Amount Of Extracellular Polymeric Substances Research Articles

Study on treatment of chemical plant wastewater by using a integrated anaerobic–aerobic bioreactor

ABSTRACT In this work, a new type of integrated anaerobic aerobic bioreactor (IAAB) was formed by optimizing the structure of the anaerobic baffle bioreactor and aerobic biological contact oxidation pool. IAAB was used to treat the production wastewater of a chemical plant. The whole process was divided into two stages of domestication and stable operation. With increasing the proportion of chemical wastewater, the total amount of extracellular polymeric substances increased, and the ratio of protein to polysaccharide decreased. Dehydrogenase activity of anaerobic granular sludge in each compartment increased about 1.5 times with time, and decreased about 42% along the flow direction from the first compartment to the third compartment. The coenzyme F420 increased about 4 times with time, and increased about 1.2 times along the flow direction. The IAAB showed excellent removal rate of chemical oxygen demand (85%), ammonia nitrogen (94%), nitrobenzenes (98%).

Effects of lysed sludge reflux point on ultrasound lysis-cryptic growth in anaerobic/aerobic (A/O) wastewater treatment: Sludge reduction, microbial community, and metabolism

Ultrasonication allows sludge reduction to be performed in situ during wastewater treatment, and the reflux point of the lysed sludge affects this performance. This study investigated the effects of reflux point (anaerobic stage, carbon/nitrogen (C/N) lowest stage, and aerobic stage) on sludge lysis-cryptic growth in an anaerobic/aerobic reactor and variations in the sludge and microbial community. The best reflux point occurred at the lowest C/N ratio stage, and a 50.96% reduction in excess sludge was achieved. The reflux of the lysed sludge to the aerobic stage reduced nitrogen and phosphorus removal. The reflux of the lysed sludge decreased the average sludge size, reaching 29.2 μm when reflux to the aerobic stage. Scanning electron microscopy showed that the sludge surface was unaffected by the reflux point. The Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy results showed that the most prominent variation in the intensity of the sludge functional groups occurred when the reflux was at the lowest C/N stage. The amount of extracellular polymeric substances decreased the most during reflux to the anaerobic stage. The sludge microbial communities varied with the reflux point, and the dominant phyla during reflux to the anaerobic, lowest C/N, and aerobic stages were Bacteroidetes, Firmicutes, and Bacteroidetes, respectively. Furthermore, the reflux point did not alter the metabolic pathway of sludge microorganisms but increased the number of enzymes in metabolic pathways.

Native microalgae and Bacillus XZM remediate arsenic-contaminated soil by forming biological soil crusts

Biological soil crusts (BSCs) are a useful tool for immobilization of metal(loid)s in mining areas. Yet, the typical functional microorganisms involved in promoting the fast development of BSCs and their impacts on arsenic(As) contaminated soil remain unverified. In this study, As-contaminated soil was inoculated with indigenous Chlorella thermophila SM01 (C. thermophila SM01), Leptolyngbya sp. XZMQ, isolated from BSCs in high As-contaminated areas and plant growth-promoting (PGP) bacteria (Bacillus XZM) to construct BSCs in different manners. After 45 days of ex-situ culture experiment, Leptolyngbya sp. XZMQ and bacteria could form obvious BSCs. Compared to single-inoculated microalgae, the co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased soil pH and water content by 10% and 26%, respectively, while decreasing soil EC and density by 19% and 14%, respectively. The soil catalase, alkaline phosphatase, sucrase, and urease activities were also increased by 30.53%, 96.24%, 154.19%, and 272.17%, respectively. The co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM drove the formation of BSCs by producing large amounts of extracellular polymeric substances (EPS). The three-dimensional fluorescence spectroscopy (3D-EEM) analysis showed that induced BSCs increased As immobilization by enhancing the contents of tryptophan and tyrosine substances, fulvic acid, and humic acid in EPS. The presence of the –NH2 and –COOH functional groups in tryptophan residues were determined using Fourier Transform Infrared Spectroscopy (FTIR). X-Ray Diffraction (XRD) analysis showed that there were iron (hydrogen) oxides in BSCs, which could form ternary complexes with humic acid and As, thereby increasing the adsorption of As. Therefore, BSCs formed by co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased the immobilization of As, thereby reducing the content of soluble As in the environment. In summary, our findings innovatively provided a new method for the remediation of As-contaminated soil in mining areas.

Pollutants removal and connections among sludge properties, metabolism potential and microbial characteristics in aerobic granular sequencing batch reactor for petrochemical wastewater treatment

Petrochemical wastewater contains inhibitory compounds such as aromatics that are toxic to microorganisms during biological treatment. The compact and layered structure and the high amount of extracellular polymeric substances (EPS) in aerobic granular sludge (AGS) can contribute to protecting microorganisms from the harsh environment. This study evaluated the changes in the granule properties, pollutants removal, microbial metabolic potential and molecular microbial characteristics of the AGS process for petrochemical wastewater treatment. Granules treating petrochemical wastewater had a higher SVI30/SVI5 value (0.94) than that treating synthetic wastewater. An increase in bioactivity and EPS secretion with higher bio-polymer composition, specifically the functional groups such as hydroxyl, alkoxy and amino in protein, was observed, which promoted biomass aggregation. The granules also had more than 2-fold higher specific oxygen utilization rate. The AGS-SBR process obtained an average COD removal of 93% during petrochemical wastewater treatment and an effluent bCOD of below 1 mg L−1. No obvious inhibition of nitrification and denitrification activity was observed in the processes attributed to the layered structure of AGS. The average effluent NH4+-N of 5.0 mg L−1 was obtained and TN removal efficiencies of over 80.0% was achieved. Molecular microbial analysis showed that abundant functional genera Stenotrophomonas and Pseudoxanthomonas contributed to the degradation of aromatics and other petroleum organic pollutants. They were enriched with the variation of group behavior while metabolisms of amino acids and carboxylic acids by the relevant functional genera (e.g., Cytophagia) were significantly inhibited. The enrichment of Flavobacterium and Thermomonas promoted nitrification and denitrification, respectively. This research revealed the rapid start-up, enhanced granule structural strength, high inhibition resistance and considerable performance of AGS-SBR for petrochemical wastewater treatment.

Inductive effect of functional microbial consortia in promoting the rapid granulation of aerobic granular sludge in an internal circulation-membrane bioreactor

The added functional microbial consortia (SAB) was found to accelerate the formation of aerobic granular sludge (AGS) in a continuous experiment lasting 150 days, where the primary AGS was first observed on day 7 and the bioreactor was started-up very quickly and performed well in removing the main pollutants. According to the obtained results, Streptomyces sp. Esraa could form a skeleton to support the formation of AGS, while Bacillus cereus aggregated microorganisms by secreting a large amount of extracellular polymeric substances (mainly protein) continuously, and extracellular polymeric substances immediately increase from 97 mg/gMLVSS to 1551 mg/gMLVSS. With the succession of microbial community, the abundance of Streptomyces and Bacillus in sludge decreased significantly on day 21, from 43.22% to 1.78% and from 5.87% to 0, respectively, while the abundance of Bacillus in AGS remained 0.1% on day 120, and SAB was gradually replaced by other dominant microorganisms, which indicated that the added SAB exhibited an inductive effect on the formation of AGS.

Sulfide inhibition on polyphosphate accumulating organisms and glycogen accumulating organisms: Cumulative inhibitory effect and recoverability

Sulfate in wastewater can be reduced to sulfide and its impact on the stability of enhanced biological phosphorus removal (EBPR) is still unclear. In this study, the metabolic changes and subsequent recovery of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) were investigated at different sulfide concentrations. The results showed that the metabolic activity of PAOs and GAOs was mainly related to H2S concentration. Under anaerobic conditions, the catabolism of PAOs and GAOs was promoted at H2S concentrations below 79 mg/L S and 271 mg/L S, respectively, and inhibited above these concentrations; whereas anabolism was consistently inhibited in the presence of H2S. The phosphorus (P) release was also pH-dependent due to the intracellular free Mg2+ efflux from PAOs. H2S was more destructive to the esterase activity and membrane permeability of PAOs than those of GAOs and prompted intracellular free Mg2+ efflux of PAOs, resulting in worse aerobic metabolism and subsequent recovery of PAOs than GAOs. Additionally, sulfides facilitated the production of extracellular polymeric substances (EPS), especially tightly bound EPS. The amount of EPS in GAOs was significantly higher than that in PAOs. The above results indicated that sulfide had a stronger inhibition to PAOs than GAOs, and when sulfide was present, GAOs had a competitive advantage over PAOs in EBPR.

Assessment of the MICP potential and corrosion inhibition of steel bars by biofilm forming bacteria in corrosive environment

The porous network and micro-cracks of concrete facilitate the movement of deleterious ions inside the concrete cover which could corrode the embedded steel. The calcifying bacteria fill up the pore spaces and cracks through a self-healing mechanism, however their capability to precipitate CaCO3 in chlorides rich environment and impact on the corrosion of rebars was unknown. Therefore, the influence of 0%–5% NaCl contents was investigated on the CaCO3 producing capability of four Bacillus strains in this study. In addition, corrosion attributes of steel bars were explored upon interacting with bacteria in the simulated cracked concrete exposed to the 3.5% NaCl solution. The results indicated that on average 1.5% of NaCl content positively affects the bacterial CaCO3 production capability and B. subtilis and B. pumilus produced more CaCO3 at 7 days and 15 days, respectively. Besides, increase in NaCl content significantly altered the type of produced CaCO3 polymorph, microstructure, and crystallinity. The bacterial biofilm forming potential and effect of biofilm on corrosion of steel bars was evaluated through Tafel polarization and electrochemical impedance spectroscopy. The B. subtilis and B. safensis were the optimum strains in developing strong and sticky biofilms during both in-vitro and in-vivo studies and appeared as excellent corrosion inhibitors of reinforcing steel bars compared to the control specimen under an exposure of 3.5% NaCl. Increase in the concentration of NaCl aggregated more bacterial cells together and resulted in the secretion of maximum amount of extracellular polymeric substances. Besides, the biofilm formed by B. safensis was comparatively more uniform and thicker without any blemishes thus considered optimum strain to prevent the corrosion of rebars.

Phototransformation of extracellular polymeric substances in activated sludge and their interaction with microplastics.

Substantial amounts of extracellular polymeric substances (EPS) are present in sludge from wastewater treatment plants (WWTP), and EPS can significantly affect the fate, bioavailability, and toxicity of microplastics (MPs) that coexist in the effluent, however, the mechanism of action between EPS and microplastics remains unclear. In addition, ultraviolet (UV) disinfection is indispensable in the wastewater treatment process in WWTP, which can significantly affect the characteristics of EPS. Therefore, it is of great significance to study the photochemical characteristics of EPS and the effect on binding MPs. In this study, using multispectral technology and two-dimensional correlation spectroscopy analysis, indicates that the molecular weight and aromaticity of EPS after phototransformation were reduced. The results showed that the adsorption of EPS on PSMPs was in the order of TB-EPS > LB-EPS > S-EPS, which was positively correlated with the SUVA254, but negatively correlated with O/C of EPS. This indicates that the main adsorption mechanisms of PSMPs on EPS were π-π and hydrophobicity. The adsorption capacity of S-EPS, LB-EPS and TB-EPS to PSMPs decreased with the increasing of illumination time. After phototransformation, the adsorption sensitivity and reaction sequence of EPS and PSMPs did not change much. This research provides a theoretical basis for understanding the photochemical transformation of extracellular polymers and the morphology and migration of microplastics in sewage treatment, and evaluating the impact of microplastics on ecosystems.

Bioreduction of Cr(VI) using a propane-based membrane biofilm reactor.

The strong physiological toxicity of Cr(VI) makes it widely concerned in wastewater treatment. At present, the simplest and harmless method for treating Cr(VI) is known to be biologically reducing it to Cr(III), making it precipitate as Cr(OH)3(s), and then removing Cr(III) by solid separation technology. Studies have shown that Cr(VI) reduction bacteria can use CH4 and H2 as electron donors to reduce Cr(VI). Based on this, in this study, C3H8 was used as the only electron donor to investigate the potential of C3H8 matrix membrane bioreactor in the Cr(VI) wastewater treatment. The experiment was divided into three stages, each of which run stably for at least 30days, and the whole process run for 120days in total. The experiment is divided into three stages, each stage runs stably for at least 30days, for a total of 120days. With the increase of the Cr(VI) load, the removal rate gradually decreased. In stage 3, when Cr(VI) concentration was 2.0mg·L-1, the removal rate was reduced from 90% in the first stage to 75%. According to X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis, it is known that Cr(III) is the main product during this process and it is adsorbed on the biofilm as Cr(OH)3 precipitate. During the experiment, the amount of extracellular polymeric substance (EPS) produced by microorganisms increased initially and then decreased, and the amount of polysaccharides (PS) was always more than protein (PN). By analyzing the microbial community structure after inoculating sludge and adding Cr(VI), Nocardia and Rhodococcus dominate the biofilm samples. Chromate reductase, cytochrome c, nitrate reductase, and other functional genes related to chromate reductase increased gradually during the experiment.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

ABSTRACT Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Exploration of the dynamic osmotic membrane bioreactor in low-speed rolling motion for membrane fouling mitigation

A specific dynamic osmotic membrane bioreactor (DR-OMBR) in low-speed rolling motion was designed to alleviate membrane fouling. Using a low rotation speed (2 rpm) together with the cross-flow velocity in this designed DR-OMBR, the shear stress (−1.57 × 10−4 N/m2) and the centrifugal force (1.31 × 10−4 N) were generated to reduce the attachment of foulant to the membrane surface and achieve a relatively stable water flux. A parallel experiment indicated that the water flux of the conventional OMBR (without rotation) was 10% lower than that of the DR-OMBR, and total organic carbon and phosphate removals still achieved 99.9 and 97.0%, respectively. The ammonium rejection was slightly lower as a result of the Donna effect. Furthermore, compared to rotation speeds (0–5 rpm), the rotation speed of 2 rpm achieved better water flux (6.4 LMH) and lower reversal salt diffusion (3.7 gMH) because the centrifugal force had a positive effect on the reversal salt flux and a negative impact on the water flux, and a higher rotation speed could generate a considerable centrifugal force to limit the water flux and increase the reverse salt flux. Furthermore, the mitigation of membrane fouling was further confirmed by the relatively low amount of extracellular polymeric substances (EPS) and soluble microbial products (SMP) on the membrane surface of the DR-OMBR.

The effects of salinity changes on anammox performance: The response rule and tolerance mechanism.

Some wastewaters contain high concentrations of ammonia coexisting with large amounts of salt, which might negatively affect the anaerobic ammonium oxidation (anammox) process. In this study, the performance of the anammox process under different saline conditions was investigated using an upflow anaerobic sludge bed-anammox system. After long-term operating for 275 days, the results indicated that the nitrogen removal efficiency remained high under the 0-40 g NaCl/L, and low salinity (15 g NaCl/L) substantially promoted specific anammox activity. Affected by the saline environment, the appearance, color, and shape of sludge notably changed, and the amount of extracellular polymeric substances gradually increased with increasing salinity, which might be one of the reasons for the strong salt tolerance of the system. Chloroflexi and Planctomycetes were the dominant strains under long-term salinity, and Brocadiaceae_g_ unclassified exhibited halophilic characteristics. The redundancy analysis results showed that the concentration of influent NH4 + -N and salinity were the main environmental factors affecting the microbial community of the system. PRACTITIONER POINTS: Provides data to support the maximum value for salinity wastewater treatment with anammox processes' tolerance of 40 g NaCl/L. EPS changes may be responsible for the response to salinity challenges and provide direction for high salinity wastewater treatment. Brocadiaceae_g_ unclassified exhibited a halophilic quality. And it can be focused on to improve treatment efficiency.

Membrane fouling mitigation by coagulation and electrostatic repulsion using an electro-AnMBR in kitchen wastewater treatment

Anaerobic membrane bioreactor (AnMBR) is considered an efficient technique for kitchen wastewater treatment; however, membrane fouling restricts their applicability. In this study, a novel AnMBR with an Fe anode and Ti membrane cathode (electro-AnMBR) was constructed. The reactor exhibited good performance in pollutant removal and antifouling in kitchen wastewater treatment. Compared with the traditional AnMBR, the electro-AnMBR increased phosphate removal by approximately 55% and reduced transmembrane pressure (TMP) by 50%. Coagulation from the Fe2+/Fe3+ released by the sacrificial anode increased the sludge floc size and porosity, significantly reducing the membrane fouling potential. In addition, the lower amounts of extracellular polymeric substances (EPS) in the electro-AnMBR, due to an increased Methanosarcina abundance, facilitated membrane-fouling mitigation. Almost no TMP difference was observed between the AnMBRs with Ti, ceramic, and polyvinylidene fluoride (PVDF) membranes. Quantitative analysis using an electrochemical quartz crystal microbalance with dissipation monitoring indicated that the electrostatic repulsion between EPS and cathodic membrane was positively correlated with the applied voltage. In addition, proteins in EPS had a higher membrane fouling potential than polysaccharides, and Fe3+ coagulation reduced adhesion capacity and alleviated membrane fouling. This study provides a perspective viewpoint for AnMBR membrane fouling mitigation and reactor design.

Algal extracellular organic matter pre-treatment enhances microalgal biofilm adhesion onto microporous substrate

Adhesive biocoating has microstructure composed of biomolecules to entrap viable cells in a stabilized matrix over exposed surfaces. Although marine benthic diatoms are a common group of algae excreting substantial amount of extracellular polymeric substances (EPS), studies regarding the utilization of these EPS are scarce. Using the soluble EPS derived from Navicula incerta and pre-deposition of it as a thin conditioning layer on microporous polyvinylidene fluoride (PVDF) membranes, the pre-coated surface was used to investigate the cell binding affinity of three marine microalgae, namely Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta. Microalgae actively engaged themselves on the pre-coated membranes which was 10 times greater than the initial cell adhesion degree. Soluble EPS is mainly comprised of polysaccharide while bounded EPS is mainly comprised of protein. On EPS pre-coated membranes, N. incerta released the least amount of bounded polysaccharides (<100 mg m−2) and vice versa for the other two because EPS production is usually maximized to assist cell adhesion onto unfavorable substrates. In stark contrast, when the adaptation period (first 6 h) ended, cells began to secrete more bounded protein for cell growth, and an increasing trend of protein content found in N. incerta has verified its optimal adaptation onto the biocoating itself. On pristine PVDF membranes, the adhesion degree was ranked in ascending order: C. fusiformis, N. incerta and A. coffeaeformis. Interestingly, after the pre-coating process, the order was reported as: A. coffeaeformis, N. incerta and C. fusiformis, but it should be noted that C. fusiformis demonstrated fluctuating cell colonization degree and bounded EPS production over time. In other words, the biofilm's susceptibility was confirmed since the cells latched loosely on the membranes rather than in a biofilm matrix. Biocoating enables uniform cell distribution and firmer biofilm growth, opening the door to vast future applications in environmental bioremediation and sensing.

Cadmium-resistant Chryseobacterium sp. DEMBc1 strain: characteristics and potential to assist phytoremediation and promote plant growth.

The effectiveness of phytoremediation is closely related to the various interactions between pollutants, soil particles, rhizosphere microorganisms, and plants. Therefore, the object of current study was a cadmium-tolerant bacterium isolated from the rye rhizosphere, with a high degree of genetic similarity to the genus Chryseobacterium. Chryseobacterium sp. DEMBc1 was able to grow with 36 different BiologGN2 carbon sources and show the adaptation to stress factors such as Cd (100 μg ml-1), low temperature (8 °C), and salinity (2% NaCl). Furthermore, it was shown that DEMBc1 had the characteristics of plant growth-promoting microorganisms: it was able to produce ammonia, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase, and siderophores, as well as solubilize Ca3(PO4)3. After inoculation with DEMBc1, a significant decrease in the concentration of Cd was observed in the roots of Festuca ovina grown in Cd-polluted soil, compared to the non-inoculated Cd-polluted soil. It was also noticed that DEMBc1 produced a large amount of extracellular polymeric substances that were significantly higher than the cellular biomass. These polymers can form a barrier to reduce the translocation of Cd from the growth medium to the plant roots. According to the current study, DEMBc1 has a stabilizing potential and can decrease the mobility of Cd in the F. ovina rhizosphere, bioaccumulate metals in plant tissues, and effectively improve the bioavailability of nutrients, especially Fe, N, and P in a polluted environments.

Effects of Pressurized Aeration on the Biodegradation of Short-Chain Chlorinated Paraffins by Escherichia coli Strain 2.

Short-chain chlorinated paraffins (SCCPs) were defined as persistent organic pollutants in 2017, and they can migrate and transform in the environment, accumulate in organisms, and amplify through the food chain. Although they pose a serious threat to environmental safety and human health, there are few papers on their removal. The current SCCP removal methods are expensive, require severe operating conditions, involve time-consuming biological treatment, and have poor removal specificities. Therefore, it is important to seek efficient methods to remove SCCPs. In this paper, a pressurized reactor was introduced, and the removal performance of SCCPs by Escherichia coli strain 2 was investigated. The results indicated that moderate pure oxygen pressurization promoted bacterial growth, but when it exceeded 0.15 MPa, the bacterial growth was severely inhibited. When the concentration of SCCPs was 20 mg/L, the removal rate of SCCPs was 85.61% under 0.15 MPa pure oxygen pressurization for 7 days, which was 25% higher than at atmospheric pressure (68.83%). In contrast, the removal rate was only 69.28% under 0.15 MPa air pressure. As the pressure continued to increase, the removal rate of SCCPs decreased significantly. The total amount of extracellular polymeric substances (EPS) increased significantly upon increasing the pressure, and the amount of tightly bound EPS (TB-EPS) was higher than that of loosely bound EPS (LB-EPS). The pressure mainly promoted the secretion of proteins in LB-EPS. Furthermore, an appropriate pure oxygen pressure of 0.15 MPa improved the dehydrogenase activity. The gas chromatography–mass spectrometry (GC–MS) results indicated that the degradation pathway possibly involved the cleavage of the C–Cl bond in SCCPs, which produced Cl−, followed by C–C bond breaking. This process degraded long-chain alkanes into short-chain alkanes. Moreover, the main degradation products detected were 2,4-dimethylheptane (C9H20), 2,5-dimethylheptane (C9H20), and 3,3-dimethylhexane (C8H18).

Pioneer species of Cyanobacteria in hot springs and their role to travertine formation: The case of Aedipsos hot springs, Euboea (Evia), Greece

AbstractCyanobacteria are considered to be among the first microorganisms to settle in hot springs where they form a favourable environment for further biological establishment. Nevertheless, the exact pioneer species and how early they start participating in the biomineralisation processes remain unknown. The aim of the present study was twofold, that is, to identify the pioneer Cyanobacteria in hot springs (i.e. Aedipsos area, Greece) and to record their early biomineralisation processes. The in situ experimental approach included the setup of sterile glass and/or plexiglass slides in several locations to facilitate colonisation by Cyanobacteria, and removal of slides for study after 48–202 h. Synechococcales (37%) and Oscillatoriales (33%) were the dominant orders, followed by Chroococcales (15%) and Spirulinales (11%); whereas Chroococcidiopsidales (4%) was found only in a few sites. The order Nostocales was not observed at the early stages of colonisation although it was present in mature stages. Forty‐three species of Cyanobacteria were identified as pioneer microorganisms, with Spirulina subtilissima being the most frequently found. The most common pioneers were multicellular filamentous Cyanobacteria, that is, organisms with a large surface area able to form significant amounts of extracellular polymeric substances. Among the pioneers, thermophilic species of Cyanobacteria were typical such as Chroococcidiopsis thermalis, Chroococcus thermalis, Leptolyngbya thermalis, S. subtilissima and Symploca thermalis, as well as typical limestone substrate species such as Chroococcus lithophilus and Leptolyngbya laminosa. Temperature seems to affect biodiversity. Also, pioneers were found to contribute to the biomineralisation processes from their first appearance. In the studied samples, three biomineralisation processes were identified, that is, (i) calcification of cyanobacterial sheaths, (ii) trapping of carbonate crystals on a crystal retention lattice formed by extracellular polymeric substances and filaments and (iii) trapping and confinement of carbonate crystals around filamentous Cyanobacteria.

Mechanism of MnO2 nanorods toxicity in marine microalgae Chlorella sorokiniana during long-term exposure

Due to the increasing production and use of nanomaterials (NMs), their potential toxic impacts on the environment should be considered for a safe application of NMs. In this regard, the potential hazards of MnO2 nanorods (NRs) on the green microalgae Chlorella sorokiniana during long-term exposure were investigated. Exposure to the high concentration of MnO2 NRs (100 and 200 mg L−1) significantly reduced the cell number of C. sorokiniana over 20 days of the experiment. The different concentrations of MnO2 NRs (25–200 mg L−1) induced the remarkable increase in the chlorophyll (a+b) content of algal cells due to the shading effect of NRs. For more than 72 h, the chlorophyll content of microalgae decreased due to the aggregation of NRs and the possible effects of oxidative stress. Long-term exposure to high concentrations of NRs caused a significant decrease in the primary and secondary metabolites of microalgae, including carotenoids, phenolic compounds, proteins, lipids, and carbohydrates. Oxidative stress was one of the possible toxic mechanisms of MnO2 NRs to microalgae validated by an increase in lipid peroxidation induced by exposure to NRs. The algal cells increased the catalase activity and the amount of extracellular polymeric substances in response to NRs toxicity. The low level of Mn ions in the culture media indicated that MnO2 NRs dissolution was not the cause of the observed reduction in the microalgae growth. Moreover, the bulk form of MnO2 was not involved in the toxic impact of MnO2, which was documented by an insignificant decrease in the growth, pigment, and lipid peroxidation of C. sorokiniana. These results may provide an additional insight into the potential hazards of MnO2 NRs on the aquatic ecosystem.

Efficient removal of organic compounds in eutrophic water via a synergy of cyanobacterial extracellular polymeric substances and permanganate.

This study provides a new thinking for the efficient utilization of permanganate (Mn (VII)) in eutrophic water treatment. Eutrophic water contained a large amount of extracellular polymeric substances (EPS) with reduction and chelation; this study used phenol as typical organic matter and cyanobacteria EPS as a representative EPS to explore the mechanism by which EPS influences the oxidation of phenol by Mn(VII) at pH 5.0-9.0. The results showed that under the condition of pH 5.0-7.0, adding 0.2-10 mg/L EPS to the Mn(VII) system could effectively improve the oxidation efficiency of Mn(VII) for phenol. EPS promoted the continuous formation and stability of in situ EPS-MnO2 colloids and significantly enhanced the oxidation of Mn(VII). EPS also combined with phenol and increased the electron cloud density to promote the oxidation of phenol by Mn(VII).

Correlation Between the Amount of Extracellular Polymeric Substances and the Survival Rate to Freeze-Drying of Probiotics.

To demonstrate that the amount of extracellular polymeric substances (EPS) and the freeze-dried viability of probiotics are correlated. Three strains of probiotics including Lactiplantibacillus plantarum, Lactobacillus acidophilus, and Bifidobacterium bifidum were subjected to environmental challenges, such as temperature, pH, and carbon dioxide. The results indicated that the challenges could stimulate the EPS synthesis of the probiotics. The experimental correlation between the amount of synthesized EPS and the freeze-dried survival rate was also analyzed, and the viability of each of the three strains was represented by the following functions in which the equation of L. plantarum is y =-0.0336x2 + 2.7059x-14.849 with R2 = 0.9699, the B. bifidum's equation is y =-0.0554x2 + 2.6243x-13.654 with R2 = 0.9554, and the L. acidophilus's one was y = 0.0346x2 + 0.5862x-9.1339 with R2 = 0.9733. This could be a new approach to determining the freeze-dried viability of probiotic strains based on the measured EPS content.