Spectroscopic Study of Extracellular Polymeric Substances fromBacillussubtilis: Aqueous Chemistry and Adsorption Effects

Engineering the cell wall reactive groups of Plant Growth Promoting Rhizobacteria by culture strategy for heavy metal removal

This research delved into the effects of nutrient limitation on the level of sporulation and the cadmium adsorption capacity of the bacterium Bacillus sp. isolated from the rhizosphere of endemic soils in the Region of Valparaiso, Chile. The bacteria were subjected to nitrogen limitation in fed-batch mode and were compared to bacteria grown in batch culture without nutrient limitation. The cultures were carried out in a 3 L bioreactor with an external nitrogen supply of ammonium at a flow of 0.123 L h-1. The specific maximum growth rate was 0.42 h-1 in batch and 0.45 h-1 in the exponential phase of the fed-batch. The analysis of sporulation did not show any significant difference between the biomass coming from the fed-batch and batch cultures. It was found that maximum cadmium adsorption capacity varied with culture strategy. The dry biomass grown without nutrient limitation exhibited a maximum adsorption capacity for cadmium of 65.0 mgCd g-1biomass. Conversely, the limited biomass achieved a lower cadmium adsorption capacity of approximately 36.0 mgCd g-1biomass. FTIR analysis showed that nitrogen limitation induced changes in the composition of the outer cell wall, specifically an increase of deacetlylated polysaccharides, reducing the relative amount of secondary amines and proteins from the peptidoglycan matrix. Amino groups from acetylated polysaccharides and proteins have been associated elsewhere with greater cadmium affinity, which could explain the poor results obtained with the nitrogen-restricted biomass. This study shows that new physiological states displaying different adsorption capabilities were effectively obtained by engineering the cell coverage of the bacteria using varying culture strategies. The fed-batch culture proved to be a valuable tool for studying PGPR strains for biosorption and other applications. Exploring diverse nutrient limitations and other pollutants in this bacterium and other members of the PGPR family offer great opportunities to tailor biosorption strategies based on specific conditions, ultimately contributing to sustainable environmental solutions.

Potential Bioactivities, Chemical Composition, and Conformation Studies of Exopolysaccharide-Derived Aspergillus sp. Strain GAD7

This research identified a marine fungal isolate, Aspergillus sp. strain GAD7, which produces an acidic and sulfated extracellular polysaccharide (EPS) with notable anticoagulant and antioxidant properties. Six fungal strains from the Egyptian Mediterranean Sea were screened for EPS production, with Aspergillus sp. strain GAD7 (EPS-AG7) being the most potent, yielding ~5.19 ± 0.017 g/L. EPS-AG7 was characterized using UV-Vis and FTIR analyses, revealing high carbohydrate (87.5%) and sulfate (24%) contents. HPLC and GC-MS analyses determined that EPS-AG7 is a heterogeneous acidic polysaccharide with an average molecular weight (Mw¯) of ~7.34 × 103 Da, composed of mannose, glucose, arabinose, galacturonic acid, galactose, and lyxose in a molar ratio of 6.6:3.9:1.8:1.3:1.1:1.0, linked through α- and β-glycosidic linkages as confirmed by NMR analysis. EPS-AG7 adopted a triple helix-like conformation, as evidenced by UV-Vis (Congo Red experiment) and circular dichroism (CD) studies. This helical arrangement demonstrated stability under various experimental conditions, including concentration, ionic strength, temperature, and lipid interactions. EPS-AG7 exhibited significant anticoagulant activity, doubling blood coagulation time at a concentration of 3.0 mg/mL, and showed significant antioxidant activity, with scavenging activities reaching up to 85.90% and 58.64% in DPPH and ABTS+ assays at 5.0 mg/mL, and EC50 values of 1.40 mg/mL and 3.80 mg/mL, respectively. These findings highlight the potential of EPS-AG7 for therapeutic applications due to its potent biological activities.

The corncobs-loaded iron nanoparticles enhanced mechanism of denitrification performance in microalgal-bacterial aggregates system when treating low COD/TN wastewater

To improve denitrification efficiency of microalgal-bacterial aggregates (MABAs) when treating low carbon to nitrogen (C/N) ratio wastewater, CK (the biological control), C1 (untreated corncobs), C2 (alkali-treated corncobs), CFe1 (C1 loaded iron nanoparticles) and CFe2 (C2 loaded iron nanoparticles) five groups of experiments were installed under artificial light (1600 lm). After 36 h of experiment, NO3--N was almost completely converted in CFe1 following by CFe2 when the initial concentration was 60.1 mg/L, whose NO3--N conversion rates were 6.2 and 3.4 times faster than the CK group, respectively. The result showed that the corncobs-loaded iron nanoparticles (CFe1, CFe2) had the potential to promote denitrification process and the CFe1 was more effective. Meanwhile, the CFe1 and CFe2 resulted in a decreased content in extracellular polymeric substances (EPS) secretion because iron nanoparticles (Fes) promoted electron transport and alleviated the nitrate stress. Moreover, the electrochemical analysis of EPS showed that the corncobs and corncobs-loaded iron nanoparticles improved the electron transport rate and redox active substances production. The increase in electron transport activity (ETSA), adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH) also indicated that the CFe1 and CFe2 promoted microbial metabolic activity and the electron transport rate in MABAs. In addition, the CFe1 group enhanced the enrichment of Proteobacteria, Patescibacteria, Chlorophyta and Ignavibacteriae, which was contributed to the nitrogen removal performance of MABAs. In summary, the enhancement mechanism of corncobs-loaded iron nanoparticles on denitrification process of MABAs was depicted through EPS secretion, electrochemical characteristics, microbial metabolic activity and microbial community. The article provides a viable program for enhancing the denitrification performance of MABAs when treating low C/N wastewater.

Recovery of Y(III) from wastewater by Pseudomonas psychrotolerans isolated from a mine soil

While microbial technologies, which are considered to be environmentally friendly, have great potential for the recovery of rare earth elements (REEs) from mining wastewater, their applications have been restricted due to a lack of efficient biosorbents. In this study, a strain of Pseudomonas psychrotolerans isolated from yttrium-enriched mine soil was used to recover yttrium (Y(III)) from rare-earth mining wastewater. At an initial Y(III) dose of 50 mg L-1, the amount of Y(III) adsorbed by P. psychrotolerans reached 99.9 % after 24 h. Various characterization techniques revealed that P. psychrotolerans adsorbed Y(III) mainly through complexation of oxygen-containing functional groups and electrostatic interactions. A high level of adsorption efficiency (>99.9 %) was maintained after five consecutive adsorption/desorption cycles, indicating that P. psychrotolerans was highly reusable. While the efficiency of adsorbing Y(III) by P. psychrotolerans decreased (34.4 %) in actual rare earth mining wastewater, selectivity toward other REEs (≤ 18.4 %) was still observed. Consequently, this study provides a promising green, environmentally friendly and sustainable microbial approach for the selective recovery of REEs from rare earth wastewater.

Genome and pan-genome analysis of a new exopolysaccharide-producing bacterium Pyschrobacillus sp. isolated from iron ores deposit and insights into iron uptake

Bacterial exopolysaccharides (EPS) have emerged as one of the key players in the field of heavy metal-contaminated environmental bioremediation. This study aimed to characterize and evaluate the metal biosorption potential of EPS produced by a novel Psychrobacillus strain, NEAU-3TGS, isolated from an iron ore deposit at Tamra iron mine, northern Tunisia. Genomic and pan-genomic analysis of NEAU-3TGS bacterium with nine validated published Psychrobacillus species was also performed. The results showed that the NEAU-3TGS genome (4.48 Mb) had a mean GC content of 36%, 4,243 coding sequences and 14 RNA genes. Phylogenomic analysis and calculation of nucleotide identity (ANI) values (less than 95% for new species with all strains) confirmed that NEAU-3TGS represents a potential new species. Pangenomic analysis revealed that Psychrobacillus genomic diversity represents an "open" pangenome model with 33,091 homologous genes, including 65 core, 3,738 shell, and 29,288 cloud genes. Structural EPS characterization by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy showed uronic acid and α-1,4-glycosidic bonds as dominant components of the EPS. X-ray diffraction (XRD) analysis revealed the presence of chitin, chitosan, and calcite CaCO3 and confirmed the amorphous nature of the EPS. Heavy metal bioabsorption assessment showed that iron and lead were more adsorbed than copper and cadmium. Notably, the optimum activity was observed at 37°C, pH=7 and after 3 h contact of EPS with each metal. Genomic insights on iron acquisition and metabolism in Psychrobacillus sp. NEAU-3TGS suggested that no genes involved in siderophore biosynthesis were found, and only the gene cluster FeuABCD and trilactone hydrolase genes involved in the uptake of siderophores, iron transporter and exporter are present. Molecular modelling and docking of FeuA (protein peptidoglycan siderophore-binding protein) and siderophores ferrienterobactine [Fe+3 (ENT)]-3 and ferribacillibactine [Fe+3 (BB)]-3 ligand revealed that [Fe+3 (ENT)]-3 binds to Phe122, Lys127, Ile100, Gln314, Arg215, Arg217, and Gln252. Almost the same for [Fe+3 (ENT)]-3 in addition to Cys222 and Tyr229, but not Ile100.To the best of our knowledge, this is the first report on the characterization of EPS and the adsorption of heavy metals by Psychrobacillus species. The heavy metal removal capabilities may be advantageous for using these organisms in metal remediation.

Soil organic carbon sequestration potential explained by mineralogical and microbiological activity using spectral transfer functions

The ability of soil to sequester carbon and reduce atmospheric CO2 concentrations is limited and depends on the soil minerals and their interaction with the microbiota. Microbial activities are closely associated with the types and amounts of soil organic matter (SOM) and clay minerals that have functional groups that interact with energy in Vis NIR-SWIR and Mid-IR wavelengths. The main objective of this research was to determine, based on these spectral ranges, the relation between mineralogical and organic compounds, as their sequestration and specialization in soils from Brazil. It was possible to map microbiological activity by spectral transfer functions and digital soil mapping reaching R2 from 0.77 to 0.85. Multiple regression equations were constructed to quantify enzymatic activity, microbial biomass carbon (MBC), particulate organic matter (POM), and resistant forms of carbon, and SOM associated with the mineral fraction (MAOM). All these properties were detected by specific bands obtained with the recursive feature elimination (RFE) algorithm, reaching correlations from 0.64 to 0.98 in specific ranges. The prediction model of the carbon sequestration potential was adjusted with microbiological and mineralogical variables from Vis-NIR-SWIR and the Mid-IR spectral range. A SARAR double autoregressive model was adjusted with r 0.61 and to a spatial error model (SEM) with r 0.7. The explanatory variables were associated with kaolinite, hematite, goethite, gibbsite, and the abundance of fungi, actinomycetes, vesico-arbuscular mycorrhizal fungi, enzymatic activity of beta-glucosidase, urease and phosphatase, and POM. Among the microbiological variables, the general abundance of fungi was the most important, in contrast to enzymatic activity that was the least important. The interaction between the different maps constructed and historical land use allowed the identification of areas that contribute to sequestering new carbon and could be the key to climate change mitigation strategies.

Multimodal characterization of the collagen hydrogel structure and properties in response to physiologically relevant pH fluctuations

pH fluctuations within the extracellular matrix (ECM) and its principal constituent collagen, particularly in solid tumors and chronic wounds, may influence its structure and function. Whereas previous research examined the impact of pH on collagen fibrillogenesis, this study focuses on determining how pH fluctuations affect collagen hydrogels that mimic the physiological ECM. Utilizing a type I collagen hydrogel, we examined the influence of pH fluctuations on its structure, properties, and function while keeping the collagen hydrated. We show that collagen's secondary structure remains unaltered during pathologically relevant microenvironmental pH changes. By employing cryo scanning electron microscopy and artificial intelligence-assisted image analysis, we show that at physiological pH, collagen hydrogel presents densely packed, aligned, and elongated fibrils, which upon a decrease to pH 6.5, are transformed into shorter, sparser, and disoriented fibrils. The collagen possesses a higher storage modulus yet a lower permeability at pH 7 and 7.8 compared with pH 6.5 and 7.4. Exposing acidified collagen to a basic buffer reinstates its native structure and viscoelastic properties. Our study offers an innovative approach to analyze and characterize perturbations in hydrated collagen-based systems with potential implications for better understanding and combating disease progression. STATEMENT OF SIGNIFICANCE: As the main component of the extracellular matrix, collagen undergoes conformational changes associated with pH changes during disease. We analyze the impact of pH on pre-formed collagen fibers mimicking healthy tissues subjected to disease, and do not focus on the more studied fibrillogenesis process. Using cryogenic SEM, which allowed imaging close to the native state, we show that even minor fluctuations in the pH affect the collagen thickness, length, fiber alignment, and rheological properties. Following exposure to acidic pH, the collagen had short fibers, lacked orientation, and had low mechanical strength. This acidic collagen restored its original properties after returning to a neutral pH. These findings can help determine how pH changes can be modulated to restore healthy collagen properties.

Characterization of an antimony-resistant fungus Sarocladium kiliense ZJ-1 and its potential as an antimony bio-remediator

Antimony (Sb) is a toxic metalloid widely distributed in the natural environments. Microorganisms, especially fungi, could serve as ideal biomaterials for bioremediation of Sb-polluted soils and waters. In this study, we isolated an antimony-resistant fungus, Sarocladium kiliense ZJ-1, from a slag sample collected in Xikuangshan Sb mine in P. R. China. ZJ-1 showed an extremely high resistance to Sb, with a MIC level of > 175 mM for arsenite [Sb(Ⅲ)] and 40 mM for arsenate [Sb(V)]. Whole genomic analysis identified multiple Sb (Ⅲ)- and/or As(Ⅲ)-resistant genes on ZJ-1's genome, which may partially explain its hyper-resistance to Sb. The potential of ZJ-1 in removing Sb from Sb(Ⅲ) or Sb(V) solutions was also quantified. The average biosorption capacity of ZJ-1 for Sb(Ⅲ) and Sb(V) is 635.14 mg/g and 149.65 mg/g, respectively, in Sb aqueous solutions with an initial concentration of 2000 mg/L (16.43 mM). Besides, almost 99% of Sb(Ⅲ) in the growing system was removed with an initial concentration of 500 mg/L (4.11 mM). Furthermore, Fourier transformation infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were used to probe the Sb adsorption mechanism on ZJ-1, and -OH, -NH2, -COOH, C-O and C-O-C were found to be the main surface functional groups of ZJ-1 cells to adsorb Sb.

The effects of didodecyl dimethyl ammonium chloride on microbial communities and resistance genes in floc, granular and biofilm denitrification sludge

As a type of quaternary ammonium compounds, didodecyl dimethyl ammonium chloride (DADMAC C12) was frequently detected in wastewater treatment plants. Here, floc-based sequencing batch reactor (FSBR), granule-based SBR (GSBR) and biofilm SBR (BSBR) were fed with 0.5, 5 and 10 mg/L of DADMAC C12 for 120 d. Compared with floc sludge and granule sludge, biofilm had the strongest ability to resist the impact of DADMAC C12. Notably, in both FSBR and GSBR systems, 5 mg/L DADMAC C12 promoted denitrification sludge to become hydrophobic and compact due to an increase in α-Helix/(β-Sheet+Random coil), consequently enhancing sludge granulation. Besides，high concentration of DADMAC C12 generally increased the abundances of MGEs in three denitrification systems, except extracellular MGEs in water. The variation of efflux pump ARGs was basically consistent with that of MGEs. The stimulation of DADMAC C12 also increased significantly the abundance of extracellular antibiotics deactivation ARGs in water in three denitrification systems. Besides, DADMAC C12 induced co-selection among various ARGs and promoted the proliferation and spread of sulfonamide ARGs in water.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Growth of the Nitrosomonas europaea cells in the biofilm and planktonic growth mode: Responses of extracellular polymeric substances production and transcriptome

Nitrosomonas europaea, an aerobic ammonia oxidizing bacterium, is responsible for the first and rate-limiting step of the nitrification process, and their ammonia oxidation activities are critical for the biogeochemical cycling and the biological nitrogen removal of wastewater treatment. In the present study, N. europaea cells were cultivated in the inorganic or organic media (the NBRC829 and the nutrient-rich, NR, media, respectively), and the cells proliferated in the form of planktonic and biofilm in those media, respectively. The N. europaea cells in the biofilm growth mode produced larger amounts of the extracellular polymeric substances (EPS), and the composition of the EPS was characterized by the chemical analyses including Fourier transform infrared spectroscopy (FT-IR) and 1H-nuclear magnetic resonance (NMR) measurements. The RNA-Seq analysis of N. europaea in the biofilm or planktonic growth mode revealed that the following gene transcripts involved in central nitrogen metabolisms were abundant in the biofilm growth mode; amo encoding ammonia monooxygenase, hao encoding hydroxylamine dehydrogenase, the gene encoding nitrosocyanine, nirK encoding copper-containing nitrite reductase. Additionally, the transcripts of the pepA and wza involved in the bacterial floc formation and the translocation of EPS, respectively, were also abundant in the biofilm-growth mode. Our study was first to characterize the EPS production and transcriptome of N. europaea in the biofilm and planktonic growth mode.

Reconceptualization of the mechanism of thermal hydrolysis pretreatment to enhance the anaerobic conversion of sludge organic nitrogen: Decisive role of organic nitrogen occurrence

The occurrence state of organic nitrogen (ON) is the key to affect anaerobic biotransformation of sludge. ON in sludge was chemically classified as PA (easily accessible part), PB (moderately accessible) and PC (hardly accessible) according to the modified CNCPS method. The components of them were analyzed by PY-GCMS, and it was identified that PA was extracellular amino acids, peptides and proteins; PB was genetic material, cell wall peptidoglycans and intracellular proteins; PC was ON that cross-linked with complex macromolecules. The conversion characteristics of PA, PB and PC in sludge and their relationship with anaerobic digestion (AD) performance were investigated after thermal hydrolysis pretreatment (THP) at different temperatures (100-180 °C). With the increase of THP temperature, the hydrolysis of PA and the conversion of PB to PA were promoted. At 180-THP, part of PA was converted to PC due to thermochemical reactions. In the fast degradation stage of AD of ON (ON-fast), PA is the main component of degradation; while in the slow degradation stage (ON-slow), the degradation of ON is mainly dominated by PB. Therefore, THP can significantly increase the proportion of ON-fast and reduce the ON fraction in the digestate (ON-hard). Moreover, PA and PB, rather than PC, were identified as dominant in ON-hard with or without THP for the first time, overturning the traditional view (remaining ON after AD was that cross-linked with complex macromolecules). This is due to that PA and PB are the main ON that make up microbial cells. The findings upgraded our perspective on conversion of ON of sludge during AD and inspire the shifted focus from "degrading PC" to "PC accumulation" for later use, through targeted enhanced PA degradation.

Construction of synthetic anti-fouling consortia: fouling control effects and polysaccharide degradation mechanisms

The physical states and chemical components of bulk sludge determine the occurrence and development of membrane fouling in membrane bioreactors. Thus, regulation of sludge suspensions can provide new strategies for fouling control. In this study, we used "top-down" enrichment to construct a synthetic anti-fouling consortium (SAC) from bio-cake and evaluate its roles in preventing membrane fouling. The SAC was identified as Massilia-dominated and could almost wholly degrade the alginate solution (1,000 mg/L) within 72 h. Two-dimensional Fourier transformation infrared correlation spectroscopy (2D-FTIR-CoS) analysis demonstrated that the SAC induced the breakage of glycosidic bond in alginates. The co-cultivation of sludge with a low dosage of SAC (ranging from 0 to 1%) led to significant fouling mitigation, increased sludge floc size, and decreased unified membrane fouling index value (0.55 ± 0.06 and 0.11 ± 0.05). FTIR spectra and X-ray spectroscopy analyses demonstrated that the addition of SAC decreased the abundance of the O-acetylation of polysaccharides in extracellular polymeric substances. Secondary derivatives analysis of amide I spectra suggested a strong reduction in the α-helix/(β-sheet + random coil) ratio in the presence of SAC, which was expected to enhance cell aggregation. Additionally, the extracellular secretions of SAC could both inhibit biofilm formation and strongly disperse the existing biofilm strongly during the biofilm incubation tests. In summary, this study illustrates the feasibility and benefits of using SAC for fouling control and provides a new strategy for fouling control.

Thermal Effect on Algae, Biofilm and Their Composition Towards Membrane Distillation Unit: A Mini-review

Membrane distillation (MD) has lower operating temperature and potential to recycle waste heat for desalination which catches much attention of the researchers in the recent years. However, the biofouling is still a challenging hurdle to be overcome for such applications. The microbial growth rate, secretion and biofilm formation are sensitive to heat. Membrane distillation is a thermally driven separation, so the increase of temperature in the seawater feed could influence the extent of biofouling on the unit parts. In this review, we present the effect of temperature on algal growth, the range of temperature the microbes, marine algae and planktons able to survive and the changes to those planktons once exceed the critical temperature. Thermal effect on the biofilm, its composition and properties are discussed as well, with association of the biofilm secreting microbes, but the study related to membrane distillation unit seems to be lacking and MD biofouling factors are not fully understood. Characterization of the algae, biofilm and EPS that govern biofouling are discussed. This information not only will help in designing future studies to fill up the knowledge gaps in biofouling of membrane distillation, but also to some extent, assist in pointing out possible fouling factors and predicting the degree of biofouling in the membrane distillation unit.

Extracellular polymeric substances and mineral interfacial reactions control the simultaneous immobilization and reduction of arsenic (As(V))

Extracellular polymeric substances (EPS) play a crucial role in controlling the mobility and bioavailability of heavy metal(loid)s in water, soils, and sediments. The formation of EPS-mineral complex changes the reactivity of the end-member materials. However, little is known about the adsorption and redox mechanisms of arsenate (As(V)) in EPS and EPS-mineral complexes. Here we examined the reaction sites, valence state, thermodynamic parameters and distribution of As in the complexes using potentiometric titration, isothermal titration calorimetry (ITC), FTIR, XPS, and SEM-EDS. The results showed that ∼54% of As(V) was reduced to As(III) by EPS, potentially driven by an enthalpy change (ΔH) of - 24.95 kJ/mol. The EPS coating on minerals clearly affected the reactivity to As(V). The strong masking of functional sites between EPS and goethite inhibited both the adsorption and reduction of As. In contrast, the weak binding of EPS onto montmorillonite retained more reactive sites for the reaction with As. Meanwhile, montmorillonite facilitated the immobilization of As to EPS through the formation of As-organic bounds. Our findings deepen the understanding of EPS-mineral interfacial reactions in controlling the redox and mobility of As, and the knowledge is important for predicting the behavior of As in natural environments.

Stability of organic matter-iron-phosphate associations during abiotic reduction of iron

The stability of organic matter-iron-phosphate (OM-Fe-P) association has an important impact on the migration and sequestration of organic carbon (OC) and P in the environment. Here, we examined the release characteristics of Fe, P and OM due to the abiotic reduction of OM-Fe-P associations by Na-dithionite. The associations were synthesized with algae-derived OM (AOM) and terrestrial humic acid (HA) through either adsorption onto iron (hydr)oxide or coprecipitation with Fe(III). Results indicated that OM and P adsorbed onto the associations were rapidly released, whereas coprecipitation yielded much lower release rates of Fe, P, and OM. The stronger inhibitory effect on reduction from coprecipitation can be explained by larger particles formed by coprecipitation and coprecipitation taking up more OC that had a passivation effect on the associations. The release rates of OM and P were lower in coprecipitates formed with HA than formed with AOM for a given OC/Fe ratio. This observation can be attributed to a patchy distribution of OC in AOM associated coprecipitates, which showed a weaker aggregation of OC with Fe and P. In contrast, the distribution of OC in HA-associated coprecipitates was more homogenous, enabling a stronger aggregation of OM with P and a greater passivation effect on P release. Our results revealed that OM sources, association formation pathways, and elemental stoichiometry collectively controlled the stability of OM-Fe-P associations.

Decoding the Role of Extracellular Polymeric Substances in Enhancing Nitrogen Removal from High-Ammonia and Low-C/N Wastewater in a Sequencing Batch Packed-Bed Biofilm Reactor

Although the role of extracellular polymeric substances (EPSs) as a viscous high-molecular polymer in biological wastewater treatment has been recognized, in-depth knowledge of how EPSs affect nitrogen removal remains limited in biofilm-based reactors. Herein, we explored EPS characteristics associated with nitrogen removal from high-ammonia (NH₄⁺-N: 300 mg/L) and low carbon-to-nitrogen ratio (C/N: 2-3) wastewater in a sequencing batch packed-bed biofilm reactor (SBPBBR) under four different operating scenarios for a total of 112 cycles. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared (FTIR) analysis revealed that the distinct physicochemical properties, interface microstructure, and chemical composition of the bio-carrier were conducive to biofilm formation and microbial immobilization and enrichment. Under the optimal conditions (C/N: 3, dissolved oxygen: 1.3 mg/L, and cycle time: 12 h), 88.9% ammonia removal efficiency (ARE) and 81.9% nitrogen removal efficiency (NRE) could be achieved in the SBPBBR. Based on visual and SEM observations of the bio-carriers, biofilm development, biomass concentration, and microbial morphology were closely linked with nitrogen removal performance. Moreover, FTIR and three-dimensional excitation-emission matrix (3D-EEM) spectroscopy demonstrated that tightly bound EPSs (TB-EPSs) play a more important role in maintaining the stability of the biofilm. Significant shifts in the number, intensity, and position of fluorescence peaks of EPSs determined different nitrogen removal. More importantly, the high presence of tryptophan proteins and humic acids might promote advanced nitrogen removal. These findings uncover intrinsic correlations between EPSs and nitrogen removal for better controlling and optimizing biofilm reactors.

Quaternary ammonium compounds promoted anoxic sludge granulation and altered propagation risk of intracellular and extracellular antibiotic resistance genes

Surfactants could influence sludge morphology and disinfectants were linked to antibiotic resistance genes (ARGs). Thus, the response of activated sludge and ARGs to long-term quaternary ammonium compounds (QACs) exposure required further investigation, which is a popular surfactant and disinfectant. Here, three sequencing batch reactors were fed with 5 mg/L most frequently detected QACs (dodecyl trimethyl ammonium chloride (ATMAC C12), dodecyl benzyl dimethyl ammonium chloride (BAC C12) and didodecyl dimethyl ammonium chloride (DADMAC C12)) for 180 d. The long-term inhibitory effect on denitrification ranked: DADMAC C12 > BAC C12 > ATMAC C12. Besides, obvious granular sludge promoted by the increase of α-Helix/(β-Sheet + Random coil) appeared in DADMAC C12 system. Moreover, intracellular ARGs increased when denitrification systems encountered QACs acutely but decreased in systems chronically exposed to QACs. Although replication and repair metabolism in ATMAC C12 system was higher, ATMAC C12 significantly promoted proliferation of extracellular ARGs. It was noteworthy that the propagation risk of extracellular ARGs in sludge increased significantly during sludge granulation process, and intracellular sul2 genes in sludge and water both increased with the granular diameter in DADMAC C12 system. The universal utilization of QACs may enhance antibiotic resistance of bacteria in wastewater treatment plants, deserving more attention.

Formation mechanism of disc-shaped calcite-a case study on Arthrobacter sp. MF-2

Research on the biogenic-specific morphology of carbonate minerals has made progress in the fields of biomineralization and industrial engineering. In this study, mineralization experiments were performed using Arthrobacter sp. MF-2, including its biofilms. The results showed that a particular morphology of minerals (i.e., disc-shaped) was observed in the mineralization experiments with strain MF-2. The disc-shaped minerals were formed near the air/solution interface. We also observed that disc-shaped minerals formed in experiments with the biofilms of strain MF-2. Therefore, the nucleation of carbonate particles on the biofilm templates produced a novel disc-shaped morphology which was assembled from calcite nanocrystals radiating out from the periphery of the template biofilms. Further, we propose a possible formation mechanism of the disc-shaped morphology. This study may provide new perspectives on the formation mechanism of carbonate morphogenesis in the process of biomineralization.

Synergistic effect of extracellular polymeric substances and carbon layer on electron utilization of Fe@C during anaerobic treatment of refractory wastewater

Nano zero-valent iron (NZVI) has been widely used to improve refractory wastewater treatment. However, the rapid dissolution of NZVI causes a waste of resources and an unstable bioaugmentation. Herein, to verify the essential role of slow release of NZVI on biological systems, a core-shell structured Fe@C composite was developed to demonstrate the long-term feasibility of Fe@C for enhancing azo dye biodegradation in comparison to a mixture of NZVI and carbon powder (Fe+C). The 150 days of long-term reactor operation showed that, although both Fe@C and Fe+C enhanced azo dye degradation, the former achieved a better performance than the latter. The strengthening effect of Fe@C was also more durable and stable than Fe+C. It may be due to the fact that the carbon layer of Fe@C could interact with extracellular polymeric substances (EPS) through physical adsorption and chemical bonding to form a stable buffer to regulate NZVI dissolution. The buffer layer could not only regulate the attack of H⁺ on NZVI to reduce its dissolution rate but also complex released Fe²⁺ and neutralize OH^- to alleviate the passivation layer formed on the NZVI surface. Moreover, microbial community analysis indicated that both Fe@C and Fe+C increased the abundance of fermentative bacteria (e.g., Bacteroidetes_vadinHA17, Propionicicella) and methanogens (e.g., Methanobacterium), but only Fe@C promoted the growth of azo dye degraders (e.g., Clostridium, Geobacter). Metatranscriptomic analysis further revealed that only Fe@C could substantially stimulate the expression of azoreductase and redox mediator (e.g., riboflavin, ubiquinone) biosynthesis involved in the extracellular degradation of azo dye. This work provides novel insights into the bioaugmentation of Fe@C for refractory wastewater treatment.

Complementary spectroscopy studies and potential activities of levan-type fructan produced by Bacillus paralicheniformis ND2

This study aimed at the production of marine bacterial exopolysaccharides (EPS) as biodegradable and nontoxic biopolymers, competing the synthetic derivatives, with detailed structural and conformational analyses using spectroscopy techniques. Twelve marine bacterial bacilli were isolated from the seawater of Mediterranean Sea, Egypt, then screened for EPS production. The most potent isolate was identified genetically as Bacillus paralicheniformis ND2 by16S rRNA gene sequence of ~99 % similarity. Plackett-Burman (PB) design identified the optimization conditions of EPS production, which yielded the maximum EPS (14.57 g L^-1) with 1.26-fold increase when compared to the basal conditions. Two purified EPSs namely NRF1 and NRF2 with average molecular weights (Mw¯) of 15.98 and 9.70 kDa, respectively, were obtained and subjected for subsequent analyses. FTIR and UV-Vis reflected their purity and high carbohydrate contents while EDX emphasized their neutral type. NMR identified the EPSs as levan-type fructan composed of β-(2-6)-glycosidic linkage as a main backbone, and HPLC explained that the EPSs composed of fructose. Circular dichroism (CD) suggested that NRF1 and NRF2 had identical structuration with a little variation from the EPS-NR. The EPS-NR showed antibacterial activity with the maximum inhibition against S. aureus ATCC 25923. Furthermore, all the EPSs revealed a proinflammatory action through dose-dependent increment of expression of proinflammatory cytokine mRNAs, IL-6, IL-1β and TNFα.

Mechanisms of interaction between polystyrene nanoplastics and extracellular polymeric substances in the activated sludge cultivated by different carbon sources

Nanoplastics (NPs) are ubiquitously present in wastewater treatment plants, which would be removed by the flocculation of extracellular polymeric substances (EPS) from activated sludge. However, the interaction mechanisms between NPs and EPS of activated sludge remain largely unexplored. This study investigated the interaction mechanisms between polystyrene nanoplastics (PS-NPs) and EPS with sodium acetate (NaAc), methanol (MeOH) and glucose (GLC) as carbon sources. The results showed that the functional group involved in the interactions between PS-NPs and EPS was the carbonyl of protein amide I region. The interaction between PS-NPs and EPS increased the β-sheets content, decreased the ratio of α-helix to (β-sheet + random coil), and changed the protein secondary structures to strong rigidity. This enhanced the flocculation of activated sludge cultivated by these three carbon sources. The flocculation between PS-NPs and EPS in activated sludge using NaAc as the carbon source was the strongest among these three carbon sources. Therefore, the degree of flocculation between NPs and EPS of activated sludge in wastewater treatment plants varies with carbon sources. This work provides a reference for the NPs removal mechanisms from wastewater, which will help to understand the migration behavior of MPs and NPs in wastewater treatment processes.

Direct observation of Mn distribution/speciation within and surrounding a basidiomycete fungus in the production of Mn-oxides important in toxic element containment

Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium. To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn²⁺ absorption by a basidiomycete fungus, Coprinopsis urticicola, isolated from Ningyo-toge mine water samples, was investigated in the laboratory under controlled conditions utilizing electron microscopy, synchrotron-based X-ray analysis, and fluorescence microscopy with a molecular pH probe. The fungus' growth was first investigated in an agar-solidified medium supplemented with 1.0 mmol/L Mn²⁺, and Cu²⁺ (0-200 μM), Zn²⁺ (0-200 μM), or diphenyleneiodonium (DPI) chloride (0-100 μM) at 25 °C. The results revealed that Zn²⁺ has no significant effects on Mn oxide formation, whereas Cu²⁺ and DPI significantly inhibit both fungal growth and Mn oxidation, indicating superoxide-mediated Mn oxidation. Indeed, nitroblue tetrazolium and diaminobenzidine assays on the growing fungus revealed the production of superoxide and peroxide. During the interaction of Mn²⁺ with the fungus in solution medium at the initial pH of 5.67, a small fraction of Mn²⁺ infiltrated the fungal hyphae within 8 h, forming a few tens of nm-sized concentrates of soluble Mn²⁺ in the intracellular pH of ∼6.5. After 1 day of incubation, Mn oxides began to precipitate on the hyphae, which were characterized as fibrous nanocrystals with a hexagonal birnessite-structure, these forming spherical aggregates with a diameter of ∼1.5 μm. These nanoscale processes associated with the fungal species derived from the Ningyo-toge mine area provide additional insights into the existing mechanisms of Mn oxidation by filamentous fungi at other U mill tailings sites under circumneutral pH conditions. Such processes add to the class of reactions important to the sequestration of toxic elements.

Complexing agents-free bioelectrochemical trickling systems for highly-efficient mesothermal NO removal: The role of extracellular polymer substances

The biological treatments are promising for nitric oxide (NO) reduction, however, the biotechnology has long suffered from high demands of NO-complexing agents (i.e., Fe(II)EDTA), leading to extra operation costs. In this study, novel complexing agents-free bioelectrochemical systems have been developed for direct NO reduction. The electricity-driven bioelectrochemical trickling system (ED-BTS, a denitrifying biocathode driven by the external electricity and an acetate-consuming bioanode) achieved approximately 68% NO removal without any NO-complexing agents, superior to the bioanode-driven BTS and open-circuit BTS. The extracellular polymeric substances from the biofilms of ED-BTS contained more polysaccharides, humic substrates, and hydrophobic tryptophan that were beneficial for NO reduction. Additionally, the external electricity altered the microbial community toward more denitrifying bacteria and a higher abundance of NO reduction genes (nosZ and cnorB). This study provides a comprehensive understanding of microbial behaviors on the adsorption and reduction of NO and proposes a promising strategy for mesothermal NO biotreatment.

The mechanism for enhancing phosphate immobilization on colloids of oxisol, ultisol, hematite, and gibbsite by chitosan

Phosphorus (P) availability in highly weathered soils is significantly influenced by the contents of iron (Fe)/aluminum (Al) oxides, clay minerals, and organic matter. With the increasing interest in biofertilizers (e.g. chitosan), it is important to understand how they affect P adsorption profiles on colloids of weathered soils rich in Fe/Al oxides. Thus, the effect of chitosan on the adsorption of P to colloids of hematite, gibbsite, Oxisol, and Ultisol was studied through electrokinetic measurements, spectroscopic analysis, and adsorption edge/isotherm profiles. The presence of chitosan significantly improved the surface positive charge and the decreasing trend of surface positive charge was slower for chitosan-treated colloids compared to the control with increasing pH. At pH 5.0, all the colloids were positively charged, with the oxides containing more positve charges than the soil colloids. At this pH value, the surface coverage capacity of P was 99.1, 61.6, 50.5, and 37.5 mmol kg⁻¹ for Oxisol, Ultisol, hematite, and gibbsite, respectively. This suggests that clay minerals in soil colloids were vital in enhancing P adsorption. In the presence of chitosan, the surface coverage capacity of P was increased by 111%, 173%, 647%, and 488% for Oxisol, Ultisol, gibbsite, and hematite, respectively. Drawing inferences from spectroscopic analysis, citric acid desorption profile, and zeta potential analysis, we suggest that chitosan (CH) enhanced P adsorption by promoting the formation of (i) citric acid "undisplaceable" inner-sphere P complexes such as [Colloid-OP-O-CH] and [Colloid-OP-N-CH], (ii) citric acid "displaceable" outer-sphere P complexes such as {[Colloid-O-CH]-OP} and {[Colloid-N-CH]-OP}, and (iii) water "leachable or soluble" P complexes such as {[Colloid-CH]⁺PO₄³⁻} and {[Colloid-OP]⁻CH⁺}. Thus, applying chitosan as a biofertilizer (source of N) along with P in highly weathered soils could improve P availability while reducing P leaching.

Performance and mechanism of nitrate removal by the aerobic denitrifying bacterium JI-2 with a strong autoaggregation capacity

Here, a new strain JI-2 of the strongly autoaggregating aerobic denitrifying bacteria was screened. The nitrate removal ability and autoaggregation mechanism of JI-2 were analyzed using the nitrogen balance and genomics technology. The nitrate removal rate was 27.05 mg N/(L·h) at pH 9.0 and C/N 8.0. The strain JI-2 removes nitrate via the aerobic denitrification and dissimilation pathways and removes ammonium via the assimilation pathway. 66.81 % nitrate was converted to cellular components under aerobic conditions. Complex nitrogen metabolism genes were detected in strain JI-2. C-di-GMP mediates the motility behavior of JI-2 by binding the FleQ and PilZ proteins, and regulating the expression of PslA. Furthermore, the mechanism of autoaggregation was verified by extracellular polymeric substance analysis. Meanwhile, the nitrate removal rates of strain JI-2 was 11.13-12.50 mg N/(L·h) in wastewater. Thus, strain JI-2 has good prospects for application in the treatment of nitrate wastewater.

Deciphering the underlying mechanism of MOF-808-based abiotic catalysis enhancing biodegradability of waste activated sludge: Insights from the effects on bioconversion of extracellular organic substances into methane

Extracellular organic substances (EOSs) usually control sludge biodegradability. Metal-organic framework-808 (MOF-808), a catalyst with a high ability of catalytic hydrolysis and proton transfer, has great potential to enhance biodegradability of EOSs. In this study, the underlying mechanism of MOF-808 enhancing the biodegradability of EOSs via abiotic catalysis was investigated. Experimental results showed that protein-like and humic acid-like substances were the main organic components in EOSs, and the MOF-808 enhanced the disintegration of protein-like substances rather than humic acid-like substances. Analyses of the changes in the functional group, the secondary structure of protein-like substances, and the electron transfer of catalytically degraded EOS samples revealed that the MOF-808 enhanced the hydrolysis of EOSs protein-like substances, loosened their secondary structure, and improved the electron transfer in EOSs. Further analyses of the MOF-808 before and after the catalysis reaction revealed that the coordination of Zr sites with protein-like substance-specific active sites (such as ZrN) in the MOF-808 substantially contributed to the high-efficiency catalysis. Biochemical methane potential assays confirmed that MOF-808-based abiotic catalysis promoted the generation efficiency of methane from the EOSs. These findings can elucidate the abiotic catalytic effect of MOF-808 on sludge biodegradability during the anaerobic digestion process.

Dewatering municipal wastewater sludge using electro-coagulation combined with added free nitrous acid

An electro-coagulation (EC) process combined with added free nitrous acid (FNA) improves sludge dewaterability. Under optimal conditions(EC voltage of 25 V, EC process time of 60 min, FNA dosage of 1.13 mg/L, pH value of 4.5), specific resistance to filtration (SRF) and water content (WC) was decreased by 89.57%, and 18.90%respectively. The EC process disrupted the sludge structure, reducing sludge particles' size (D50) from 59.5 to 50.5 μm. After adding FNA, the sludge cells lysed, and the DNA concentrations and soluble chemical oxygen demand (SCOD) increased from 6.07 μg/ml and 29 mg/L to 364 μg/ml and 588 mg/L, respectively. The conversion of Fe(II) to Fe(III) was enhanced. The addition of FNA after EC further improved the sludge dewaterability. Combined conditioning using EC and FNA can effectively destroy tightly bound extracellular polymeric substances (TB-EPS) and release bound water. In addition, the pH value is kept low, which benefits sludge dewaterability and the removal of heavy metals. The concentrations of Zn and Mn in the sludge cake were reduced by 92.3% and 69.0%, respectively. The Bureau of Reference (BCR) sequential extraction method showed increases in the percentages of the residual fractions of Zn and Mn, showing that EC combined with FNA is an efficient and versatile means of sludge conditioning.

Influence of graphene oxide on the toxicity of polystyrene nanoplastics to the marine microalgae Picochlorum sp

Graphene oxide (GO) features distinctive physical and chemical characteristics; therefore, it has been intensively investigated in environmental remediation as a promising material for clean-up of soil contamination and water purification and used as immobilization material. Plastic is a widespread pollutant, and its breakdown products such as nanoplastics (NPs) should be evaluated for potential harmful effects. This study is aimed to evaluate the influence of GO on the toxicity of polystyrene (PS) NPs to the marine microalgae Picochlorum sp. over a period of 4 weeks. The capability of GO to reduce the toxic effects of PS NPs was assessed through investigating exposure sequence of GO in the presence of 20 nm diameter-sized polystyrene NPs. This was accomplished through five test groups: microalgae pre-exposed to GO prior to incubation with PS NPs, microalgae post-exposed to GO after incubation with PS NPs, microalgae simultaneously exposed to GO and PS NPs, and individual exposure of microalgae to either GO or PS NPs. Cytotoxicity assay results demonstrated that microalgae pre-exposed to GO prior to incubation with PS NPs showed an increased viability and chlorophyll a content. The pre-exposure to GO has reduced the growth inhibition rate (IR) from 50%, for microalgae simultaneously exposed to GO and PS NPs, to 26%, for microalgae pre-exposed to GO. Moreover, the lowest level of reactive oxygen species (ROS) was recorded for microalgae exposed to GO only and microalgae pre-exposed to GO. Fourier-transform infrared (FTIR) analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) observations revealed some morphological changes of both algae and their extracellular polymeric substances (EPS) upon GO and PS NPs exposure combinations. The sequence of GO exposure to aquatic microorganisms might affect the level of harm caused by the PS NPs. Therefore, application of GO as part of an immobilization material and in the removal of pollutants from water should be carefully investigated using different pollutants and aquatic organisms.

Exposure to nanoplastic induces cell damage and nitrogen inhibition of activated sludge: Evidence from bacterial individuals and groups

Wastewater treatment plants (WWTPs) are almost the only place where plastic fragments are artificially removed, resulting in mass accumulation of nanoplastics (NPs). In this research, four different concentrations (0 mg/L, 0.1 mg/L, 1 mg/L, 10 mg/L) of polystyrene nanoplastics (PS-NPs) were used to investigate the cell damage and nitrogen inhibition of activated sludge, exposed in a self-assembled SBR reactor for 30 days. Intracellular reactive oxides (ROS) and extracellular lactate dehydrogenase (LDH) increased with the rise of exposure concentration, and morphological analysis disclosed the creases, collapse, and even rupture of cell membranes. However, exposure damage (PS-NPs ≤ 1 mg/L) appeared to be reversible, attributed to that extracellular polymeric substances (EPS) secretion can thicken the three protective layers outside the membrane. PS-NPs did not disrupt the EPS chemical structure, but increased humic acid content. Prolonged exposure time (from 15 to 30 days) was directly related to the nitrogen inhibition. Due to the habitat changes under PS-NPs exposure, abundance and diversity of microorganisms in the original activated sludge decreased significantly, and the dominant phylum was occupied by Patescibacteria (PS-NPs = 10 mg/L). Changes in enzyme activities of AMO, NR, NIR, and NOR with exposure concentration may explain the conversion of nitrogen in SBR. This research broadens our horizons to understand the response mechanism of activated sludge bacteria to PS-NPs exposure individually and collectively.

Feeding low-level benzethonium chloride can promote the start-up, fast recovery and long-term stable maintenance of partial nitrification for low-ammonium wastewater

The establishment of stable partial nitrification (PN) is beneficial to promote the application of anaerobic ammonium oxidation, especially for low-ammonium wastewater. This study demonstrated an innovative approach for achieving PN through feeding low-level benzethonium chloride (BZC). PN was started and maintained for 125 days after the sequential feeding of 0.2 and 1 mg/L BZC for 50 days. The damaged PN recovered rapidly within eight days by feeding 2 mg/L BZC, and it thrived for more than 172 days, indicating that nitrite-oxidizing bacteria did not adapt to BZC. The removal of BZC changed from adsorption to degradation gradually. Increased extracellular polymeric substances secretion and altered protein secondary structures explained sludge granulation during BZC feeding, which may be closely related to long-term stable maintenance of PN. PICRUSt2 revealed the underlying microbial mechanisms in depth. Overall, this research proposed a novel scheme to achieve robust PN treating low-ammonium wastewater through feeding low-level BZC.

The Multiple States of Environmental DNA and What Is Known about Their Persistence in Aquatic Environments

Increased use of environmental DNA (eDNA) analysis for indirect species detection has spurred the need to understand eDNA persistence in the environment. Understanding the persistence of eDNA is complex because it exists in a mixture of different states (e.g., dissolved, particle adsorbed, intracellular, and intraorganellar), and each state is expected to have a specific decay rate that depends on environmental parameters. Thus, improving knowledge about eDNA conversion rates between states and the reactions that degrade eDNA in different states is needed. Here, we focus on eukaryotic extraorganismal eDNA, outline how water chemistry and suspended mineral particles likely affect conversion among each eDNA state, and indicate how environmental parameters affect persistence of states in the water column. On the basis of deducing these controlling parameters, we synthesized the eDNA literature to assess whether we could already derive a general understanding of eDNA states persisting in the environment. However, we found that these parameters are often not being measured or reported when measured, and in many cases very few experimental data exist from which to draw conclusions. Therefore, further study of how environmental parameters affect eDNA state conversion and eDNA decay in aquatic environments is needed. We recommend analytic controls that can be used during the processing of water to assess potential losses of different eDNA states if all were present in a water sample, and we outline future experimental work that would help determine the dominant eDNA states in water.

High Mg/Ca Molar Ratios Promote Protodolomite Precipitation Induced by the Extreme Halophilic Bacterium Vibrio harveyi QPL2

Bacterial activities have been demonstrated as critical for protodolomite precipitation in specific aqueous conditions, whereas the relationship between the various hydrochemical factors and bacterial activity has not been fully explored. In this study, biomineralization experiments were conducted using a newly isolated extreme halophilic bacterium from salina mud, Vibrio harveyi QPL2, under various Mg/Ca molar ratios (0, 3, 6, 10, and 12) and a salinity of 200‰. The mineral phases, elemental composition, morphology, and crystal lattice structure of the precipitates were analyzed by XRD, SEM, and HRTEM, respectively. The organic weight and functional groups in the biominerals were identified by TG-DSC, FTIR, and XPS analysis. The amounts of amino acids and polysaccharides in the EPS of QPL2 cultured at various Mg/Ca molar ratios were quantified by an amino acid analyzer and high-performance liquid chromatography. The results confirm that disordered stoichiometric protodolomite was successfully precipitated through the activities of bacteria in a medium with relatively high Mg/Ca molar ratios (10 and 12) but it was not identified in cultures with lower Mg/Ca molar ratios (0, 3, and 6). That bacterial activity is critical for protodolomite formation as shown by the significant bacterial relicts identified in the precipitated spherulite crystals, including pinhole structures, a mineral coating around cells, and high organic matter content within the crystals. It was also confirmed that the high Mg/Ca molar ratio affects the composition of the organic components in the bacterial EPS, leading to the precipitation of the protodolomite. Specifically, not only the total EPS amount, but also other facilitators including the acidic amino acids (Glu and Asp) and polysaccharides in the EPS, increased significantly under the high Mg/Ca molar ratios. Combined with previous studies, the present findings suggest a clear link between high Mg/Ca molar ratios and the formation of protodolomite through halophilic bacterial activity.

Inhibition of Maillard reaction during alkaline thermal hydrolysis of sludge

The Maillard reaction (MR) occurs during the alkaline thermal hydrolysis (ATH) of sludge, which affects the quantity and quality of recovered protein. In this paper, four different sulfites were added to investigate their inhibitory effects on melanoidin production. The results showed that sulfites inhibited melanoidin production during ATH of sludge and the inhibitory rate increased with their concentration. At a concentration of 5.71 g/L, the inhibitory rates of NaHSO₃ on melanoidin were 63.27%. Furthermore, the 3D-EEM (Three-Dimension Excitation-Emission-Matrix) fluorescence spectroscopy and protein testing data showed that the inhibition of melanoidin production was accompanied by an increased protein concentration, and protein increased with increasing sulfites concentration. A 2.5-fold increase in protein concentration with Na₂S₂O₄ significantly enhanced the quantity of protein recovered. Therefore, the addition of sulfite during ATH of sludge reduces the amount of non-biodegradable melanoidin, which in turn benefits protein recovery.

Role of extracellular polymeric substances in the immobilization of hexavalent chromium by Shewanella putrefaciens CN32 unsaturated biofilms

Microbial remediation provides a promising avenue for the management and restoration of heavy metal-contaminated soils. Microorganisms in soils usually exist within unsaturated biofilms, however, their response to heavy metals is still limited compared to saturated biofilms. This work investigated the Cr(VI) immobilization by Shewanella putrefaciens CN32 unsaturated biofilms, and explored the underlying mechanisms of Cr(VI) complexation. Results reveal a dose-dependent toxicity of Cr(VI) to the growth of the unsaturated biofilms. During the early growth stage, the Cr(VI) addition stimulated more extracellular polymeric substances (EPS) production. In the meantime, the EPS were demonstrated to be the primary components for Cr(VI) immobilization, which accounted for more than 60% of the total adsorbed Cr(VI). The Fourier transform infrared spectra and X-ray photoelectron spectra corroborated that the binding sites for immobilizing Cr(VI) were hydroxyl, carboxyl, phosphoryl and amino functional groups of the proteins and polysaccharides in EPS. However, for the starved unsaturated biofilms, EPS were depleted and the EPS-bound Cr(VI) were released, which caused approximately 60% of the adsorbed Cr(VI) onto cell components and further aggravated the Cr(VI) stress to cells. This work extends our understanding about the Cr(VI) immobilization by unsaturated biofilms, and provides useful information for remediation of heavy metal-contaminated soils.

Flumequine-loaded titanate nanotubes as antibacterial agents for aquaculture farms

Flumequine (FLUM), a quinolone-derived antibiotic is one of the most prescribed drugs in aquaculture farms. However, its intensive use becomes worrisome because of its environmental risks and the emergence of FLUM-resistant bacteria. To overcome these problems we propose in this study the encapsulation and the delivery of FLUM by titanate nanotubes (TiNTs). Optimal FLUM loading was reached by suspending the dehydrated powder nanomaterials (FLUM : TiNTs ratio = 1 : 5) in ethanol. The drug entrapment efficiency was calculated to be 80% approximately with a sustained release in PBS at 37 °C up to 5 days. Then FLUM@TiNTs was evaluated for both its in vitro drug release and antimicrobial activity against Escherichia coli (E. coli). Spectacularly high antibacterial activity compared to those of free FLUM antibiotic was obtained confirming the efficiency of TiNTs to protect FLUM from rapid degradation and transformation within bacteria improving thereby its antibacterial effect. Indeed FLUM@TiNTs was efficient to decrease gradually the bacterial viability to reach ≈5% after 5 days versus ≈75% with free FLUM. Finally, the ex vivo permeation experiments on sea bass (Dicentrachus labrax) intestine shows that TiNTs act to increase the intestinal permeation of FLUM during the experiment. Indeed the encapsulated FLUM flux increased 12 fold (1.46 μg cm² h⁻¹) compared to the free antibiotic (0.18 μg cm² h⁻¹). Thanks to its physical properties (diameter 10 nm, tubular shape…) and its high stability in the simulated intestinal medium, TiNTs are easy internalized by enterocytes, thus involving an endocytosis mechanism, and then improve intestinal permeation of FLUM. Taken together, FLUM@TiNTs hold potential as an effective approach for enhancing the antimicrobial activity of FLUM and pave the way not only for future pharmacokinetic studies in the treatment and targeting of fish infections but also for instating of novel strategies that overcome the challenges associated with the abusive use of antibiotics in fish farming.

Flumequine (FLUM), a quinolone-derived antibiotic is one of the most prescribed drugs in aquaculture farms.

Influence of surface coatings on the adhesion of Shewanella oneidensis MR-1 to hematite

The adhesion of dissimilatory iron reducing bacteria (DIRB) to iron oxides is an important process to initiate direct extracellular electron transfer. Iron oxides in natural environments are often coated by organic matter or silica (SiO₂) which alters their surface physicochemical properties. To investigate the influence of these surface coatings, we characterized the dynamic adhesion processes of Shewanella oneidensis MR-1 to bare hematite, humic acid-coated hematite (hematite-HA), and SiO₂-coated hematite (hematite-SiO₂) using Quartz Crystal Microbalance with Dissipation (QCM-D). The molecular-level process and mechanism were investigated using in situ Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectrometry. We found that MR-1 formed a rigid bacterial layer on bare hematite. Coating with HA or SiO₂ decreased the surface cell density during the initial adhesion stage, and compromised the stability of the subsequent bacterial attachment. The FTIR combined with two-dimensional correlation spectroscopy (2D-COS) analysis showed that C-moieties of polysaccharides dominated interactions in initial adhesion on HA and SiO₂-coated hematite. In the longer term, the HA coating hindered the adsorption of amide, but promoted the binding of polysaccharide C-moieties to hematite. We concluded that, in general, both the HA and SiO₂ coatings reduced the attachment of MR-1 on hematite. These results advance our understanding of the roles of surface coatings on microbe-mineral interactions, which has significant implications for a series of biogeochemical processes in nature.

Effects of long-term perfluorooctane sulfonate (PFOS) exposure on activated sludge performance, composition, and its microbial community

The widespread presence and persistence of perfluorooctane sulfonate (PFOS) in wastewater treatment plants, as well as its toxicity and bioaccumulation potential, necessitates the investigation on their impact on bioreactor performance. A 48-day exposure test was adopted to study the effects of low (10 μg L-1) and high (1000 μg L-1) PFOS concentrations in a sequencing batch reactor on the performance, composition, and microbial community of activated sludge. The results suggested that adding PFOS at low and high concentrations lowered the removal efficiency of total nitrogen by 22.48% (p < 0.01) and 16.30% (p < 0.01) respectively, while enhanced that of total phosphorus by 1.87% (p > 0.05) and 7.07% (p < 0.05) respectively, compared with the control group. The addition of PFOS also led to the deterioration of activated sludge dewatering performance. Composition and spectroscopic measurements revealed that the PFOS dosage changed the composition of the activated sludge. Furthermore, the PFOS altered the structure and function of the activated sludge microbial community as well as key enzyme activities.

Functional group diversity for the adsorption of lead(Pb) to bacterial cells and extracellular polymeric substances

Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources.

Insight into correlation of advanced nitrogen removal with extracellular polymeric substances characterization in a step-feed three-stage integrated anoxic/oxic biofilter system

As a core component of the biomass, the important role of extracellular polymeric substances (EPS) on treatment performance has been recognized. However, the comprehensive understanding of its correlation with nitrogen removal remains limited in biofilm-based reactors. In this study, the relevance between EPS and advanced nitrogen removal in a novel step-feed three-stage integrated anoxic/oxic biofilter (SFTIAOB) was specifically investigated. The operation showed as high as 81% TN removal was achieved under optimal conditions. Among the whole reactor, 2nd anoxic (A2) zone was the largest contributor for nitrogen removal, followed by the 3rd anoxic (A3) and 2nd oxic (O2) zones. EPS composition analysis found that high content of polysaccharides in tightly bound-EPS (A2 and A3) and protein in loosely bound-EPS and tightly bound-EPS (O2). Fourier transform infrared spectroscopy, three-dimensional fluorescence spectrum further verified stratified EPS subfractions containing different secondary protein structures, while 3-turn helix and tryptophan-like protein was the main reason for nitrogen removal. High-throughput sequencing revealed the co-existence of nitrogen removal-associated genera accomplished nitrification/denitrification combined with aerobic denitrification and anammox. Moreover, the correlation of EPS and microbial composition with nitrogen removal was clarified by redundancy analysis (RDA). Finally, potential mechanism for nitrogen removal was illuminated. This research gives more insight into EPS characteristics in enhancing nitrogen removal during the operation and optimization of a step-feed multi-stage A/O biofilm process.

Polysorbate-80 pretreatment contributing to volatile fatty acids production associated microbial interactions via acidogenic fermentation of waste activated sludge

Polyoxyethylene dehydration sorbitol monooleate (polysorbate-80) pretreatment enhanced volatile fatty acids (VFAs) production of waste activated sludge (WAS) in acidogenic fermentation. The results showed that polysorbate-80 ameliorated WAS solubilization obviously with a soluble chemical oxygen demand (SCOD) increasing to 1536 mg/L within 4 h. Within 2 days of acidogenic fermentation, the maximal VFAs arrived to 2958.35 mg COD/L via polysorbate-80-pretreatment. The polysorbate-80 pretreatment boosted microbial diversity and richness in fermentation process. The Clostridium, Macellibacteroides and Acidocella strengthened microbial cooperation for the metabolic functions enhancement (e.g. amino acid metabolism and carbohydrate metabolism) for VFAs generation from WAS organics. Overall, the polysorbate-80 could play positive roles on the transformation of organic matter from sludge solid matters to VFAs, which was turned out to become an effective enhancing strategy for future WAS treatment / bioresource recovery with relatively low cost.

Humic acid enhanced pyrene degradation by Mycobacterium sp. NJS-1

The search for nature-based tools to enhance bioremediation is essential for the sustainable restoration of contaminated ecosystems. Humic acid (HA) is an important component of organic matter in soil and water, but its effect on the microbial degradation of organic pollutants remains unclear. In this study, the biodegradation of pyrene by Mycobacterium sp. NJS-1 with and without HA was investigated. Only around 10.5% of pyrene was biodegraded in the pyrene treatment alone, whereas the addition of HA significantly enhanced biodegradation to the point where over 90% of pyrene was biodegraded. The production of 4,5-dihydropyrene-4,5-diol and phenanthrene-3,4-diol indicated the metabolic pathway via attacking of 4,5-positions of pyrene. Interestingly, 1,2-dimethoxypyrene was detected with the addition of HA, suggesting that HA induced a new ring-opening pathway involving the attack on the 1,2-positions of pyrene. The addition of HA first induced protein self-cleavage behavior with a significant increase in phenylalanine, tyrosine, and tryptophan containing large numbers of COO^- groups. Furthermore, it altered the intracellular and extracellular ultrastructure of bacterial cells, promoting their growth in size and number as well as reducing the space between them. Overall, HA increased the ring-opening positions of pyrene and facilitated its interaction with bacterial cells, thus improving its biodegradability. Building upon the findings of this study to further research is conducive to the sustainable solution of environmental pollution.

The responses of activated sludge to membrane cleaning reagent H2O2 and protection of extracellular polymeric substances

Hydrogen peroxide (H₂O₂) is evaluated as a potential replacement for chlorine to control biofouling in membrane bioreactors (MBRs). However, H₂O₂ might diffuse into the mixed liquor and damage microorganisms during membrane cleaning. This study comprehensively analyzed the impacts of H₂O₂ on microbes. Key enzymes involved in phenol biodegradation were inhibited with H₂O₂ concentration increased, and thus phenol degradation efficiency was decreased. Increase of lactic dehydrogenase (LDH) and intracellular reactive oxygen species (ROS) indicated more severe cell rupture with H₂O₂ concentration increased. At the same H₂O₂ concentration, Extracellular polymeric substances (EPS) extraction further led to inhibiting the activity of key enzymes, decreasing phenol degradation efficiency, and enhancing LDH release and ROS production, demonstrating that the existence of EPS moderated the adverse impacts on microbes. Spectroscopic characterization revealed the increase of H₂O₂ decreased tryptophan protein-like substances, protein-associated bonds and polysaccharide-associated bonds. Hydroxyl and amide groups in EPS were attacked, which might lead to the consumption of H₂O₂, indicated EPS protect the microorganism through sacrificial reaction with H₂O₂.

Genetic optimisation of bacteria-induced calcite precipitation in Bacillus subtilis

Background

Microbially induced calcite precipitation (MICP) is an ancient property of bacteria, which has recently gained considerable attention for biotechnological applications. It occurs as a by-product of bacterial metabolism and involves a combination of chemical changes in the extracellular environment, e.g. pH increase, and presence of nucleation sites on the cell surface or extracellular substances produced by the bacteria. However, the molecular mechanisms underpinning MICP and the interplay between the contributing factors remain poorly understood, thus placing barriers to the full biotechnological and synthetic biology exploitation of bacterial biomineralisation.

Results

In this study, we adopted a bottom-up approach of systematically engineering Bacillus subtilis, which has no detectable intrinsic MICP activity, for biomineralisation. We showed that heterologous production of urease can induce MICP by local increases in extracellular pH, and this can be enhanced by co-expression of urease accessory genes for urea and nickel uptake, depending on environmental conditions. MICP can be strongly enhanced by biofilm-promoting conditions, which appeared to be mainly driven by production of exopolysaccharide, while the protein component of the biofilm matrix was dispensable. Attempts to modulate the cell surface charge of B. subtilis had surprisingly minor effects, and our results suggest this organism may intrinsically have a very negative cell surface, potentially predisposing it for MICP activity.

Conclusions

Our findings give insights into the molecular mechanisms driving MICP in an application-relevant chassis organism and the genetic elements that can be used to engineer de novo or enhanced biomineralisation. This study also highlights mutual influences between the genetic drivers and the chemical composition of the surrounding environment in determining the speed, spatial distribution and resulting mineral crystals of MICP. Taken together, these data pave the way for future rational design of synthetic precipitator strains optimised for specific applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01704-1.

Facile synthesis of silver modified zinc oxide nanocomposite: An efficient visible light active nanomaterial for bacterial inhibition and dye degradation

The present study reports the synthesis of silver (Ag) decorated zinc oxide (ZnO) nanocomposite via green synthesis method by using Acacia arabica plant leaves extract as both reducing and capping agent. The results clearly indicate a uniform distribution of Ag nanoparticles (NPs) over ZnO surface. Various analytical and spectroscopic techniques were used for investigating the formation and morphology of as-synthesized Ag/ZnO nanocomposites. Emergence of SPR at 424 and 378 nm confirmed the synthesis of AgNPs and ZnO respectively. The confirmation of elemental composition and crystal structure of prepared nanomaterials (NMs) was carried out via EDX and XRD analysis. Results obtained from HRTEM and SEM analysis indicated small sized spherically shaped NMs. The as-synthesized was checked for its photocatalytic activity towards degradation of MB in the presence as well as absence of light irradiation. Results of degradation study revealed that Ag/ZnO exhibits remarkable photocatalytic activity in the presence of light whereby removing 90% of MB within 80 min. Moreover, the antibacterial activity of synthesized nanocomposite was examined in both visible light and dark conditions. The experiment showed that nanomaterial depicts enhanced antibacterial activity in light in comparison to dark. The results showed that the inhibition diameter of Ag/ZnO nanocomposite in light was found to be 18 (±0.2), 22 (±0.3) against E. coli and S. aureus respectively. The inhibition zone of the said nanomaterial against E. coli and S. aureus in dark was 11 (±0.3), 14 (±0.5) respectively. These results conclude that activity is delivered both in the presence of visible light and dark but efficiency of antibacterial activity is found to be more in visible light in comparison.

High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces

The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu₂O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu₂O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).

Holistic insights into extracellular polymeric substance (EPS) in anammosx bacterial matrix and the potential sustainable biopolymer recovery: A review

Anaerobic ammonia oxidation (anammox) process has been proven to be a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loading rates. Anammox process is mainly operated through biofilm or granular sludge structures, as for such slow-growing microorganisms, elevated settling velocity of granules allows for adequate biomass retention and lowered potential risk of washouts. Stability of granular sludge biomass is extremely critical, yet the formation mechanism is poorly understood. There are number of important functions linked to Extracellular Polymeric Substance (EPS) in anammox bacterial matrix, such as; structural stability, aggregation promotion, maintenance of physical structure in the granules, water preserving and protective cell barrier. There is an increasing demand to introduce accurate methods for proper EPS extraction and characterization, to expand the perception of anammox granule stability and potential resource recovery. Analyzing EPS with a focus on various (mechanical and physical) properties can lead to biopolymer production from granular sludge. Biopolymers such as EPS are attractive alternatives substituting the conventional chemical polymers furthermore their recovery from the waste sludge and the potential applications in industrial sectors, leads to a radical enhancement of both environmental and economical sustainability, accelerating the circular economy advancements. Here, this study aims to overview the newest understanding on the structure of anammox sludge EPS, obtained recently and to assess the potential challenges and prospects to identify the knowledge gaps towards constructing an inclusive anammox EPS recovery and characterization procedure.