Production Of Extracellular Polymers Research Articles

Differences in Biofilm Formation of Listeria monocytogenes and Their Effects on Virulence and Drug Resistance of Different Strains.

Listeria monocytogenes is recognized as one of the primary pathogens responsible for foodborne illnesses. The ability of L. monocytogenes to form biofilms notably increases its resistance to antibiotics such as ampicillin and tetracycline, making it exceedingly difficult to eradicate. Residual bacteria within the processing environment can contaminate food products, thereby posing a significant risk to public health. In this study, we used crystal violet staining to assess the biofilm-forming capacity of seven L. monocytogenes strains and identified ATCC 19112 as the strain with the most potent biofilm-forming. Subsequent fluorescence microscopy observations revealed that the biofilm-forming capacity was markedly enhanced after two days of culture. Then, we investigated into the factors contributing to biofilm formation and demonstrated that strains with more robust extracellular polymer secretion and self-agglutination capabilities exhibited a more pronounced ability to form biofilms. No significant correlation was found between surface hydrophobicity and biofilm formation capability. In addition, we found that after biofilm formation, the adhesion and invasion of cells were enhanced and drug resistance increased. Therefore, we hypothesized that the formation of biofilm makes L. monocytogenes more virulent and more difficult to remove by antibiotics. Lastly, utilizing RT-PCR, we detected the expression levels of genes associated with biofilm formation, including those involved in quorum sensing (QS), flagellar synthesis, and extracellular polymer production. These genes were significantly upregulated after biofilm formation. These findings underscore the critical relationship between extracellular polymers, self-agglutination abilities, and biofilm formation. In conclusion, the establishment of biofilms not only enhances L. monocytogenes' capacity for cell invasion and adhesion but also significantly increases its resistance to drugs, presenting a substantial threat to food safety.

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

Lead remediation by geological fluorapatite combined with Penicillium Oxalicum and Red yeast

Phosphate solubilizing fungi Penicillium oxalicum (POX) and Red yeast Rhodotorula mucilaginosa (Rho) have been applied in Pb remediation with the combination of fluorapatite (FAp), respectively. The secretion of oxalic acid by POX and the production of extracellular polymers (EPS) by Rho dominate the Pb remediation. In this study, the potential of Pb remediation by the fungal combined system (POX and Rho) with FAp was investigated. After six days of incubation, the combination of POX and Rho showed the highest Pb remove ratio (99.7%) and the lowest TCLP-Pb concentration (2.9 mg/L). The EPS combined with POX also enhanced Pb remediation, which has a 99.3% Pb removal ratio and 5.5 mg/L TCLP-Pb concentration. Meanwhile, Rho and EPS can also stimulate POX to secrete more oxalic acid, which reached 1510.1 and 1450.6 mg/L in six days, respectively. The secreted oxalic acid can promote FAp dissolution and the formation of lead oxalate and pyromorphite. Meanwhile, the EPS produced by Rho can combine with Pb to form EPS-Pb. In the combined system of POX + Rho and POX + EPS, all of the lead oxalate, pyromorphite, and EPS-Pb were observed. Our findings suggest that the combined application of POX and Rho with FAp is an effective approach for enhancing Pb remediation.

Key biological processes and essential genes for Proteus mirabilis biofilm development inhibition by protocatechuic acid

Proteus mirabilis is an opportunistic pathogen linked to human urinary tract infections, and is potentially present as a foodborne pathogen within poultry products, including broiler chickens. This report outlines the inhibitory impacts of protocatechuic acid (PCA) on P. mirabilis isolated from a broiler slaughterhouse in China as well as its biofilm. This investigation encompasses assays related to motility and adhesion, bacterial metabolic activity, extracellular polymer (EPS) production, and scavenging capacity. The findings demonstrated that PCA reduced biofilm formation by 61 %. Transcriptomics findings identified that PCA limited the expression of genes like PstS that promote adhesin formation, rbsA and RcsB that alter bacterial chemotaxis, lipopolysaccharide synthesis genes LpxA and EptB, and cell wall synthesis genes MurF and MrdA, and affects the Regulator of Capsule Synthesis (RCS) two-component modulation system. Weighted gene co-expression network analysis (WGCNA) was conducted to identify the core genes. Furthermore, the binding sites of PCA to cytochrome oxidases cydA and cydB, two subunits of ATP synthase atpI and atpH, and ftsZ, which regulate bacterial division, were predicted via molecular docking. Metabolome analysis determined that PCA critically influenced coenzyme A biosynthesis, nucleotide metabolism, alanine, aspartic acid, and glutamate metabolic pathways of P. mirabilis. Therefore, PCA impacts metabolism within bacteria via various pathways, limiting the levels of extracellular polymer and bacterial viability to hinder biofilm formation. Additionally, we prepared an antibacterial plastic film containing protocatechuic acid using PVA as the monomer and CNC as the reinforcing agent. We examined the mechanical and antibacterial properties of this film. When used to wrap chicken, it reduced the total number of colonies, slowed the deterioration of chicken, and maintained the freshness of chicken. In conclusion, the information outlined in this study complements our comprehension of P. mirabilis inhibition by PCA and provides clues for the reduction of foodborne infections associated with P. mirabilis.

Mining of key genes for cold adaptation from Pseudomonas fragi D12 and analysis of its cold-adaptation mechanism.

The psychrotroph Pseudomonas fragi D12, which grew strongly under low temperatures, was screened from tundra soil collected from the permanent alpine zone on Changbai Mountain. To mine the genes critical for cold tolerance and to investigate the cold-adaptation mechanism, whole-genome sequencing, comparative genomic analysis, and transcriptome analysis were performed with P. fragi. A total of 124 potential cold adaptation genes were identified, including nineteen unique cold-adaptive genes were detected in the genome of P. fragi D12. Three unique genes associated with pili protein were significantly upregulated at different degrees of low temperature, which may be the key to the strong low-temperature adaptability of P. fragi D12. Meanwhile, we were pleasantly surprised to find that Pseudomonas fragi D12 exhibited different cold-adaptation mechanisms under different temperature changes. When the temperature declined from 30°C to 15°C, the response included maintenance of the fluidity of cell membranes, increased production of extracellular polymers, elevation in the content of compatibility solutes, and reduction in the content of reactive oxygen species, thereby providing a stable metabolic environment. When the temperature decreased from 15°C to 4°C, the response mainly included increases in the expression of molecular chaperones and transcription factors, enabling the bacteria to restore normal transcription and translation. The response mechanism of P. fragi D12 to low-temperature exposure is discussed. The results provide new ideas for the cold-adaptation mechanism of cold-tolerant microorganisms.

Cinnamaldehyde reduces Yersinia enterocolitica activity and biofilm formation by altering membrane permeability and signalling

Yersinia enterocolitica is a foodborne pathogen that can infect food not only in its planktonic state but also as a biofilm on contact surfaces, making recurrent infections difficult to control. This article discusses various ways in which cinnamaldehyde can combat Y. enterocolitica. These include its effects on the permeability, integrity, and amino acid structure of cell membranes as well as on intracellular energy metabolism. We also investigated the effects of cinnamaldehyde on the formation of biofilms by Y. enterocolitica, including interference with quorum-sensing pathways, bacterial motility and adhesion, extracellular polymer production, and metabolic activity within the biofilm. Our results demonstrated that the minimum concentration of cinnamaldehyde required to effectively inhibit Y. enterocolitica is 0.625 mg/mL. It causes cell death by damaging the membrane, disrupting oxidative respiratory processes, interfering with cellular homeostasis, and disrupting cell function. Correspondingly, a concentration of 0.078 mg/mL cinnamaldehyde can suppress the production of biofilm and signalling molecules. This research aims to explore the mechanism by which cinnamaldehyde inhibits the activity of Y. enterocolitica and its biofilm, with the goal of providing more insight into whether cinnamaldehyde can be used as a natural, plant-based preservative and anti-biofilm agent.

Hydrogel microbial reactor based on microbially induced calcium precipitation for the removal of calcium, cadmium and nitrate from groundwater

In this study, hydrogel biocarriers filled with chia seeds gum biochar encapsulated with Pseudomonas sp. LYF26 were prepared using polyvinyl alcohol and sodium alginate. Simultaneous removal of NO3−, Ca2+ and Cd2+ from low carbon wastewater was achieved by microbially induced carbonate precipitation and denitrification. In order to investigate the performance of the bioreactor, different conditions of hydraulic retention time, pH, and concentration of Cd2+ were studied, and the optimal operating conditions of the bioreactor were finally determined as HRT of 8 h, pH of 6.5 and initial Cd2+ concentration of 3 mg L−1. The results showed that the optimum removal of NO3−-N, Ca2+ and Cd2+ by the reactor was 100%, 54.02% and 100%, respectively. Three-dimensional excitation-emission matrix (3D-EEM) showed that the microorganisms produced extracellular polymers during the operation of the bioreactor, which promoted the removal of Cd2+. Fourier transform infrared spectroscopy (FTIR) detected the presence of -OH, CO, C-O-C and C-O-H, indicating the production of CaCO3 and extracellular polymers. Scanning electron microscope (SEM) observed that the filler surface had a rough and porous character with a large amount of biodeposits attached to its surface. X-ray diffraction (XRD) indicated that the sediments contained CaCO3, CdCO3 and Ca5(PO4)3OH. High-throughput sequencing showed that Pseudomonas was the dominant bacterium.

Interaction of Silica Nanoparticles with Microalgal Extracellular Polymers

The properties of engineered nanoparticles (NPs) in the marine environment are influenced not only by the high ionic strength of seawater but also by the interaction of NPs with naturally occurring components of seawater, especially natural organic matter. The aim of this study was to investigate the interaction of engineered silica nanoparticles (SiO2 NPs, diameter of 12 nm) with microalgal extracellular polymers (EPS) released by the marine diatom Cylindrotheca closterium. Dissolved organic carbon (DOC) content of the prepared EPS suspension (200 μg mL−1) used throughout the study was 3.44 mg C L−1. The incorporation of individual SiO2 NPs (height range 10–15 nm) and their nanoscale aggregates (height up to 25 nm, length up to 600 nm) into the EPS network was visualized by atomic force microscopy (AFM), whereas their molecular-level interaction was unraveled by the change in the signal of the Si-O group in their FTIR spectra. AFM imaging of C. closterium cells taken directly from the culture spiked with SiO2 NPs (10 μg mL−1) revealed that the latter are bound to the EPS released around the cells, predominantly as single NPs (height range 10–15 nm). Since AFM and dynamic and electrophoretic light scattering results demonstrated that SiO2 NPs dispersed in seawater without EPS showed enhanced aggregation (aggregate diameter of 990 ± 170 nm) and a 2.7-fold lower absolute zeta potential value compared to that measured in ultrapure water, our findings suggest that the presence of EPS biopolymers alters the aggregation affinity of SiO2 NPs in the marine environment. This might be of outmost importance during microalgal blooms when increased EPS production is expected because EPS, by scavenging and stabilizing SiO2 NPs, could prolong the presence of NPs in the water column and pose a threat to marine biota.

Microencapsulated reactor for simultaneous removal of calcium, fluoride and phenol using microbially induced calcium precipitation: Mechanism and functional characterization

Fluoride ions (F-) and phenol in groundwater have become a great hurdle to the pursuit of a healthy drinking water source. This study established a microencapsulated immobilization reactor with Aquabacterium sp. CZ3 for the simultaneous removal of nitrate (NO3--N), calcium (Ca2+), F-, and phenol from groundwater with 100%, 67.84%, 88.67%, and 100% removal efficiencies, respectively. The three-dimensional mesh structure of microcapsules facilitated the transport and metabolism of substances, while their synergistic effect with bacteria promoted the removal of contaminants. F- was removed by co-precipitation to generate Ca5(PO4)3F and CaF2 and adsorption. On one hand, the phenol toxicity promoted the production of extracellular polymers and improved the tolerance of bacteria; on the other hand, the degradation of phenol provided a carbon source for bacteria and promoted the denitrification. The development of microencapsulated immobilized reactor provided a clear mechanism for phenol and F- removal under the microbially induced calcium precipitation (MICP) technique, while providing a valuable solution for the treatment of complex groundwater resources.

Degradation of tetracycline wastewater by suspended biochar as carriers in moving bed biofilm reactor.

To improve the removal efficiency of antibiotics in moving bed biofilm reactor, suspended biochar block was prepared by the one-pot process and was used as carriers to construct a reaction device to study the treatment effect of antibiotic wastewater. The characteristics of the hanging biofilm in wastewater were investigated. And the mechanism of biochar as a biological carrier has been studied. The results showed that in the 45-day experiment, the maximum number of biofilms for suspended biochar carriers was twice 3.4 times that of the high-density polyethylene carriers. When 10 mg/L tetracycline was added to the reactor, the removal efficiency of the tetracycline removal rate was 71.85% and the chemical oxygen demand (COD), total nitrogen (TN), and NH4+-N removal efficiency reached to 89.95, 61.91 and 85.47% respectively. Suspension biochar carriers can reduce fluctuations in redox potentials, thereby improving the cellular efficiency of microorganisms. Meanwhile, it inhibits the production of soluble microbial products and extracellular polymers, reduces toxic effects, and enhances the adhesion between microorganisms and carriers. The microbial communities of the two carriers were investigated by high-throughput sequencing techniques. Suspended biochar significantly increased the relative abundance of Hydrogenophaga and Comamonas, and improved the ability of nitrification and denitrification. Comamonas could be responsible for tetracycline degradation.

A comparative study on chemical characterization and properties of surface active compounds from Gram-positive Bacillus and Gram-negative Ochrobactrum strains utilizing pure hydrocarbons and waste mineral lubricating oils.

Mineral lubricating oils are widely used in various industrial sectors for their applications in maintenance and functioning of machineries. However, indiscriminate dumping of these used oils have resulted in polluting the natural reservoirs which subsequently destroys ecological balance. Bacteria can emulsify or lower surface tension between phases of immiscible substrates and can acquire them as their carbon and energy sources. Such a phenomenon is mediated by production of extracellular polymers which can function as eminent surface active compounds based on their surfactant or emulsifying nature. The comparison between bacterial strains (Gram-positive Bacillus stratosphericus A15 and Gram-negative Ochrobactrum pseudintermedium C1) on utilization of pure straight chain hydrocarbons, waste mineral lubricating oils as sole carbon source and chemical characterization of the synthesized surface active compounds were studied. Characterization analysis by Ultraviolet Visible spectrophotometry, Fourier transform infrared spectroscopy, Nuclear Magnetic Resonance spectroscopy, Carbon-Hydrogen-Nitrogen analysis has given detailed structural elucidation of surface active compounds. The contrasting nature of bacterial strains in utilization of different hydrocarbons of waste mineral lubricating oils was observed in Gas Chromatography-Mass Spectroscopy analysis. The variation between both strains in utilization of hydrocarbons can be manifested in chemical structural differences and properties of the produced surface active compounds. Scanning Electron Microscopy has given detailed insight into the microstructural difference of the compounds. The utilization of lubricating oils can address waste disposal problem and offer an economical feasible approach for bacterial production of surface active compounds. Our results suggest that these surface active compounds can maneuver applications in environmental bioremediation and agriculture, pharmaceuticals and food as functional biomaterials.

Effect mechanism of shear stress on hollow anammox granules in low strength wastewater treatment

Hollow anammox granules have been concerned in the field of anammox granular sludge technology. So far, little information is available about the effect of shear stress on hollow anammox granules. The evolution of hollow granular sludge at three shear stresses (τ = 0.014, 0.041, and 0.075 Pa) was investigated in three laboratory scale continuous stirred tank reactors. It was found that the lower shear stress (0.014 Pa) was beneficial to the retention of granules and thus ensured a higher nitrogen removal rate (NRR). A higher shear stress led to a stronger granular sludge abrasion and thus smaller granule size. The results showed that the shear stress affected the production of extracellular polymers (EPS). A higher shear stress resulted in a higher content of EPS. Then, the shear stress had a physical impact on the EPS, which in turn affected the physical and chemical properties of the particles. The increasing shear stress could increase the loose degree of loosely-bound EPS (LB-EPS), and thus facilitated mass transfer, and then enhanced the permeability of anammox granules. On the contrary, the lower shear stress not only weakened the penetration of the substrate, but also hindered the outflow of gas to the outside of the granules. Therefore, the occurrence of cavity changed the internal structure of the anammox granules and affected the distribution of bacteria. In conclusion, this research clarified the impact mechanism of shear stress on the characteristics of hollow anammox granules and provided theoretical guidance for the application in engineering.

Effect of Juglone against Pseudomonas syringae pv Actinidiae Planktonic Growth and Biofilm Formation.

Pseudomonas syringaepv Actinidiae (P. syringae) is a common pathogen causing plant diseases. Limoli proved that its strong pathogenicity is closely related to biofilm state. As a natural bacteriostatic agent with broad-spectrum bactericidal properties, juglone can be used as a substitute for synthetic bacteriostatic agents. To explore the antibacterial mechanism, this study was carried out to examine the inhibitory effect of juglone on cell membrane destruction, abnormal oxidative stress, DNA insertion and biofilm prevention of P. syringae. Results showed that juglone at 20 μg/mL can act against planktogenic P. syringae (107 CFU/mL). Specially, the application of juglone significantly damaged the permeability and integrity of the cell membrane of P. syringae. Additionally, juglone caused abnormal intracellular oxidative stress, and also embedded in genomic DNA, which affected the normal function of the DNA of P. syringae. In addition, environmental scanning electron microscope (ESEM) and other methods showed that juglone effectively restricted the production of extracellular polymers, and then affected the formation of the cell membrane. This study provided a possibility for the development and utilization of natural juglone in plants, especially P. syringae.

Juglone Inactivates Pseudomonas aeruginosa through Cell Membrane Damage, Biofilm Blockage, and Inhibition of Gene Expression

Due to the strong drug resistance of Pseudomonas aeruginosa (P. aeruginosa), the inhibition effects of conventional disinfectants and antibiotics are not obvious. Juglone extracted from discarded walnut husk, as a kind of plant-derived antimicrobial agent, has the advantages of naturalness, high efficiency, and low residue, with a potential role in the inhibition of P. aeruginosa. This study elucidated the inhibitory effect of juglone on the growth of plankton and the formation of P. aeruginosa biofilm. The results showed that juglone (35 μg/mL) had an irreversible inhibitory effect on P. aeruginosa colony formation (about 107 CFU/mL). The integrity and permeability of the cell membrane were effectively destroyed, accompanied by disorder of the membrane permeability, mass leakage of the cytoplasm, and ATP consumption. Further studies manifested that juglone could induce the abnormal accumulation of ROS in cells and block the formation of the cell membrane. In addition, RT-qPCR showed that juglone could effectively block the expression of five virulence genes and two genes involved in the production of extracellular polymers, thereby reducing the toxicity and infection of P. aeruginosa and preventing the production of extracellular polymers. This study can provide support for the innovation of antibacterial technology toward P. aeruginosa in food.

Agent Based Models of Polymicrobial Biofilms and the Microbiome-A Review.

The human microbiome has been a focus of intense study in recent years. Most of the living organisms comprising the microbiome exist in the form of biofilms on mucosal surfaces lining our digestive, respiratory, and genito-urinary tracts. While health-associated microbiota contribute to digestion, provide essential nutrients, and protect us from pathogens, disturbances due to illness or medical interventions contribute to infections, some that can be fatal. Myriad biological processes influence the make-up of the microbiota, for example: growth, division, death, and production of extracellular polymers (EPS), and metabolites. Inter-species interactions include competition, inhibition, and symbiosis. Computational models are becoming widely used to better understand these interactions. Agent-based modeling is a particularly useful computational approach to implement the various complex interactions in microbial communities when appropriately combined with an experimental approach. In these models, each cell is represented as an autonomous agent with its own set of rules, with different rules for each species. In this review, we will discuss innovations in agent-based modeling of biofilms and the microbiota in the past five years from the biological and mathematical perspectives and discuss how agent-based models can be further utilized to enhance our comprehension of the complex world of polymicrobial biofilms and the microbiome.

Coupling iron pretreatment with a constructed wetland-microbial fuel cell to improve wastewater purification and bioelectricity generation

To evaluate the effects of Fe3C pretreatment on constructed wetland-microbial fuel cell performance, iron-free wastewater, ferric iron-containing wastewater, and ferric iron-containing wastewater pretreated with Fe3C were injected into laboratory fuel cells. Wastewater pretreatment can improve sewage treatment, power generation, and microbial growth in microbial fuel cells as ferric iron reacts with Fe3C to generate ferrous iron acting as electron acceptors, accumulating microbial to form cytochrome c, stimulating microbial production of extracellular polymers, reducing internal reactors resistance. Results show that the fuel cells pretreated with Fe3C had the highest removal efficiencies of ammonium nitrogen (96.38 ± 1.87%), total phosphorus (96.52 ± 1.25%) and chemical oxygen demand (74.70 ± 1.67%), and the greatest maximum power density (5.08 mW/m2) and greatest extracellular polymer content. The operational taxonomic units of the electrochemically active bacteria and ferric ammonium oxidizing bacteria Desulfobulbus and Pseudomonas increased significantly (p < 0.05) at the anode of the pretreated fuel cells (342 ± 11 and 98 ± 21) compared with the ferric iron (235 ± 11 and 155 ± 21)) and iron free fuel cells (226 ± 20 and 23 ± 1). This demonstrates that Fe3C pretreatment is environmentally friendly while improving the performance of the device.

Biotechnological potential of soybean molasses for the production of extracellular polymers by diazotrophic bacteria

Abstract In this work, we evaluated the biotechnological potential of soybean molasses - a byproduct from soybean protein concentrate production - as a carbon source for the cultivation of different diazotrophic bacteria in order to produce extracellular polymeric substances (EPS). EPS production was higher with soybean molasses based-medium than mannitol medium for all studied microorganisms, reaching 4.47 g/L (Rhizobium hautlense SEMIA 6450), 4.12 g/L (Ensifer meliloti SEMIA 135) and 3.76 g/L (Mesorhizobium sp. SEMIA 816). The biopolymers were characterized by infrared spectroscopy, showing typical functional groups found in rhizobial polysaccharides. In addition, EPS aqueous-based suspensions (1.0% w/v) showed a shear-thinning flow behavior, suggesting that these biopolymers can present different technological applications. So, the use of this industrial byproduct for the production of biopolymers showed promising results, with possibilities of use in industrial and environmental applications.

The combination of external conditioning and Ca2+ addition prior to the reintroduction of effluent sludge into SBR sharply accelerates the formation of aerobic granules

Aerobic granular sludge (AGS) technology has been limited by its long startup time in sequencing batch reactors (SBRs). The objective of this work is to determine if a new amendment of the AGS process improves sludge granulation rate and pollutants removal efficiency. This amendment consisted in an external conditioning step during which the effluent sludge was dried, supplemented with 0.1 g CaCl2 g−1 dried sludge (DS) and then gradually reintroduced into the SBR. Results have shown that this technique can reduce the granulation time by 17 days while ensuring the stability of AGS. Stable aerobic granules were obtained on day 20, i.e. a few days after reintroducing 1.75 g·L-1 Ca2+-conditioned sludge to the SBR for 5 consecutive days. Mixed liquor suspended solids (MLSS), sludge volume index ratio at 30 min and 5 min (SVI30/SVI5) and average granule size in the AGS reactor were maintained at 5.7 g·L−1, 1.0 and 3.5 mm, respectively. The external conditioning led to an increase in extracellular polymers (EPS) production, a decrease in moisture content, specific oxygen uptake rate (SOUR) and iron precipitation. Altogether, these impacts led to a faster aggregation of the effluent sludge compared to a control SBR. Furthermore, microbial community analyses have shown that the external conditioning process enriched specific Betaproteobacteria (e.g. Thauera genus) in aggregates and AGS. Such outcomes could be linked to the faster granulation rate and more efficient pollutants degradation.

Exploration of the reduction mechanism of Cr(VI) in anaerobic hydrogen fermenter

The bio-reduction of hexavalent chromium (Cr(VI)) by anaerobic fermentation is considered as a promising, low-cost and environment-friendly way. However, it is unclear for the reduction mechanisms of Cr(VI) in an anaerobic hydrogen fermenter, such as reduction kinetics, related electron donors, migration and transformation, reduction site and key components, and related microorganisms. To clarify these issues, a hydrogen fermenter was designed to reduce Cr(VI) at 55 °C with glucose as initial substrate. Results show that 100 mg/L Cr(VI) can be completely reduced (99.5%) to trivalent chromium (Cr(III) through chemical and biological reactions. Bio-reduction dominates Cr(VI) removal in a first-order exponential decay mode with both glucose and its metabolites (volatile fatty acids) as electron donors. Moreover, volatile fatty acids are more suitable as electron donors for Cr(VI) bio-reduction than glucose. Bacilli, Clostridia and Thermotogae in the fermenter dominated the reduction of Cr(VI) by regulating the production and composition of extracellular polymers (EPSs), in which carboxyl and hydroxyl groups play an important role for Cr(VI) reduction by coordination. The results can guide us to regulate the bio-reduction of Cr(VI), and provide reference for the development of bio-reduction technology of Cr(VI).

Extreme thermophilic condition: An alternative for long-term biohydrogen production from sugarcane vinasse

Boosted by the high temperatures in which vinasse is generated (90 °C–100 °C), this study evaluated the effect of an extreme thermophilic condition (70 °C) on sugarcane vinasse Dark Fermentation (DF) in an Anaerobic Structured Bed Reactor (ASTBR). Four hydraulic retention times (HRT) (19, 15, 12 and 8 h) were evaluated. Higher HRT resulted in a greater H2 production rate (690 mLH2.d−1.L−1), higher yields (1.8 molH2.molGlucose−1) and greater stability. The extreme temperature inhibits microorganisms' extracellular polymer production, thus leading to a disperse growth, preventing excess biomass accumulation, which was previously reported as the main drawback in H2 production at lower temperatures. The ASTBR higher void index is also responsible for lower biomass/solids retention. The H2 production main route was through the lactic/acetic acid pathway, which is highly reliant on the pH of fermentation broth. The main genus involved in H2 production at 70 °C were Clostridium, Pectinatus, Megasphaera and Lactobacillus.