In vascular plants, the root endodermis surrounds the central vasculature as a protective sheath that is analogous to the polarized epithelium in animals, and contains ring-shaped Casparian strips ...that restrict diffusion. After an initial lag phase, individual endodermal cells suberize in an apparently random fashion to produce 'patchy' suberization that eventually generates a zone of continuous suberin deposition. Casparian strips and suberin lamellae affect paracellular and transcellular transport, respectively. Most angiosperms maintain some isolated cells in an unsuberized state as so-called 'passage cells', which have previously been suggested to enable uptake across an otherwise-impermeable endodermal barrier. Here we demonstrate that these passage cells are late emanations of a meristematic patterning process that reads out the underlying non-radial symmetry of the vasculature. This process is mediated by the non-cell-autonomous repression of cytokinin signalling in the root meristem, and leads to distinct phloem- and xylem-pole-associated endodermal cells. The latter cells can resist abscisic acid-dependent suberization to produce passage cells. Our data further demonstrate that, during meristematic patterning, xylem-pole-associated endodermal cells can dynamically alter passage-cell numbers in response to nutrient status, and that passage cells express transporters and locally affect the expression of transporters in adjacent cortical cells.
Extracellular polymeric substances (EPS) with high molecular weights, secreted from microorganisms, play a critical functional role in the aerobic granular sludge (AGS). To investigate the level and ...function of EPS during the granulation of aerobic sludge and in the mature AGS, a sequencing batch reactor (SBR) was operated for 70 days. Aerobic granules with an average diameter of 0.25 mm were obtained with reducing settling time of sludge. Simultaneous removals of COD, nitrogen and phosphorus by the mature AGS exceeded 90, 95 and 95%, respectively. The EPS content increased significantly to above 333 mg/g MLVSS during the initial stage, and after that, it stabilized at about 240 mg/g MLVSS as the mature AGS formed, higher than that of the seed sludge (212 mg/g MLVSS). The increased EPS contents showed a negative correlation with SVI values, while a strong positive relationship with the formation of the AGS. The protein/polysaccharide (PN/PS) ratio in the EPS increased from 1.42 to 4.17, and TP/MLSS increased to about 6%, with the formation of AGS. The proportion of extracellular-P increased with the increase of EPS, and then maintained stable at about 20%, indicating EPS promoted the removal of phosphorus. Furthermore, the results from the Standards, Measurements and Testing (SMT) and X-Ray Diffraction (XRD) showed that phosphorus in the AGS mainly existed in the form of inorganic phosphorus (IP) and the proportion of Ca5(PO4)3(OH) in IP was up to 92%. This investigation demonstrated that EPS had a positive relationship with the sludge granulation and nutrients removal.
•Increased EPS content is conducive to aerobic sludge granulation formation.•Protein is the predominant composition in EPS contributed to sludge granulation.•The increased EPS promote the phosphorus removal of AGS.•Phosphorus in the AGS mainly exists in the form of inorganic phosphorus.
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•Biosynthesis of various PHAs from sludge for different carbon source concentrations.•Correlations among PHAs, EPS and sludge features were evaluated for the first time.•Both EPS and ...sludge characteristics showed similar trends for each carbon source.•Positive correlations were found between MLSS/polysaccharides and PHAs.•Sludge floc size showed significant negative correlation with PHAs.
To understand PHAs accumulation process well in the stand point of the sludge characteristics, polyhydroxyalkanoates (PHAs) accumulation by activated sludge was investigated in correlation with sludge properties, such as particle size, mixed liquor suspended solids (MLSS) and extracellular polymeric substances (EPS) under different carbon sources (e.g., acetate, propionate and mixed carbons) at 2, 4, 6 and 8 g/L. The efficiency of PHAs synthesis from sludge with sodium acetate as carbon source was superior to that with sodium propionate as carbon source and mixed carbon sources in the sequencing biological reactors, while EPS and sludge characteristics showed similar trends for each carbon source. Various carbon sources did not induce significant differences in the correlations. Polyhydroxybutyrate (PHB) showed good correlation with MLSS (R = 0.782) and sludge floc size (R = −0.58). In the reactors with carbon sources of propionate and mixed carbons, polyhydroxyvalerate (PHV) and PHBV correlated with MLSS (R = 0.480 and 0.489, respectively), sludge floc size (R = −0.921 and −0.666, respectively) and concentrations of polysaccharides (R = 0.726, 0.557, respectively). According to the correlations, improving the concentration of sludge, promoting the production of extracellular polymeric substances (EPS) and decreasing the sludge floc size were supposed to be effective approaches for further accumulation of the PHAs. This study is the first to systematically establish the correlations among EPS, characteristics of activated sludge and PHAs accumulation, can provide a theoretical foundation for the engineering design and the operational parameters selection of PHAs production by activated sludge.
This paper describes a unique molecular mechanism for the EPS-mediated synthesis of CdS QDs by sulfate-reducing bacteria (SRB) under carbon source-induced reinforcement. Under the induced by carbon ...sources (HCOONa, CH3COONa and C6H12O6), there was a significant increase in EPS production of SRB, particularly in protein, and the capacity of Cd(II) adsorption was further enhanced. CdS QDs were extracellularly synthesized by adding S2- after Cd(II) adsorption. The results showed that CdS QDs were wrapped or adhered by EPS, and the most significant increase in Arg and Lys among basic amino acids in EPS after HCOONa-induced was 133.34% and 63.89%, respectively. This may serve as a biological template for QD synthesis, producing protein gels with a large number of microcavities and controlling the nucleation of CdS QDs. The highest yield of HCOONa-CdS was achieved after induction, with 23.59 g/g biomass per unit strain, which was 447.34% higher than that before induction and was at a high level in previous studies. The synthesized CdS QDs were uniform in size distribution and had higher luminescence activity and a larger specific surface area than those synthesized by the chemical synthesis route, provides a new idea for EPS treatment of heavy metal wastewater and metal biorecovery.
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•The yield and heavy metal adsorption capacity of EPS were significantly improved after SRB was induced by carbon source.•The yield of CdS QDs increases with the reinforcement of EPS performance.•The basic amino acids Arg and Lys control the nucleation of CdS QDs.•EPS can adjust the PL fluorescence properties and specific surface area of CdS QDs.
Overwhelming growth of bacterial biofilms on different metal-based pipeline materials are intractable and pose a serious threat to public health when tap water flows though these pipelines. Indeed, ...the underlying mechanism of biofilm growth on the surface of different pipeline materials deserves detailed exploration to provide subsequent implementation strategies for biofilm control. Thus, in this study, how bacteria response to their encounters was explored, when they inhabit different metal-based pipeline substrates. Results revealed that bacteria proliferated when they grew on stainless steel (SS) and titanium sheet (Ti), quickly developing into bacterial biofilms. In contrast, the abundance of bacteria on copper (Cu) and nickel foam (Ni) substates decreased sharply by 4–5 logs within 24 h. The morphological shrinkage and shortening of bacterial cells, as well as a sudden 64-fold increase of carbohydrate content in extracellular polymeric substances (EPS), were observed on Cu substrate. Furthermore, generation of reactive oxygen species and fluctuation of enzymatic activity demonstrated the destruction of redox equilibrium in bacteria. Bacteria cultured on Cu substrate showed the strongest response, followed by Ni, SS and Ti. The oxidative stress increased quickly during the growth of bacterial biofilm, and almost all tested metal transporter-related genes were upregulated by 2–11 folds on Cu, which were higher than on other substrates (1–2 folds for SS and Ti, 2–9 folds for Ni). Finally, these behaviors were compared under the biofilm regulatory molecular network. This work may facilitate better understanding different response mechanisms during bacterial biofilm colonization on metal-based pipelines and provide implications for subsequent biofilm control.
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•Bacteria activity drops sharply on Cu and Ni, as compared on SS and Ti substrates.•Bacteria can adapt to SS and Ti easily to form biofilms.•Only survived bacteria can develop biofilms onto Cu and Ni substrates.•Bacteria grown onto Cu substrate have the most drastic defense activity.•All behaviors of biofilm bacteria are performed under the molecular regulatory network.
The adaptability of soil microbial communities to prolonged periods of drought is influenced by their ability to produce extracellular polymeric substances (EPS) with sufficient water retention ...properties. Microbial EPS have been extensively investigated as water reservoirs during drought, but it remains unknown how carbon substrate accessibility to soil microbial communities will affect the chemical properties of the EPS they generate, and whether this in turn will alter their water retention characteristics. In this work, we observed that the accessibility of carbon substrates influenced microbial community structure and, consequently, the chemical properties of EPS produced by the microbial communities. Our results demonstrated that an insoluble carbon substrate (i.e., chitin), stimulated microbial communities to produce EPS with measurably better water retention properties in emulated soil microenvironments in comparison to a soluble carbon substrate (i.e., N-acetylglucosamine; NAG). In all, this study demonstrates the importance of carbon substrate accessibility by soil microorganisms in regulating the community structure and consequently, the EPS carbon chemistry, which in turn can greatly influence the adaptability of soil microbial communities to drought.
•Carbon substrate accessibility regulates microbial community membership.•The properties of microbial community-produced EPS can be influenced by membership.•Soil microbial community membership influence EPS water retention properties.•Specific carbon substrates may affect microbial community EPS production and properties.
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•Rapid start-up of A/O/A-SNDPR was achieved within 15 days.•With significant in situ sludge reduction, Yobs was as low as 0.017 g MLSS/g COD.•Under the condition of long SRT without ...sludge discharge, the removal rate of TP reached 96.37%.•Candidatus_Competibacter was enriched up to 29.06 % in the system.
An anaerobic/aerobic/anoxic mode simultaneous nitrification, denitrification, and phosphorus removal system was visited for enhanced low-strength wastewater treatment and dramatic in situ sludge reduction. Results showed that rapid start-up was achieved with conventional activated sludge after 15 days, with effluent ammonia nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand being 0.25, 7.89, 0.12, 24.37 mg/L, respectively. A two-stage biomass growth rate was observed with the sludge yield of 0.285 (day 1–50) and 0.017 g MLSS/g COD (day 51–110) without sludge discharge. Dynamics of bacterial community has been identified with outstanding accumulation of Candidatus_Competibacter up to 29.06 %, which contributed to both simultaneous nutrients removal and sludge reduction. Further analysis via PICRUSt2 revealed the main pathway of nitrogen metabolism, while proposed mechanism for phosphorus removal with no sludge discharge was analyzed from the intracellular and extracellular perspectives. Overall, this study provided guidance and reference for the development and application of A/O/A-SNDPR technology.
This study investigated the influence of nitrate on aerobic granular sludge (AGS) granulation. The introduction of nitrate at 5, 15 and 20 mg L−1 promoted AGS granulation, and the promoting effect ...was positively correlated with nitrate concentrations. Meanwhile, exogenous nitrate significantly increased denitrification rate in the AGS system. However, granular disintegration appeared at a long-term addition of nitrate. An in-deep analysis showed that nitrate stimulated the secretion of extracellular polymeric substances (EPS), especially the content of proteins, which might be the main reason for the AGS granulation. However, the rapid and excessive increase in EPS might cause granular disintegration, as excessive EPS blocked the transmission of substrates, leading to the increase of dead cells in the granules. Besides, nitrate also altered the hydrophobicity of EPS and the content of α-helix, 3-turned helix and polymeric chain that favored aggregation, which also affected AGS granulation. From the microbial community level, nitrate induced the enrichment of denitrifying bacteria, including those that also functioned as EPS producers, such as Micropruina and Flavobacterium, resulting in the rapid increase of functional enzymes associated with amino acid synthesis, thereby promoting the secretion of proteins in EPS. Conversely, disintegration caused by mass transfer blockage might lead to the loss of EPS producing bacteria and subsequent decrease in EPS content, further accelerating granular disintegration.
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•AGS granulation was improved with the increase of nitrate from 5 to 20 mg L−1.•Granule disintegration appeared under a long-term effect of 5–20 mg L−1 nitrate.•The increase in nitrate promoted EPS, but excessive EPS might lead to disintegration.•Nitrate altered the hydrophobicity and the content of proteins secondary structures.•Nitrate stimulated denitrifiers with EPS producing ability.
Harmful chemicals present in electric vehicle Li-ion batteries (EV LIBs) can limit the pulp density of bioleaching processes using Acidithiobacillus sp. to 1.0% (w/v) or lower. The strong enhancing ...mechanisms of extracellular polymeric substances (EPS) on the bioleaching of metals from spent EV LIBs at high pulp density (4% w/v) were studied using bio-chemical, spectroscopic, surface structure imaging and bioleaching kinetic methods. Results demonstrated that the added EPS significantly improved bioleaching efficiency of Ni, Co and Mn improved by 42%, 40% and 44%, respectively. EPS addition boosted the growth of cells under adverse conditions to produce more biogenic H+ while Fe3+ and Fe2+ were adsorbed by the biopolymer. This increased Li extraction by acid dissolution and concentrated the Fe3+/Fe2+ cycle via non-contact mechanisms for the subsequent contact bioleaching of Ni, CO and Mn at the EV LIB-bacteria interface. During the leaching process, added EPS improved adhesion of the bacterial cells to the EV LIBs, and the resultant strong interfacial reactions promoted bioleaching of the target metals. Hence, a combination of non-contact and contact mechanisms initiated by the addition of EPS enhanced the bioleaching of spent EV LIBs at high pulp density.
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•Added EPS greatly improve bioleaching yield of spent EV LIBs at pulp density of 4%.•Added EPS boost resistance of cell to toxic chemical to produce more H+ and Fe3+/Fe2+.•Added EPS enhance cell adhesion and oxidation.•EPS increased the interface reaction in favor of leaching.•There is a significant positive correlation between the dissolution efficiency of metals and the concentration of EPS.
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