Insights into the role of extracellular DNA in heavy metal adsorption

A review of distribution and functions of extracellular DNA in the environment and wastewater treatment systems

Extracellular DNA refers to DNA fragments existing outside the cell, originating from various cell release mechanisms, including active secretion, cell lysis, and phage-mediated processes. Extracellular DNA serves as a vital environmental biomarker, playing crucial ecological and environmental roles in water bodies. This review is summarized the mechanisms of extracellular DNA release, including pathways involving cell lysis, extracellular vesicles, and type IV secretion systems. Then, the extraction and detection methods of extracellular DNA from water, soil, and biofilm are described and analyzed. Finally, we emphasize the role of extracellular DNA in microbial community systems, including its significant contributions to biofilm formation, biodiversity through horizontal gene transfer, and electron transfer processes. This review offers a comprehensive insight into the sources, distribution, functions, and impacts of extracellular DNA within aquatic environments, aiming to foster further exploration and understanding of extracellular DNA dynamics in aquatic environments as well as other environments.

Heavy metal ions interactions with G-quadruplex-prone DNA sequences

The industrial world exposes living organisms to a variety of metal pollutants. Here we investigated whether such elements affect G-rich sequences susceptible to fold into G-quadruplex (GQ) structures. Thermal stability and conformation of these oligoncleotides was studied at various molar ratios of a variety of heavy metal salts using thermal FRET, transition-FRET (t-FRET) and circular dichroism. Metal ions affected the thermal stability of the GQs to different extents; some metals had no effect on Tm while other metals caused small to moderate changes in Tm at 1:1 or 1:10 molar ratio. While most of the metals had no major effect, Al3+, Cd2+, Pb2+, Hg2+ and Zn2+ altered the thermal stability and structural features of the GQs. Some metals such as Pb2+ and Hg2+ exhibit differential interactions with telomere, c-myc and c-kit GQs. Overall, toxic heavy metals affect G-quadruplex stability in a sequence and topology dependent manner. This study provides new insight into how heavy metal exposure may affect gene expression and cellular responses.

Advances, challenges, and prospects in microalgal-bacterial symbiosis system treating heavy metal wastewater

Heavy metal (HM) pollution, particularly in its ionic form in water bodies, is a chronic issue threatening environmental security and human health. The microalgal-bacterial symbiosis (MABS) system, as the basis of water ecosystems, has the potential to treat HM wastewater in a sustainable manner, with the advantages of environmental friendliness and carbon sequestration. However, the differences between laboratory studies and engineering practices, including the complexity of pollutant compositions and extreme environmental conditions, limit the applications of the MABS system. Additionally, the biomass from the MABS system containing HMs requires further disposal or recycling. This review summarized the recent advances of the MABS system treating HM wastewater, including key mechanisms, influence factors related to HM removal, and the tolerance threshold values of the MABS system to HM toxicity. Furthermore, the challenges and prospects of the MABS system in treating actual HM wastewater are analyzed and discussed, and suggestions for biochar preparation from the MABS biomass containing HMs are provided. This review provides a reference point for the MABS system treating HM wastewater and the corresponding challenges faced by future engineering practices.

Biosorption of U(VI) and mechanisms by live and dead cells of Sphingopyxis sp. YF1

Heavy metal pollution seriously threatens the environment and human health. The biosorption of heavy metals has attracted worldwide attention due to its cost-effectiveness and environmental friendliness. It is significant to develop biosorbents with excellent adsorption performance. Sphingopyxis is widely used in the removal of various organic pollutants, but its potential application in heavy metal adsorption has been largely overlooked. This study investigates the biosorption of U(VI) onto live and dead cells of a Sphingopyxis strain YF1. The effects of pH, contact time and initial ion concentration on U(VI) adsorption investigated, and kinetic and isothermal models were used to fit the adsorption results. The results show that under pH 3-6, the adsorption of U(VI) by YF1 live cells increased with the increase of the pH. Both the pseudo-first order and pseudo-second order models can satisfactorily interpret the adsorption by live and dead cells. Three isothermal adsorption models (Langmuir, Freundlich, and Sips) were used to fit the adsorption process. The adsorption of uranium by live and dead cells was best fitted by the Sips model. The maximal adsorption capacities of U(VI) by live and dead cells were 140.7 mg g-1 and 205.7 mg g-1, respectively. The mechanisms of U(VI) adsorption by Sphingopyxis sp. YF1 were revealed. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) show that U(VI) was deposited on the surface of the bacterial cells. Fourier-transform infrared spectroscopy (FTIR) shows that amine, hydroxyl, alkyl, amide I, amide II, phosphate, carboxylates and carboxylic acids were the major functional groups that are involved in U(VI) adsorption by live and dead cells. X-ray photoelectron spectroscopy (XPS) suggests that the main functional groups of live cells involved in adsorption were O = C-O, C-OH/C-O-C and N-C = O. This study indicates Sphingopyxis sp. YF1 is a high-efficiency U(VI)-adsorbing strain, promising to remove U(VI) from aquatic environment.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

A novel and capable supported phenylazophenylenediamine-based nano-adsorbent for removal of the Pb, Cd, and Ni ions from aqueous solutions

Herein, we report the synthesis and characterization of chrysoidine (4-phenylazo-m-phenylenediamine) grafted on magnetic nanoparticles (Fe₃O₄@SiO₂@CPTMS@PhAzPhDA = FeSiPAPDA) as a novel and versatile adsorbent used for the satisfactory removal of Pb, Ni, and Cd ions from contaminated water via the formation of their complexes. The Freundlich, Langmuir, Temkin, and Redlich-Patterson isotherm models were studied to reveal the adsorption capability of the adsorbent and were found out that the Langmuir model is more compatible with the nano-adsorbent behavior. Moreover, according to the ICP tests as well as based on the Langmuir isotherm, the maximum adsorption capacity of the FeSiPAPDA-based adsorbent for the Pb ions (97.58) is more than that of Cd (78.59) and Ni ions (64.03).

Efficient removal of Cd2+ by diatom frustules self-modified in situ with intercellular organic components

The organic modification of three-dimensional porous diatom frustules (biosilica) and their fossils (diatomite) is promising in heavy metal adsorption. However, the preparation of such materials involves complex processes, high costs, and environmental hazards. In this study, organic-biosilica composites based on in situ self-modification of diatoms were prepared by freeze-drying pretreatment. Freeze-drying resulted in the release of the intercellular organic components of diatoms, followed by loading on the surface of their diatom frustules. The bio-adsorbent exhibits outstanding Cd²⁺ adsorption capacity (up to 220.3 mg/g). The adsorption isotherms fitted the Langmuir model and the maximum adsorption capacity was 4 times greater than that of diatom biosilica (54.1 mg/g). The adsorption kinetics of Cd²⁺ was adequately described by a pseudo-second-order model and reached equilibrium within 30 min. By combining focused ion beam thinning with transmission electron microscopy-energy dispersive X-ray spectroscopy, the internal structure of the composite and the Cd²⁺ distribution were investigated. The results showed that the organic matter of the composite adsorbed approximately 10 times more Cd²⁺ than inorganic biosilica. The adsorption mechanism was dominated by complexation between the abundant organic functional groups (amide, carboxyl, and amino groups) on the surfaces of composite and Cd²⁺. The bio-adsorbent was demonstrated to have wide applicability in the presence of competitive cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and under a wide range of pH (3-10) conditions. Thus, the self-modification of diatoms offers a promising organic-inorganic composite for heavy metal remediation.

Insight into biofilm-forming patterns: biofilm-forming conditions and dynamic changes in extracellular polymer substances

The microbial biofilm adheres to the surface of the carrier, which protects the pollutant-degrading bacteria and resists harsh environments; thus, research on biofilm-forming patterns will help promote the application of biofilms in wastewater treatment. Herein, univariate analysis and response surface methodology (RSM) confirmed that glucose and mannose at 3-5 g/L promoted biofilm formation. Notably, the microplate method demonstrated that compared to trivalent cations, divalent cations could more greatly enhance the activity (especially magnesium) of the biofilm matrix, and the period of biofilm formation in the three strains was divided into the following stages: initial attachment (0-10 h), microcolony (10-24 h), maturation (24-48 h), and dispersion (36-72 h). During maturation, large amounts of extracellular polysaccharides (EPs) and extracellular DNA (eDNA) were distributed in the extracellular and intracellular spaces, respectively, as observed by super-resolution structured illumination microscopy (SR-SIM). This study enhances the understanding of the characteristics and patterns of biofilm formation and can facilitate the application of biofilms in wastewater treatment.

Dynamics, gene transfer, and ecological function of intracellular and extracellular DNA in environmental microbiome

Extracellular DNA (eDNA) and intracellular DNA (iDNA) extensively exist in both terrestrial and aquatic environment systems and have been found to play a significant role in the nutrient cycling and genetic information transmission between the environment and microorganisms. As inert DNA sequences, eDNA is able to present stability in the environment from the ribosome enzyme lysis, therein acting as the historical genetic information archive of the microbiome. As a consequence, both eDNA and iDNA can shed light on the functional gene variety and the corresponding microbial activity. In addition, eDNA is a ubiquitous composition of the cell membrane, which exerts a great impact on the resistance of outer stress from environmental pollutants, such as heavy metals, antibiotics, pesticides, and so on. This study focuses on the environmental dynamics and the ecological functions of the eDNA and iDNA from the perspectives of environmental behavior, genetic information transmission, resistance to the environmental contaminants, and so on. By reviewing the status quo and the future vista of the e/iDNAs research, this article sheds light on exploring the ecological functioning of the e/iDNAs in the environmental microbiome.