Soluble Extracellular Polymeric Substances Research Articles

Effects of hydrodynamic conditions on the composition, spatiotemporal distribution of different extracellular polymeric substances and the architecture of biofilms

Microbial biofilms are common on abiotic and biotic surfaces, especially in rivers, which drive crucial ecosystem processes. The microorganisms of biofilms are surrounded by a self-produced extracellular polymeric substance (EPS). In this study, we investigated the effects of different hydrodynamic conditions on the composition, spatiotemporal distribution of different extracellular polymeric substances, and the architecture of biofilms. Multidisciplinary methods offer complementary insights into complex architecture correlations in biofilms. The biofilms formed in turbulent flow with high shear force were thin but dense. However, the biofilms formed under laminar flow conditions were thick but relatively loose. The thickness and compactness of the biofilms formed in the transitional flow were different from those of the other biofilms. The compact structure of the biofilm helped to resist shear forces to minimize detachment. Under the turbulent flow condition, bacteria, exopolysaccharides, and extracellular proteins permeated through the biofilm, and more extracellular polysaccharides enveloped bacteria and extracellular proteins. However, under the transitional flow condition, the extracellular polysaccharides and proteins were fewer than those under the turbulent flow condition; bacteria and algae were seen more prominently in the upper layer of the biofilm. Under the laminar flow condition, the distribution of extracellular polysaccharides, extracellular proteins, and bacteria was relatively uniform throughout the biofilm. The number of extracellular polysaccharides was greater than that of extracellular proteins. The total number of EPS in the biofilm was the largest under turbulent flow condition, followed by that under transitional flow condition and then under laminar flow condition. This study also observed that soluble EPS (S-EPS) were secreted first, followed by loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS). In particular, the adhesion of LB-EPS and flocculation capability of TB-EPS play some role in regulating biofilm formation. This study would help to perfect the five-stages theory of biofilm formation.

Interactions between tannins allelochemicals and extracellular polymeric substance (EPS) of Microcystis aeruginosa.

The protective mechanism of extracellular polymeric substance (EPS) secreted by a harmful cyanobacteria against tannins allelochemicals was explored in this study. The binding properties of soluble EPS (SEPS) and bound EPS (BEPS) of Microcystis aeruginosa to tannic acid (TA) were investigated via fluorescence spectroscopy. The results suggested that TA interacted with the proteins in SEPS and BEPS mainly with binding constants of 5.26 and 7.93 L/mol, respectively; TA interacted with the humic acids in SEPS and BEPS mainly with binding constants of 5.12 and 5.24 L/mol, respectively. Thermodynamic experiments confirmed that the binding was mainly controlled by the hydrophobic force. Combined with Fourier transform infrared spectroscopy, it was found that the amine, carbonyl, carboxyl, and hydroxyl groups in EPS were the main functional groups contributing to the interaction of TA with EPS. The existence of EPS reduced the toxicity of TA to algal cells, with the 96h inhibition rate of 40mg L-1 TA on algal cells decreasing by 48.95%. The results of this study may improve our understanding of the protective mechanism of cyanobacteria against tannins allelochemicals.

Understanding the effects of sludge characteristics on the biosorption of triclosan

On account of hydrophobic nature, the adsorption process on solids is considered as the major pathway for triclosan (TCS) removal in wastewater treatment plants. In this work, four sludge sources (primary sludge, thickened sludge, dewatered sludge, and anaerobic digested sludge) were collected to evaluate the adsorption performance of TCS. The solid-liquid distribution coefficients of TCS were increased with total solids increasing of primary sludge, thickened sludge, and dewatered sludge, whereas decreased in anaerobic digested sludge. Results further revealed differences in sludge floc sub-structures of TCS adsorption. The residues contained most of adsorbed TCS in all sub-structures, while distinguished in various extracellular polymeric substances (EPS). The major contributor of EPS sub-fractions to TCS adsorption was identified as tightly bound EPS in thickened sludge and soluble EPS in anaerobic digested sludge. Based on the excitation-emission matrix spectra and Fourier infrared spectrum results, the protein-like and humic acid-like substances were closely related to the TCS adsorption, and hydrogen bond, hydrophobic interaction, and electrostatic interaction were considered as the dominant mechanisms. This study comprehensively reveals the effects of sludge sources and sub-structures on TCS adsorption, which improves the understanding of interaction and migration processes between TCS and sludge.

Activation of Peroxydisulfate by Bimetallic Nano Zero-Valent Iron for Waste-Activated Sludge Disintegration

Waste-activated sludge (WAS) disintegration using peroxydisulfate (PDS) has attracted scientific attention over the past few years. Despite several advantages offered by a sulfate radical-advanced oxidation process, there are still too many downsides of this treatment that limit its facile large-scale application. This study investigated whether modifying nano zero-valent iron (nZVI) with a second metal such as Ag and Cu enhanced the disruption of WAS. The disintegration efficiency was assessed using standard techniques, i.e., soluble chemical oxygen demand, Fourier-transform infrared spectroscopy and a scanning electron microscope. The bimetallics were shown to have an improved disintegration efficiency of > 2.5-fold compared with the untreated sample. Furthermore, nZVI/Ag was found to be more efficient than nZVI/Cu for PDS activation, which was validated by the higher ratio (3 and 2.5 for nZVI/Ag and nZVI/Cu, respectively) between the soluble extracellular polymeric substances and the bound extracellular polymeric substances (S-EPS/B-EPS). Similar conclusions were derived from a SEM analysis. The improved disintegration efficiency could be related to the enhanced electron transfer from nZVI to PDS or the intrinsic properties of silver, which was found to be one of the best activators for PDS under homogeneous conditions. We believe that this study deepens the understanding of PDS heterogeneous activation processes.

Bacterial extracellular polymeric substances: Impact on soil microbial community composition and their potential role in heavy metal-contaminated soil

In this study, six different treatments involving extracellular polymeric substances (EPS) from Enterobacter sp. FM-1 (FM-1) (no EPS (control), original bacterial cells (FM-1), FM-1 cells with EPS artificially removed (EPS-free cells, EPS-R), different forms of EPS (soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS)) obtained from FM-1) and three types of soils (non-contaminated soil (NC soil), high-contamination soil (HC soil) and low-contamination soil (LC soil)) were used to investigate the impact of different EPS treatments on soil microbial community composition and their potential role in the remediation of heavy metal (HM)-contaminated soil. The results indicate that the EPS secreted by FM-1 played a vital role in changing soil pH and helped increase soil bio- HMs. In addition, EPS secretion by FM-1 helped increase the soil EPS-polysaccharide and EPS-nucleic acid contents; even in HC soil, where the HM content was relatively high, LB-EPS addition still increased the EPS-polysaccharide and EPS-nucleic acid contents in the soil by 1.18- and 15.54-fold, respectively. FM-1, LB-EPS and TB-EPS addition increased the soil invertase, urease and alkaline phosphatase activities and increased the soil organic matter (SOM), NH4+-N and available phosphorus (AP) contents, which helped regulate soil nutrient reserves. Moreover, the addition of different EPS fractions modified the soil microbial community composition to help microbes adapt to an HM-contaminated environment. In the HC and LC soils, where the HM content was relatively high, the soil bacteria were dominated by Protobacteria, while fungi in the soil were dominated by Ascomycota. Among the soil physicochemical properties, the soil SOM and NH4+-N contents and invertase activity significantly impacted the diversity and community composition of both bacteria and fungi in the soil.

A new integrated single-chamber air-cathode microbial fuel cell - Anaerobic membrane bioreactor system for improving methane production and membrane fouling mitigation

A novel integrated single-chamber air-cathode microbial fuel cell - anaerobic membrane bioreactor (ScMFC-AnMBR) system was designed. It involved an anaerobic membrane bioreactor (AnMBR) and a single-chamber air-cathode microbial fuel cell (ScMFC) being constructed in a common reaction chamber to enhance methane production and reduce membrane fouling in the AnMBR. Results indicated that ScMFC-AnMBR delivered a stable micro-bioelectric field environment with a voltage output of 95 ± 4 mV. Compared with conventional AnMBR (C-AnMBR), methane production using this system increased by 35.89%. Soluble microbial product (SMP) and extracellular polymeric substances (EPS) dropped by 65.3% and 43.1%, respectively. Particularly, the transmembrane pressure (TMP) in the operating cycle was in a slow growth status with the maximum value of only 18.5 kPa. The bioelectric field helped aceticlastic methanogens (Methanosaeta) replace hydrogenotrophic methanogens (Methanobacterium) as the dominant methanogens via electron transfer under a closed-circuit scenario. As syntrophic bacteria of methanogens (Syntrophobacter, Smithella and Syner-01) and exoelectrogens of Desulfovibrio were selected by the bioelectric field and gained a stable foothold, bio-foulant (Megasphaera) was significantly reduced. The complex microbial synergism in ScMFC-AnMBR greatly improved the methanogenic performance, thus effectively alleviated membrane fouling and prolonged the operation cycle of the system. Demonstrated here is the feasibility of practical application.

Decrease the effective temperature of hydrothermal treatment for sewage sludge deep dewatering: Mechanistic of tannic acid aided

The formation of refractory compounds and high nitrogen concentrations in filtrates is the bottleneck of hydrothermal treatment (HT) for sludge deep dewatering. To simultaneously solve these two problems, tannic acid (TA)-aided HT was firstly developed in this study. TA addition improved dewaterability under all investigated HT temperatures by improving the sludge relative hydrophobicity. Moreover, the effective HT temperature was reduced from 180 to 160 ℃. The soluble extracellular polymeric substances (S-EPSs) of the sludge hydrothermally treated at 160 ℃ under the optimal TA dose (0.15 mmol/g total solids) contained 47.27% less total organic nitrogen than the S-EPSs of the raw sludge. This result means that the corresponding filtrate contained lower concentrations of refractory compounds and nitrogen than those under the conventional HT conditions and thus could be more easily treated. Furthermore, the changes in the protein secondary structure and the interaction of TA with high-molecular-weight (HMW) proteins in S-EPSs were found to be highly relevant (p < 0.05) to the improvement of sludge dewaterability. With increasing HT temperature (120–180 ℃), the S-EPS HMW proteins with numerous hydrophilic functional groups (hydroxyl and carboxyl) were hydrolyzed, and their secondary structures unfolded; consequently, more sites were exposed for hydrophobic binding with TA, and the TA–protein interaction was more stable and spontaneous. The precipitation of protein with TA also increased with the HT temperature. Thus, TA-aided HT improves protein precipitation and sludge dewaterability through protein structure destruction and the production of more hydrophobic binding sites for TA. The identification of the influencing mechanisms on SS EPS–TA interaction mode and binding capacity are conducive to the further upgrading of TA-aided HT for engineering applications.

The application of sulfate radical-based advanced oxidation processes in hydrothermal treatment of activated sludge at different stages: A comparative study.

Integrating hydrothermal treatment (HT) and advanced oxidation processes (AOP) was proved to be a promising approach for improving sludge dewaterability. In this study, the EPS valorization under elevated temperature and sulfate radical-based AOP were investigated to clarify the valorization of organic matter in different EPS layers and its effects on the sludge dewaterability. Results indicated that the organic matters in the inner layer of EPS decreased sharply with the elevated temperature, and released into the soluble EPS. Sulfate radical-based AOP significantly accelerated the degradation of organics and microbial cells lysis, especially in the presence of ZVI. The protein with the higher hydrophobicity was detected under the AOP enhanced HT. A better synergistic effect on sludge dewaterability was obtained by integrated the AOP at the initial hydrothermal stage. 3D-EEM and parallel factor analysis indicated that the protein and microbial by-product like substances in tightly bound EPS significantly affected the dewaterability.

Bioreduction performance of Cr(VI) by microbial extracellular polymeric substances (EPS) and the overlooked role of tryptophan

Extracellular polymeric substances (EPS) have exhibited promising advantages in mitigating heavy metal contamination, e.g., single-valent silver (Ag(I)), trivalent gold (Au(III)), and hexavalent chromium (Cr(VI)). However, knowledge of the specific substrate in EPSs that supports Cr(VI) reduction has remained elusive. Here, we isolated a novel Cr(VI)-reducing strain with self-mediating properties in an aquatic environment with various pH values to investigate the mechanisms. After analysis by a batch assay coupled with X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and scanning electron microscopy–energy dispersive spectrometry (SEM–EDS) spectroscopic techniques, it was found that Cr(VI) was reduced by the strain and soluble-EPS (S-EPS), and then, organo-trivalent chromium (organo-Cr(III)) was successfully formed. In addition, compared with other components of the strain, the strain and S-EPS completely removed Cr(VI), and the S-EPS exhibited a positive effect on Cr(VI) reduction with a strong monotonic correlation (R2 = 0.999, p = 9.03 × 10−5), indicating that the reduction is an EPS-dependent process. Specifically, the Cr(VI) reduction efficiency was enhanced to 48.85% and 99.4% after EPS and EPS plus tryptophan were added; their respective efficiencies were 3.94 and 8.02 times higher than that of the control assay in which the reductant was depleted. High-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) analysis showed that the tryptophan concentration concomitantly decreased by 61.54%. These findings highlighted the importance of S-EPS and tryptophan and improved our understanding of EPS for Cr(VI) reduction, which might provide a novel strategy for decontaminating targeted heavy metals in future applications.

The essential role of hydrophobic interaction within extracellular polymeric substances in auto-aggregation of P. stutzeri strain XL-2

To enrich the understanding of bio-aggregates formation, the mechanism of auto-aggregation is one of the concerns in wastewater treatment. The auto-aggregation ability by P. stutzeri strain XL-2 was mainly attributed to the self-secretion of extracellular polymeric substances (EPS). A comprehensive correlation analysis indicates that hydrophobic interaction within EPS played essential roles in auto-aggregation. To give insights into the underlying mechanisms, tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) and soluble EPS (S-EPS) were characterized by colorimetry, hydrophobicity, enzymatic hydrolysis, FT-IR spectroscopy and XPS analysis, showing that proteins in TB-EPS comprised a high proportion of hydrophobic carbon-containing (C-containing) functional groups. Further amino acids analysis revealed that these C-containing functional groups might derive from the hydrophobic R groups of amino acids, which significantly affected the surface hydrophobicity of proteins in TB-EPS and thus promoted the auto-aggregation of strain XL-2. This work provides an in-deep understanding of the auto-aggregation mechanism by strain XL-2, which may enrich the understanding of microbial aggregates formation and lead to further application of strain XL-2 in wastewater treatment processes.

Hydraulic Resistance and Macromolecular Structure of Aerobic and Anaerobic Mixed-Culture Extracellular Polymeric Substances Gel Layers: Opportunities and Challenges

Soluble Extracellular Polymeric Substances (sEPS) are a mixture of microbial soluble polymers produced during aerobic or anaerobic treatment of wastewater. Gel layers mainly consisting of sEPS are usually present in the fouling layers of membrane bioreactors (MBRs) and in the dynamic membranes (DMs) of dynamic membrane bioreactors (DMBRs), and their properties have not been thoroughly investigated over the years. In this study, sEPS fractions recovered from aerobic and anaerobic reactors were analyzed and tested to build-up EPS gel layers on a 0.2 µm pore size polycarbonate carrier. Dead-end filtration experiments showed that anaerobic sEPS layers, which have a low polysaccharide:protein (PS:PN) ratio, had a lower hydraulic resistance than the aerobic sEPS gel layers, which show a high PS:PN ratio. Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM) analyses highlighted that both layers had similar thicknesses and 3D structural organizations. Fluorescent staining of organics and biovolume analysis revealed that for the anaerobic sEPS (low PS:PN), the abundance of proteins appears to destabilize the polysaccharide network increasing the water permeability through the layer. Additionally, the polysaccharides present in the anaerobic sEPS were mainly of the α-linked type, contributing to a more open crosslinked network within the layer, resulting in the low filtration resistance measured. The filtration characteristics observed in this study for the sEPS layers from anaerobic mixed cultures are of interest for possible future application of those layers as dynamic membranes within anaerobic reactors.

Critical evaluation of heat extraction temperature on soluble microbial products (SMP) and extracellular polymeric substances (EPS) quantification in wastewater processes.

While soluble microbial products (SMP) and extracellular polymeric substances (EPS) in wastewater bioprocesses have been widely studied, a lack of standard quantification procedures make it difficult to compare results between studies. This study investigated the effect of temperature on SMP and EPS profiles for biological nutrient removal (BNR) sludges and aerobic membrane bioreactor sludge by adapting the commonly used heat extraction and centrifugation scheme, followed by colorimetric quantification of the carbohydrate and protein fractions using the phenol-sulfuric acid (PS) and the bicinchoninic acid (BCA) methods, respectively. To overcome known inconsistencies in colorimetry, total carbon (TC), total nitrogen (TN), and fluorometry analyses were performed in tandem. SMP samples marginally benefitted from heat extraction, owing to their mostly soluble nature, while EPS profiles were greatly influenced by temperature. 60 °C appears to be a suitable general-purpose extraction temperature near the lysis threshold for the sludges tested. The PS method's misestimation due to lack of specificity was observed and contrasted by TC analyses, while the TN analyses corroborated the BCA assays. Fluorometry proved to be a sensitive and rapid analytical method that provided semi-quantitative information on SMP and EPS constituents, particularly its proteinaceous components, with positive implications for robust wastewater process control.

Degradation and utilization of EPS from excessive activated sludge by interaction of electrogenesis and light stimulation

Sticky and gel-like extracellular polymeric substances (EPS) could provide the protective shielding and prevent the microbial cellrupture and lysis as well as increase the difficulty of excessive activated sludge (EAS) biodegradation. Microbial fuel cells (MFCs) are able to accelerate the degradation of EPS and gain electric energy recovery from wastewater simultaneously. In order to discover the role of light stimulation on MFC performance, four reactors were operated in dark (SD), in LED light (SL), in electrogenesis (ED) and in combination of electrogenesis and light (EL), respectively. EPS characteristic, electrochemical performance and anodic microbial community structures were investigated and compared. The results showed that single light stimulation distinctly improved the total EPS especially polysaccharides content in soluble EPS, and Pseudomonas (31.85% relative abundance) as well as Acinetobacter (10.2% relative abundance) became the dominant genera. Single electrogenesis mainly promoted degradation of negatively charged proteins, which was further proved by the enrichment of typical proteolytic and amino acids fermented bacterial genera like Proteiniphilum and Cloacibacillus. Furthermore, the electrochemical activated Petrimonas and syntrophic Syntrophomonas occupied the dominant position indicating the existence of interspecific electron transfer. Moreover, the predominance of Acinetobacter (44.2% relative abundance) and Escherichia/shigella (7.09% relative abundance) in EL reactor implied the synergetic improvement of electrogenesis and light stimulation. In the interaction effect, light stimulation optimized the electricity generation and proteins degradation of MFC.

Changes of network structure and water distribution in sludge with the stratified extraction of extracellular polymeric substances.

The water in sludge is trapped within the extracellular polymeric substance (EPS) with gelatinous structure, greatly challenging the sludge deep dewatering. In this paper, the effect of the EPS viscoelasticity and the structural characteristics of sludge flocs on water distribution was revealed to provide a highly efficient approach in research on sludge dewatering. After biological, and physical method conditioning, the change of viscoelasticity and sludge network structure before/after EPS extraction was comprehensively explored, together with the sludge dewaterability and water distribution. The results suggested the proportion of capillary water and adsorption water carried in soluble EPS (S-EPS) was 59.17% and 40.83%, and that in tightly bound EPS (TB-EPS) was 54.77% and 45.23%, respectively. By contrast, the capillary water in loosely bound EPS (LB-EPS) accounted for as high as 99.99%. In comparison with raw sludge, adsorption water proportion in TB-EPS and S-EPS was reduced after lysozyme (LZM) or freezing-thaw conditioning, which was ascribed to reduction of EPS viscosity and the weakness of water adsorption capacity. Additionally, the sludge yield stress (τy) value first reduced and then increased with the extraction of EPS. Meanwhile, the consistency coefficient (k) also decreased from 4.23Pa·sn to 0.006Pa·sn and then slightly increased after LZM conditioning. This observation indicated the sludge system became sensitive to shearing, and its network structural strength as well as colloid elasticity first weakened and then slightly strengthened. In addition, after LZM or freezing-thaw conditioning, the sludge particle size significantly increased after TB-EPS extraction, while the sludge particle more easily absorbed water molecules, thereby increasing adsorption water and capillary water within the sludge flocs. This phenomenon also resulted in an increasing trend of capillary suction time (CST) after TB-EPS extraction, indicating the deterioration of sludge filtration performance.

Unravelling temperature-dependent fouling mechanism in a pilot-scale anaerobic membrane bioreactor via statistical modelling

Operational temperature is one of the most vital factors that profoundly affect membrane fouling during anaerobic membrane bioreactor operation. This study uncovered the temperature-dependent fouling mechanism in a pilot-scale anaerobic membrane bioreactor treating real municipal wastewater at ambient temperature seasonally fluctuating from 35 to 5 °C. It showed that compared to time accumulation effect of fouling layer, temperature played a more profound role on influencing membrane fouling. Low temperature caused severe membrane fouling by affecting the release of proteinous soluble microbial products (SMP) and extracellular polymeric substances (EPS) and the abundance of related microbial community structure, like Proteobacteria, Firmicutes, Bacteroidetes and Chloroflexi. The path analysis model established in this study, which was statistically significant at 5% level, revealed that temperature could substantially affect SMP and EPS, especially proteinous SMP (β = −0.94, p < 0.01), and thus indirectly influence total fouling rate, since SMP and EPS had significant influence on total fouling rate (p < 0.05). A temperature-based model (R2 > 0.95) was successfully developed in this study for predicting membrane fouling development over the seasons. The output of these two models varied with the type of membrane module. As calculated from the path coefficients, the influence of temperature on the total fouling rate of polymeric membrane (0.70) was greater than that on the total fouling rate of ceramic membrane (0.56). The regression coefficients of the formula obtained from the temperature-based model using the TMP results of polymeric membrane were around twice as large as those obtained from the model using the TMP results of ceramic membrane. These results suggested that ceramic membrane had better anti-fouling property, probably due to its chemical and thermal stability, hydrophilic surface, and well-organized pore structure, as confirmed by the resistance-in-series analysis and excitation-emission matrix (EEM) analysis of the foulant layer.

In-situ manipulation of gel layer fouling into gel layer membrane formation on porous supports for water treatment

The inaccessibility of clean water is one of the growing issues of this era. Indeed, cost-effective and sustainable methods for recycling wastewater are essential. Although membrane separation is an efficient technology for the recycling and purification of water, membrane fouling is still a major drawback of this technology. This work is aimed to develop a dynamic method to form gel layer membranes (GLMs) by manipulating the irreversible fouling process itself as a problem-solving approach. A microporous polyvinylidene fluoride (PVDF) support is subjected to gel layer formation by applying a supernatant of industrial aerobic sludge (containing soluble extracellular polymeric substances EPS) as a feed. Retention of polysaccharides and calcium during the filtration and the topographical analysis after the filtration show that EPS uniformly formed a gel layer on the PVDF support. No further decline in permeability is observed (i.e. remained around 27–33 L/m 2 hr) when the formed GLM is subjected to fouling under similar conditions. Moreover, the percent flux recovery ratio (FRR) of the GLM is also significant (i.e. 90.1 ± 2.71). The retention ability, hydrophilicity, porosity, and water uptake capability of the formed GLM also increased significantly. The optimal performance and stability of GLMs are observed at room temperature (RT) under neutral pH and sub-critical trance membrane pressures (TMP). Based on these results it is suggested that the in-situ manipulation of gel layer fouling is a viable approach for preparing fouling resistant GLMs with high retention efficiency, potentially applicable to wastewater treatment under normal conditions.

Simultaneously enhanced treatment efficiency of simulated hypersaline azo dye wastewater and membrane antifouling by a novel static magnetic field membrane bioreactor (SMFMBR)

Operation performance and membrane fouling of a novel static magnetic field membrane bioreactor (SMFMBR) for treatment of hypersaline azo dye wastewater was investigated. The results showed that SMFMBRs possessed higher efficiency of dye decolorization, COD removal and detoxification than the control MBR without SMF. The (3#) SMFMBR equipped with 305.0 mT (the highest intensity) SMF displayed the best treatment performance among all the four reactors (named as 0#–3#, equipped with SMFs of 0 mT, 95.0 mT, 206.3 mT and 305.0 mT, respectively). Potentially effective microbes belonging to Rhodanobacter, Saccharibacteria genera incertae sedis, Defluviimonas, Cellulomonas, Cutaneotrichosporon, Candida and Pichia were enriched in three SMFMBRs, in both of suspended sludge and bio-cakes. The relative abundance of Candida and Pichia in suspended sludge of 3# SMFMBR was the highest among all the four reactors, suggesting their successful colonization and potentially persistent effect of bioaugmentation. On the other hand, SMF of higher intensity effectively mitigated membrane fouling. Less production of soluble microbial products (SMP) and extracellular polymeric substances (EPS), lower protein/polysaccharide (PN/PS) ratio in SMP and EPS, looser structure of bio-cakes on membrane surface, as well as lower relative abundance of potential fouling causing microbes (mainly bacteria) in microbial communities were determined in 3# SMFMBR than the other three groups.

Accumulation of proteins in the medium of the various naturally occurring Chlorella and Scenedesmus microalgae containing and not-containing algaenan

Depending on a specific strain, the chlorococcalean microalgae cell walls contain or lack a biopolymer called algaenan, highly resistant to chemical and enzymatic treatment. This study aimed to investigate whether the presence or absence of algaenan affects the ability of the selected strains to accumulate proteins in the growth medium. The study was conducted on 20 green microalgae strains, including 11 strains without algaenan and 9 strains with algaenan in their cell walls. The concentration of the proteins in the medium was estimated after 30 days of algae growth using the tannin micromethod. It was demonstrated that algaenan-lacking microalgae accumulated significantly more proteins in the medium than strains containing this biopolymer. Thus, it can be concluded that the cell wall structure resulting from algaenan presence is responsible for the differences in protein accumulation in the medium. These proteins, which are part of the soluble extracellular polymeric substances, can be beneficial for obtaining active substances or can be a factor hindering the application of algae for industrial purposes due to film or foam formation. Thus, the results obtained in this study may give valuable clues for strain selection regarding specific application.

The effect of Bacillus cereus LV-1 on the crystallization and polymorphs of calcium carbonate.

The study of CaCO3 polymorphism is of great significance for understanding the mechanism of carbonate mineralization induced by bacteria and the genesis of carbonate rock throughout geological history. To investigate the effect of bacteria and shear force on CaCO3 precipitation and polymorphs, biomineralization experiments with Bacillus cereus strain LV-1 were conducted under the standing and shaking conditions. The results show that LV-1 induced the formation of calcite and vaterite under the standing and shaking conditions, respectively. However, the results of mineralization in the media and the CaCl2 solution under both kinetic conditions suggest the shear force does not affect the polymorphs of calcium carbonate in abiotic systems. Further, mineralization experiments with bacterial cells and extracellular polymeric substances (EPS) were performed under the standing conditions. The results reveal that bacterial cells, bound EPS (BEPS), and soluble EPS (SEPS) are favorable to the formation of spherical, imperfect rhombohedral, and perfect rhombohedral minerals, respectively. The increase in the pH value and saturation index (SI) caused by LV-1 metabolism under the shear force played key roles in controlling vaterite precipitation, whereas bacterial cells and EPS do not play roles in promoting vaterite formation. Furthermore, we suggest that vaterite formed if pH > 8.5 and SIACC > 0.8, while calcite formed if pH was between 8.0-9.0 and SIACC < 0.8. Bacterial cells and BEPS are the main factors affecting CaCO3 morphologies in the mineralization process of LV-1. This may provide a deeper insight into the regulation mechanism of the polymorphs and morphologies during bacterially induced carbonate mineralization.

Soluble Extracellular Polymeric Substance of Hbga-Expressing Bacterium Influences the Survival and Persistence of Norovirus on Lettuce

Soluble Extracellular Polymeric Substance of Hbga-Expressing Bacterium Influences the Survival and Persistence of Norovirus on Lettuce