Extracellular Polymeric Substances Formation Research Articles

Microbial Biofilm Inhibition Using Magnetic Cross-Linked Polyphenol Oxidase Aggregates.

Microbial biofilm accumulation poses a serious threat to the environment, presents significant challenges to different industries, and exhibits a large impact on public health. Since there has not been a conclusive answer found despite various efforts, the potential green and economical methods are being focused on, particularly the innovative approaches that employ biochemical agents. In the present study, we propose a bio-nanotechnological method using magnetic cross-linked polyphenol oxidase aggregates (PPO m-CLEA) for inhibition of microbial biofilm including multidrug resistant bacteria. Free PPO solution showed only 55-60% biofilm inhibition, whereas m-CLEA showed 70-75% inhibition, as confirmed through microscopic techniques. The carbohydrate and protein contents in biofilm extracellular polymeric substances (EPSs) were reduced significantly. The m-CLEA demonstrated reusability up to 5 cycles with consistent efficiency in biofilm inhibition. Computational work was also done where molecular docking of PPO with microbial proteins associated with biofilm formation was conducted, resulting in favorable binding scores and inter-residual interactions. Overall, both in vitro and in silico results suggest that PPO interferes with microbial cell attachment and EPS formation, thereby preventing biofilm colonization.

Effect of magnetic field coupled magnetic biochar on membrane bioreactor efficiency, membrane fouling mitigation and microbial communities

The excitation by magnetic field was established to mitigate the membrane fouling of magnetic biochar (MB)-supplemented membrane bioreactor (MBR) in this study. The results showed that the transmembrane pressure (TMP) increase rates decreased by about 8 % after introducing the magnetic field compared with the magnetic biochar-MBR (MB-MBR). Membrane characterization suggested that the flocs in the magnetic field-magnetic biochar-MBR (MF-MB-MBR) formed a highly permeable developed cake layer, and a fluffier and more porous deposited layer on membrane surface, which minimized fouling clogging of the membrane pores. Further mechanistic investigation revealed that the decrease in contact angle of fouled membrane surface in MF-MB-MBR, i.e. an enhanced membrane hydrophilicity, is considered important for forming highly permeable layers. Additionally, the magnetic field was demonstrated to have a positive effect on the improvement of the magneto-biological effect, the enhancement of charge neutralization and adsorption bridging between sludge and magnetic biochar, and the reduction of formation of extracellular polymeric substances (EPSs), which all yielded sludge flocs with a large pore structure conducive to form a fluffy and porous deposited layer in the membrane surface. Furthermore, high-throughput sequencing analysis revealed that the magnetic field also led to a reduction in microbial diversity, and that it promoted the enrichment of specific functional microbial communities (e.g. Bacteroidetes and Firmicutes) playing an important role in mitigating membrane fouling. Taken together, this study of magnetic field-enhanced magnetic biochar for MBR membrane fouling mitigation provides insights important new ideas for more effective and sustainable operation strategies.

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

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

Extracellular polymeric substances in electroactive biofilms play a crucial role in improving the efficiency of microbial fuel and electrolysis cells.

In microbial electrochemical cells (MECs), electroactive microbial biofilms can transmit electrons from organic molecules to anodes. To further understand the production of anodic biofilms, it is essential to investigate the composition and distribution of extracellular polymeric substance (EPS) in the MECs. In this study, the structure of EPS was examined in microbial electrolysis cells from mixed cultures forming biofilm using carbon fiber fabric anode. EPS was extracted from the anode biofilm of microbial electrolysis cells inoculated with mixed microbial culture. The anode biofilm yielded 0.4mg of EPS, of which 51.2% was humic substance, 16.2% was protein, 12.6% was carbohydrates, and 20% consisted of undetermined substances. Using epifluorescence microscopy, the composition of bacterial cells and their location inside EPS were studied, and the distribution of microbial communities was compared based on current density results in the presence of various carbohydrates. On the electrode surface, bacteria and EPS gathered or overlapped in various locations can affect microbial electrochemical performance. Our findings showed that EPS formation in electroactive biofilms would be important for enhanced efficiency of electricity- or hydrogen-producing microbial electrolysis cells.

Microbial colonization and chemically influenced selective enrichment of bacterial pathogens on polycarbonate plastic.

Plastic pollution in aquatic environments poses significant concerns due to its potential to serve as a refuge for aquatic pathogens. However, the role of plastic surfaces and microbial biofilm interfaces in facilitating pathogen development remains poorly understood. In this study, a microcosm setup was employed to investigate the interactions between plastics and the microbial community and examine the differences in bacterial community composition and potential pathogen occurrences between the plastisphere-biofilm and surrounding seawater. Community composition analysis combined with SEM observations over time indicated that biofilm extracellular polymeric substance formation over 14 days had a link with the relative abundance and succession patterns of pathogen taxa. Colony clusters were observed on biofilms from day 7 and coincided with higher bacterial pathogen dominance. On day 14, pathogen abundance overall decreased with a potentially degrading biofilm. Pseudomonas and Pseudoalteromonas were the dominant potential pathogen groups observed in the microcosm. When further subjected to chemical treatment as an imposed environmental stress over time, biofilm-associated Psuedoalteromonas sharply increased in abundance after three days of exposure, but quickly diminished by 14days in favor of genera such as Acinetobacter, Pseudomonas, and Staphylococcus. These results suggest that environmental plastisphere-biofilms can promote the early selection, enrichment, and spread of pathogenic bacteria in the aquatic environment and could be later worsened under chemical and long-term pressure. This study provided new insights into the succession of pathogens in plastisphere biofilms, contributing to the understanding of pathogen risks involved in emerging plastisphere biofilms in light of global plastic pollution.

Physiological Performance and Biosorption Capacity of Exiguobacterium sp. SH31 Isolated from Poly-Extreme Salar de Huasco in the Chilean Altiplano: A Study on Rare-Earth Element Tolerance

Rare-earth elements (REEs) are crucial metals with limited global availability due to their indispensable role in various high-tech industries. As the demand for rare-earth elements continues to rise, there is a pressing need to develop sustainable methods for their recovery from secondary sources. Focusing on Exiguobacterium sp. SH31, this research investigates the impact of La, Eu, Gd, and Sm on its physiological performance and biosorption capacity. Tolerance was assessed at pHpzc from 7 to 8 with up to 1 mM rare-earth element concentrations. This study visualized the production of extracellular polymeric substances using Congo red assays and quantified them with ultraviolet–visible spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy characterized the functional groups involved in metal interactions. The SH31 strain displayed significant rare-earth element tolerance, confirmed extracellular polymeric substance (EPS) production under all conditions, and increased production in the presence of Sm. Spectroscopy analysis revealed changes in wavelengths associated with OH and R-COO-, suggesting rare-earth element interactions. SH31 demonstrated efficient metal adsorption, with removal rates exceeding 75% at pHpzc 7 and over 95% at pHpzc 7.5 and 8. The calculated Qmax value for rare-earth element biosorption was approximately 23 mg/g, and Langmuir isotherm models effectively described metal sorption equilibria. Genomic exploration identified genes related to extracellular polymeric substance formation, providing insights into underlying mechanisms. This study presents the first evidence of efficient La, Eu, Gd, and Sm adsorption by SH31, emphasizing its potential significance in rare-earth element recovery.

Formation of extracellular polymeric substances corona on TiO2 nanoparticles: Roles of crystalline phase and exposed facets

Nanoparticles (NPs) in the environment can interact with macromolecules in the surrounding environment to form eco-corona on their surfaces, which in turn affects the environmental fate and toxicity of nanoparticles. Wastewater treatment plants containing large amounts of microbial extracellular polymeric substances (EPS) are an important source of NPs into the environment, where the formation of EPS coronas on NPs is critical. However, it remains unclear how the crystalline phase and exposed facets, which are intrinsic properties of NPs, affect the formation of EPS coronas on NPs. This study investigated the formation of EPS corona on three TiO2 NPs (representing the most widely used engineered NPs) with different crystalline phases and exposed facets. The protein type and abundance in EPS coronas on TiO2 NPs varied depending on the crystalline phase and exposed facets. Anatase with {101} facets and {001} facets preferred to adsorb proteins with lower molecular weights and higher H-bonding relevant amino acids, respectively, while EPS corona on rutile with {110} facets had proteins with higher hydrophobicity. In addition, the selective adsorption of proteins was primarily determined by steric hindrance, hydrogen bonding, and hydrophobic interaction between TiO2 NPs and proteins, which were affected by changes in aggregation state, surface hydroxyl density, and hydrophobicity of TiO2 NPs induced by crystalline phase and exposed facets. Moreover, crystalline phase and exposed facets-induced EPS corona changes altered the aggregation state and oxidation potential of TiO2–EPS corona complexes. These findings emphasize the important role of crystalline phase and exposed facets in the environmental behavior of nanoparticles and may provide insights into the safe design of nanoparticles.

Insights into the interaction between mineral formation and heavy metals immobilization, mediated by Virgibacillus exopolymeric substances

Heavy metal pollution poses significant risks to both the environment and human health due to their toxicity, long residence times, and their ability to bioaccumulate and bio magnify across the food chain. To address this issue, microbial biomineralization has emerged as a promising approach to the bio-removal of heavy metals through immobilization. This process is facilitated by extracellular polymeric substances (EPS), which also play a crucial role in mediating mineral formation. In this study, the interactions between several selected heavy metals (Cd2+, Cu2+, Ni2+, Zn2+), EPS, and mineral formation were investigated using two mineral-forming Virgibacillus strains isolated from the Qatari sabkhas, which are known to be suitable sites for the formation of biominerals. An additional non-mineral-forming Virgibacillus strain isolated from the Dukhan oil waste dumpsite was also investigated. Cd2+ and Zn2+ were to inhibit mineral formation, likely due to competition with Ca2+ and Mg2+ ions during biomineralization. However, exposure to Ni2+ or Cu2+ resulted in changes in the FTIR spectra of the EPS, suggesting the presence of specific functional group bindings within the EPS matrix. The EPS produced by each strain was also directly associated with their efficiency (%) at removing heavy metals. Notably, the EPS from Virgibacillus halodenitrificans Z4D1, the non-mineral-forming strain, exhibited the highest heavy metal removal efficiency of 31.7 % for Zn2+. These findings reveal that EPS do not only affect the biomineralization process but also that the functional groups in EPS have a direct effect on the immobilization of several heavy metals. Conditions that are not suitable for mineral formation may instead be appropriate for the removal of specific heavy metals.

Shumkonia mesophila gen. nov., sp. nov., a novel representative of Shumkoniaceae fam. nov. and its potentials for extracellular polymeric substances formation and sulfur metabolism revealed by genomic analysis.

A microaerophilic, mesophilic, chemoorganoheterotrophic bacterium, designated Y-P2T, was isolated from oil sludge enrichment in China. Cells of the strain were Gram-stain-negative, non-motile, non-spore-forming, rod-shaped or slightly curved with 0.8-3.0µm in length and 0.4-0.6µm in diameter. The strain Y-P2T grew optimally at 25°C (range from 15 to 30°C) and pH 7.0 (range from pH 6.0 to 7.5) without NaCl. The major cellular fatty acids were C16:0, summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), summed feature 8 (C18:1 ω7c and/or C18:1 ω6c). The main polar liquids of strain Y-P2T comprised phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). The respiratory quinone was Q-10. Acetate and H2 were the fermentation products of glucose. The DNA G + C content was 66.0%. Strain Y-P2T shared the highest 16S rRNA gene sequence similarity (90.3-90.6%) with species within Oceanibaculum of family Thalassobaculaceae in Rhodospirillales. Phylogenetic analyses based on 16S rRNA gene sequences and genomes showed that strain Y-P2T formed a distinct evolutionary lineage within the order Rhodospirillales. On the basis of phenotypic, phylogenetic and phylogenomic data, we propose that strain Y-P2T represents a novel species in a novel genus, for which Shumkonia mesophila gen. nov., sp. nov., within a new family Shumkoniaceae fam. nov. The type strain is Y-P2T (= CCAM 826T = JCM 34766T).

Sucrose-mediated formation and adhesion strength of Streptococcus mutans biofilms on titanium

Biofilms consist of bacterial cells surrounded by a matrix of extracellular polymeric substance (EPS), which protects the colony from many countermeasures, including antibiotic treatments. Growth and formation of bacterial biofilms are affected by nutrients available in the environment. In the oral cavity, the presence of sucrose affects the growth of Streptococcus mutans that produce acids that erode enamel and form dental caries. Biofilm formation on dental implants commonly leads to severe infections and can restrict osseointegration necessary for the implant to be successful. This work determines the effect of sucrose concentration on biofilm EPS formation and adhesion of Streptococcus mutans, a common oral colonizer, to titanium substrates simulating common dental implants. Biofilm formation and profiles are visualized at high magnification with scanning electron microscopy (SEM). Large mounds and complex structures consisting of bacterial cells and EPS can be seen in biofilms at sucrose concentrations that are favorable for biofilm growth. The laser spallation technique is used to apply stress wave loading to the biofilm, causing the biofilm to delaminate at a critical tensile stress threshold. The critical tensile stress threshold is the adhesion strength. Because laser spallation applies the stress loading to the rear of the substrate, bulk adhesion properties of the biofilm can be determined despite the heterogenous composition and low cohesion strength of the biofilm. Statistical analysis reveals that adhesion strength of biofilms initially increase with increasing sucrose concentration and then decrease as sucrose concentration continues to increase. The adhesion strength of bacterial biofilms to the substrate in this study is compared to the adhesion of osteoblast-like cells to the same substrates published previously. When sucrose is present in the biofilm growth environment, S. mutans adhesion is higher than that of the osteoblast-like cells. Results of this study suggest sucrose-mediated S. mutans biofilms may outcompete osteoblasts in terms of adhesion during osseointegration, which could explain higher rates of peri-implant disease associated with high sugar diets. Further studies demonstrating adhesion differentials between biofilms and cells including co-cultures are needed and motivated by the present work.

Organic carbon source excites extracellular polymeric substances to boost Fe0-mediated autotrophic denitrification in mixotrophic system

Fe0-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe0 corrosion. The mixotrophic denitrification (MDN) coupling Fe0-mediated ADN with heterotrophic denitrification (HDN) can circumvent the weakening of Fe0-mediated ADN over operation time. But the interaction between HDN and Fe0-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO3−-N ratio increased from 0.0 to 1.8–2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe0-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO3−-N removal significantly, while accelerated the electron release originating from Fe0 corrosion. The bioorganic-Fe complexes were generated on Fe0 surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe0-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe0-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.

Starvation combined with constant anode potential triggers intracellular electron storage in electro-active biofilms

The accumulation of electrons in the form of Extracellular Polymeric Substances (EPS) and poly-hydroxyalkanoates (PHA) has been studied in anaerobic processes by adjusting the access of microorganisms to the electron donor and final electron acceptor. In Bio-electrochemical systems (BESs), intermittent anode potential regimes have also recently been used to study electron storage in anodic electro-active biofilms (EABfs), but the effect of electron donor feeding mode on electron storage has not been explored. Therefore, in this study, the accumulation of electrons in the form of EPS and PHA was studied as a function of the operating conditions. EABfs were grown under both constant and intermittent anode potential regimes and fed with acetate (electron donor) continuously or in batch. Confocal Laser Scanning Microscopy (CLSM) and Fourier-Transform Infrared Spectroscopy (FTIR) were used to assess electron storage. The range of Coulombic efficiencies, from 25 to 82%, and the biomass yields, between 10 and 20%, indicate that storage could have been an alternative electron consuming process. From image processing, a 0.92 pixel ratio of poly-hydroxybutyrate (PHB) and amount of cells was found in the batch fed EABf grown under a constant anode potential. This storage was linked to the presence of living Geobacter and shows that energy gain and carbon source starvation were the triggers for intracellular electron storage. The highest EPS content (extracellular storage) was observed in the continuously fed EABf under an intermittent anode potential, showing that constant access to electron donor and intermittent access to the electron acceptor leads to the formation of EPS from the excess energy gained. Tailoring operating conditions can thus steer the microbial community and result in a trained EABf to perform a desired biological conversion, which can be beneficial for a more efficient and optimized BES.

Combinatory effects of microplastics and emerging contaminants on alga Chlamydomonas reinhardtii

In oceans today, there is much concern about the effects of microplastics (MPs) and other emerging contaminants (ECs). Here, the authors investigated the combinatory effects of the MPs poly(vinyl chloride) (PVC) and acrylates/C10–30 alkyl acrylates cross-polymer (AC) (which are commonly found in face wash), together with 2-phenoxyethanol (an EC commonly used in soaps). The model photosynthetic unicellular alga Chlamydomonas reinhardtii was used to study the potential of these pollutants to initiate algal blooms. It was shown that AC alone resulted in a greater decline in algal biomass as compared with PVC in the short term (14 days). While algal cultures exposed to PVC registered the highest increase in concentrations of the chlorophyll a pigment, it was the combinatory effects of each MP and 2-phenoxyethanol that were the most pronounced in terms of the large increase in algal biomass and the formation of extracellular polymeric substances. Proliferative growths of C. reinhardtii after prolonged exposure to AC–EC contaminants show potential for initiating algal blooms in aquatic environments. Hence, AC should be considered for regulation of waste water removal into water bodies, and other combinations of MPs and ECs should also be investigated.

Base type determines the effects of nucleoside monophosphates on microalgae–bacteria symbiotic systems

Microalgae are promising sources of clean energy. Bioflocculation by cocultured bacteria is an effective way to harvest microalgae. As a key foundation for microorganisms, phosphorus is theoretically effective in shaping microalgae production and flocculation. In this study, the impacts of 23 nucleoside monophosphates on Auxenochlorella pyrenoidosa growth, lipid synthesis, and self-settlement and on the symbiotic bacterial system were investigated. Adenosine monophosphate was the most effective in enhancing microalgae development (2.14–3.16 × 108 cells/mL) and lipid production (average 10.48%) and resulted in a low settling velocity. Samples were divided into two groups, purine and pyrimidine feeding, according to a random forest analysis (OOB = 0%, p < 0.001). Purine feeding resulted in the highest soluble extracellular protein and polysaccharide secretion (p < 0.01). KEGG ortholog count prediction of functional genes related to biofilm formation was conducted using PICRUSt2, and significant upregulation (FC ≥ 1.77, p < 0.05) of the extracellular polymeric substance formation functional group was observed in the adenosine and guanosine treatments. The symbiotic bacterial community structure differed substantially between purine- and pyrimidine-feeding systems. In summary, these results indicated that the effect of nucleoside monophosphates on the microalgae–bacteria system is determined by the base type (purine or pyrimidine) rather than the molecular structure (cyclic or noncyclic).

Exploring interactions between quorum sensing communication and microbial development in anammox membrane bioreactor

The long duration required to enrich bacteria that perform anaerobic ammonium oxidation (anammox) limits their wide application in wastewater treatments. Anammox enrichment requires extensive microbial development, but the mechanisms involved are still being studied. Here, a total nitrogen removal rate of 1.22 kg N/m3/day was obtained over 280 days when anammox was enriched in a membrane bioreactor (MBR). Interactions between quorum sensing (QS) and microbial community development were investigated. Acyl-homoserine lactones (AHLs) were detected in the MBR effluent, with C8-HSL having the highest concentration (2.05 ng/L). The specific anammox activity (SAA) of the biomass increased from 335.8 (± 16.4) mg NH4+-N/g VSS/day to 382.9 (± 19.6) mg NH4+-N/g VSS/day with 0.1 μM C8-HSL addition. Anammox bacteria from the genus Candidatus Brocadia were enriched in the MBR. Metagenomic analysis suggested quorum sensing dependent on AHL and c-di-GMP (bis-[3′−5′]-cyclic dimeric guanosine monophosphate) contributed to microbial development. C-di-GMP-dependent quorum sensing may impact the formation of extracellular polymeric substances (EPS) and cell motility of biomass.

Different dissolved oxygen levels drive polyhydroxyalkanoate biosynthesis from hydrolyzed polyacrylamide-containing oil sludge

Hydrolyzed polyacrylamide (HPAM)-containing oil sludge is an available resource for the generation of polyhydroxyalkanoates (PHAs) by native functional microorganisms in the sludge. The impact of dissolved oxygen (DO) as an important factor on these processes is now unclear. Thus, this study established the biosystems involving the full range of DO levels involving anaerobic, anoxic and aerobic conditions by using HPAM-containing oil sludge as both substrates and microorganisms. PHAs, intermediate metabolites, extracellular polymeric substances (EPS) and microbial communities in these biosystems were determined. The associations between different PHAs and metabolites, and EPS, and functional microorganisms were explored. The PHAs produced in these biosystems included poly(3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate) (P(3HO-co-3HD-co-3HDD)), poly(3-hydroxydecanoate) (P(3HD)), poly(3-hydroxyoctanoate) (P(3HO)), poly(3-hydroxyvalerate) (P(3HV)) and poly(3-hydroxybutyrate) (P(3HB)). The yield of medium-chain-length (mcl)-PHAs first increased and then remained stable with DO level (0–3.5 mg·L−1). While the yield of short-chain-length (scl)-PHAs first rose and then descended and finally kept steady with DO level. Different PHA production was correlated with volatile fatty acid (VFA) generation, EPS formation and microbial function. The change trend of VFA yield was coincided with that of scl-PHA building blocks. Polysaccharides and tyrosine/tryptophan proteins in EPS were closely related to mcl-PHA biosynthesis. Pseudomonas, Bacillus, Thauera, Aeromonas and Azoarcus as the shared multifunctional bacteria dominated the biosynthesis of mcl- and scl-PHAs. Different DO levels regulated VFA generation, EPS formation and microbial function of HPAM-containing oil sludge, and consequently drove the biosynthesis of different PHAs. This study is expected to achieve a “win-win” for the environmentally friendly treatment and the resource recovery of HPAM-containing oil sludge.

Biochar facilitates ferrihydrite reduction by Shewanella oneidensis MR-1 through stimulating the secretion of extracellular polymeric substances

Biochar can mediate extracellular electron transfer (EET) of Shewanella oneidensis MR-1 and subsequently facilitate dissimilatory reduction of iron(III) minerals. Previous studies mainly focused on the interaction of biochar and membrane cytochrome complexes to reveal the mediating mechanisms between biochar and S. oneidensis MR-1. However, the influence of biochar on the production and activity of extracellular polymeric substances (EPS) has long been neglected, despite the fact that EPS are commonly exudated by S. oneidensis MR-1 and can participate in a variety of electron transfer processes due to their redox activity. Here, we performed a series of microbial ferrihydrite reduction experiments in combination with electrochemical voltametric and impedance analyses to investigate the role of biochar in the formation and transformation of cell EPS during EET. Results showed that the added biochar not only functioned as an electron shuttle facilitating electron transfer, but also induced the secretion of five times more EPS by S. oneidensis MR-1, leading to a 1.4-fold faster ferrihydrite reduction in comparison with biochar-free setups. We further extracted the secreted EPS and found that the proportion of redox-active exoproteins was significantly (p < 0.05) increased in the EPS and resulted in a higher electron exchange capacity in secreted EPS. Such increased exoprotein content also induced a higher ratio of exoprotein to exopolysaccharide, which largely dropped diffusion and electron transfer impedance of EPS to 1.1 and 18 Ω, respectively, and accelerated the EET and thus the ferrihydrite reduction. Overall, our findings revealed the interactions between biochar and EPS matrices, which could potentially play a critical role in EET processes in both environmental or biotechnological systems.

Experimental investigation of the performance of anaerobic membrane bioreactor with electrolytic regeneration (AMBER) for challenges and options in wastewater treatment

Significant changes in wastewater services are necessary for achieving the sustainable development goals (SDGs), by utilizing resource recovery, recycle, and reuse in urban wastewater-treatment plants. Based on recent experiences, to improve the filtration behavior of a membrane bioreactor, a hybrid system including an upgraded anaerobic baffled reactor coupled with an electrolysis process and a nanocomposite-membrane was developed. The system, called an anaerobic membrane bioreactor with electrolytic regeneration (AMBER), is a bio-electrochemical process that is expected to be simultaneously efficient in both biogas augmentation and fouling mitigation. The goals were to enhance the stability and efficiency of the anaerobic membrane bioreactor. The integration of the electrolytic process with the ABR (EABR) using a pair of iron electrodes enhanced the removal of contaminants in the ABR while successfully maintained pH in the optimum range for anaerobic digestion (6.8 to 7.2). Then, the performance of AMBER in pollutant removal, including organic load, suspended solids, and microbial load, were investigated over 240 days. The results showed that configuration considerably enhanced permeate flux, as it reduced the deposition of extracellular polymeric substances (EPS) on the surface of the nanocomposite membrane, leading to a reduction in membrane fouling. EPS was extracted and quantified to compare the effect of biogas backwash on the function of the membrane reactor. After 7 d of operation with a daily biogas backwash, the flux reduction was approximately 13 % for the conventional combination of the anaerobic baffled reactor and the membrane bioreactor (AMBR), while it was limited to 4 % in AMBER. After cleaning by the biogas, EPS formation decreased 63 % in AMBER when compared to the AMBR. The results revealed that AMBER can be considered an environmentally competitive bioenergy technology for wastewater treatment with the purpose of water recovery and reuse, employing optimized operational conditions, application of antifouling membranes, and electrically-based strategies.

Antibiofilm Activity of the Methanolic Extract of Nutmeg Oil against Bacillus subtilis

Biofilm is formed by one or different types of microbes that can grow on different surfaces. Bacteria, fungi, and many protists can form biofilms. Biofilm formation requires cell to cell signaling mechanism which is defined as quorum sensing. In this work, we have studied about the antibiofilm activity of methanolic extract of nutmeg against Gram-positive Bacillus subtilis bacteria. Our test extract inhibited biofilm production as well as eradication of pre-formed biofilm in B. subtilis. Extracellular polymeric substance (EPS) is the biopolymer of microbial origin in which biofilm producing microbes are embedded. When test extract was treated with organisms producing biofilms it can also reduce the production of EPS of biofilm. All the quantitative analysis of this work concludes that methanolic extract of Myristica fragrans seed extract inhibited biofilm formation by 47%, eradicated the pre-formed biofilm by 28.5%, and inhibited EPS formation by 60%. All these quantitative tests were confirmed by microscopic analysis. All Our study concludes that M. fragrans seed extract can inhibit biofilm formation and can destruct preformed biofilm in Gram-positive bacteria.

Optimization of Microalgae–Bacteria Consortium in the Treatment of Paper Pulp Wastewater

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.