stressed biological nitrogen removal (BNR) system have seldom been addressed yet. In this study, the contributions of endogenous N-acyl-homoserine lactone (AHL)-based QS regulation to the BNR system's adaptation to the zinc oxide (ZnO) NP stress and its recovery potential were systematically investigated. Although 1 mg/L ZnO NPs exerted little impact on the BNR system, chronic exposure to 10 mg/L ones depressed the system's BNR performance which irreversibly impaired the nitrification process even when the system entered the recovery period with no NP added anymore. Meanwhile, ZnO NPs exhibited hormesis effects on the production of AHLs and extracellular polymeric substance (EPS), and activities of superoxide dismutase and catalase. During the ZnO NP exposure period, C₄-HSL, C₆-HSL, and C₁₀-HSL were discovered to be positively associated with nitrogen removal efficiency, tightly-bound EPS production, and antioxidase activities. Besides, the shifts of Nitrospira, Dechloromonas, Aeromonas, Acinetobacter, Delftia, and Bosea were expected to determine the AHL's dynamic distribution. During the system's recovery stage, Dechloromonas replaced Candidatus_Competibacter as the dominant denitrification-related genus. Dechloromonas abundance elevated with the increased contents of C₄-HSL in the aqueous and EPS phases and C₁₀-HSL in EPS and sludge phases, and were expected to promote the activities of BNR-related and antioxidant enzymes, and the EPS production to assist in the recovery of the impaired system's BNR performance. The QS-related BNR genera exhibited higher resilience to ZnO NPs than quorum quenching-related ones, indicating their critical role in nitrogen removal in the restored system. This work provided an insight into the potential pluripotency of AHL-based QS regulation on the ZnO NP-stressed BNR system's adaptation and recovery.

Quorum sensing improved the low-temperature performance of biofilters treating gaseous toluene

Biofilters usually have poor VOC removal performance at temperatures lower than 20 °C. In this study, two quorum sensing (QS) enhancement methods, which are addition of exogenous N-acyl-homoserine lactones (AHLs) and inoculation of AHL-producing bacteria, were applied in biofilters treating gaseous toluene at a low temperature of 12 °C. Their effects on biofilter performance and biofilm characteristics were investigated. The results showed that adding exogenous AHLs and AHL-producing bacteria in biofilters raised the average toluene elimination capacity by 39% and 26% respectively, and raised the average mineralization efficiency by 25% and 47% respectively in first 24 days. In addition, the two QS enhancement methods could increase the attached biomass by 48% and 87% respectively and made the biofilm distribute more uniform by increasing its extracellular polymeric substances content and microbial adhesive strength. The two QS enhancement methods resulted in more mesopores in biofilm, lower O/C and (O+N)/C of organic elements in biofilm, and increased the solubility of toluene in liquid phase, which all benefit VOCs mass transfer in biofilters. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating VOCs at a low temperature. This work provides us a new choice to improve industrial-scale biofilters treating VOCs at high latitude regions or in winter.

Bioaugmentation with Acinetobacter sp. TAC-1 to enhance nitrogen removal in swine wastewater by moving bed biofilm reactor inoculated with bacteria

To enhance the performance of moving bed biofilm reactor (MBBR) inoculated with heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria, bioaugmentation with Acinetobacter sp. TAC-1 was firstly employed and then the treatment performance for real swine wastewater was presented in this study. Results indicated that NH₄⁺-N and TN removal rates of bioaugmented reactor were significantly improved from 16.53 mg/L/h and 16.15 mg/L/h to 24.58 mg/L/h and 24.45 mg/L/h, respectively. The efficient removal performance (NH₄⁺-N 95.01%, TN 86.40%) for real swine wastewater was achieved within 24 h. Microbial analysis indicated that the composition of functional bacteria varied with the introduction of Acinetobacter sp. TAC-1, especially the abundance of Acinetobacter, Paracoccus and Rhodococcus related to the nitrogen removal. Furthermore, bioaugmentation with Acinetobacter sp. TAC-1 increased abundance of enzymes and functional genes (nirS, nirK and norZ) corresponding to denitrification that may be responsible for the enhanced nitrogen removal performance.

Acceleration of start-up of moving bed biofilm reactor at low temperature by adding specialized quorum sensing bacteria

This study aims to accelerate biofilm formation and operational performance of moving bed biofilm reactor (MBBR) at 5 ℃ by adding specialized Quorum Sensing bacteria (sphingomonas rubra BH3^T). Results showed that bio augmented MBBR (R_S) achieved a higher chemical oxygen demand and NH₄⁺-N removal rate (93% and 75%), which in accordance with its increased biofilm thickness, higher biofilm activity, and nitrifying bacteria abundance (Nitrospira). The increased biofilm thickness (60.23 %) during the whole operating time, accompanied by more potent adhesion force (61.59 %), was related to increased polysaccharides and proteins in the biofilm. Pyrosequencing analysis indicated that BH3^T contributed to higher species richness and triggered the rapid growth of precursor microorganisms (Nakamurella, Micropruina, and Zoogloea) and the enrichment of multifunctional microorganisms (Pseudomonas, Aeromonas, Arcobacter, Dechloromonas, and Flavobacterium) at low temperatures. This study provides an economical and practical new insight into accelerating start-up of MBBR system at low temperature.

Enhanced wastewater treatment performance by understanding the interaction between algae and bacteria based on quorum sensing

In order to further obtain sustainable wastewater treatment technology, in-depth analysis based on algal-bacterial symbiosis, quorum sensing signal molecules and algal-bacterial relationship will lay the foundation for the synergistic algal-bacterial wastewater treatment process. The methods of enhancing algae and bacteria wastewater treatment technology were systematically explored, including promoting symbiosis, reducing algicidal behavior, eliminating the interference of quorum sensing inhibitor, and developing algae and bacteria granular sludge. These findings can provide guidance for sustainable economic and environmental development, and facilitate carbon emissions reduction by using algae and bacteria synergistic wastewater treatment technology in further attempts. The future work should be carried out in the following four aspects: (1) Screening of dominant microalgae and bacteria; (2) Coordination of stable (emerging) contaminants removal; (3) Utilization of algae to produce fertilizers and feed (additives), and (4) Constructing recombinant algae and bacteria for reducing carbon emissions and obtaining high value-added products.

N-acyl-homoserine lactones in extracellular polymeric substances from sludge for enhanced chloramphenicol-degrading anode biofilm formation in microbial fuel cells

Exploring an efficient acclimation strategy to obtain robust bioanodes is of practical significance for antibiotic wastewater treatment by bioelectrochemical systems (BESs). This study investigated the effects of two acclimation conditions on chloramphenicol (CAP)-degrading anode biofilm formation in microbial fuel cells (MFCs). The one was continuously added the extracellular polymeric substances (EPS) extracted from anaerobic sludge and increasing concentrations of CAP after the first start-up phase, while the other was added the EPS-1 (N-acyl-homoserine lactones, namely AHLs were extracted from the EPS) at the same conditions. The results demonstrated that AHLs in the sludge EPS played a crucial role for enhanced CAP-degrading anode biofilm formation in MFCs. The AHL-regulation could not only maintain stable voltage outputs but also significantly accelerate CAP removal in the EPS MFC. The maximum voltage of 653.83 mV and CAP removal rate of 1.21 ± 0.05 mg/L·h were attained from the EPS MFC at 30 mg/L of CAP, which were 0.84 and 1.57 times higher than those from the EPS-1 MFC, respectively. These improvements were largely caused by the thick and 3D structured biofilm, strong and homogeneous cell viability throughout the biofilm, and high protein/polysaccharide ratio along with more conductive contents in the biofilm EPS. Additionally, AHLs facilitated the formation of a biofilm with rich biodiversity and balanced bacterial proportions, leading to more beneficial mutualism among different functional bacteria. More bi-functional bacteria (for electricity generation and antibiotic resistance/degradation) were specifically enriched by AHLs as well. These findings provide quorum sensing theoretical knowledge and practical instruction for rapid antibiotic-degrading electrode biofilm acclimation in BESs.

An attempt to stimulate aniline degrading bioreactor by exogenous auto-inducer: Decontamination performance, sludge characteristics, and microbial community structure response

To break the contradiction between aniline and nitrogen metabolism in activated sludge reactor by influencing microbial interspecific communication, Auto-inducer C6-HSL and 3-oxo-C8-HSL were selected in this study to interfere with aniline degradation system. The two Auto-inducers enhanced the aniline degradation rate and ammonia removal efficiency of the systems, especially C6-HSL. Meanwhile, the main ammonia removal way was assimilation. Exogenous Auto-inducer effectively stabilized the sludge structure and activity from the destruction of aniline, and promoted EPS secretion. Microbial diversity analysis showed that most of functional microflora of seed sludge gradually deactivated with the operation of the reactor, while Rhodococcus, Leucobacter, g_norank_f_Saprospiraceae proliferated wildly under the action of Auto-inducer. Additionally, the interspecific relationship also demonstrated a different trend. Exogenous Auto-inducer was proved to exert positive effects on aniline degradation system to a certain extent, providing new insights in the field of aniline wastewater bio-degradation.

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.

Insight into the effect of N-acyl-homoserine lactones-mediated quorum sensing on the microbial social behaviors in a UASB with the regulation of alkalinity

N-acyl-homoserine lactones (AHLs)-mediated quorum sensing (QS) has been reported as the inducers of microbial social behaviors in anaerobic digestion (AD) processes. However, it is not well understood that how to intentionally change the secretion of AHLs by conventional engineering control such as the regulation of alkalinity. The present research investigated the effect of endogenous AHLs-mediated QS on the microbial social behaviors in an upflow anaerobic sludge bed (UASB) reactor with the influent alkalinity decreased from 2800 mg/L to 700 mg/L by stages. The results showed that the alkalinity of 1800-2200 mg/L was more favorable for the AD in the UASB, with an excellent specific methanogenic activity (SMA) and better microbial aggregation statuses. The alkalinity out of the favorable alkalinity range would decrease the SMA with the accumulation of VFAs in the reactor. It was found that signal molecule C₄-HSL was always the dominant AHL in the UASB along with the decrease of influent alkalinity, while 3-oxo-C₆-HSL, 3-oxo-C₁₂-HSL and C₁₄-HSL were remarkably improved only within the favorable range of alkalinity. Pearson correlation concluded that the dominant signal molecule C₄-HSL was the specific AHL in enhancing the synthesis of extracellular polysaccharide and the metabolism of acidogens. The co-occurrence network revealed that Mesotoga, Sulfurospirillum and Methanoregula were the key hubs in the microbial interaction network, and the AHLs-mediated QS indirectly facilitated the methanogenic metabolism. The present work provided a revealing insight into the effect of AHLs-mediated QS on the microbial social behaviors in AD process with the regulation of alkalinity.

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

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

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.