Bioremediation Of Environments Research Articles

Nitrite-Oxidizing Bacterial Strains Isolated from Soils of Andean Ecosystems and Their Potential Use in Nitrogen Reduction

Nitrification is part of the nitrogen cycle that occurs naturally in ecosystems. It is related to the presence of microorganisms and their metabolism, especially bacteria, which are involved in oxidizing compounds such as NH4+ and NO2− to NO3−. In this study, we evaluated the nitrification potential in 12 bacteria strains that belong to the genera Aeromonas, Bacillus, Buttiauxella, Mycobacterium, Paenibacillus, Serratia, and Yersenia, which are part of the cultivable microbial community from soil in a native forest and pine forest in The Labrado area within the Machangara micro-watershed in the Andes located in the south of Ecuador. This investigation aims to identify heterotrophic and lithoautotrophic strains using specific culture media for ammonium oxidative (AOL-AOH) and nitrate oxidation bacteria (ONL-ONH). The formation of nitrifying halos in the culture media allowed the identification of 10 strains with nitrifying potential. Five strains were from the pine forest, four were isolated from the native forest, and one strain was shared between both forests. The Serratia and Yersinia genera have a high NO2− oxidation capacity. Their inoculation in synthetic water rich in nitrogenous products allowed us to determine 40% and 94% nitrite reduction percentages and cell retention times of 20 to 40 days. Our results are promising for their possible potential use in environmental bioremediation processes through inoculation in wastewater for the biological removal of nitrogenous compounds.

Boronic Acid Moieties Stabilize Adhesion of Microalgal Biofilms on Glassy Substrates: A Chemical Tool for Environmental Applications.

Photosynthetic organisms such as diatoms microalgae provide innovative routes to eco-friendly technologies for environmental pollution bioremediation. Living diatoms are capable to incorporate in vivo a wide variety of chemical species dispersed in seawater, thus being promising candidates for eco-friendly removal of toxic contaminants. However, their exploitation requires immobilization methods that allow to confine microalgae during water treatment. Here we demonstrate that a biofilm of Phaeodactylum tricornutum diatom cells grown on the surface of a glassy substrate bearing boronic acid protruding moieties is stably anchored to the substrate resisting mechanical stress and it is suitable for removal of up to 80 % metal ions (As, Cr, Cu, Zn, Sn, Pb, Sb) in a model polluted water sample. Control experiments also suggest that stabilization of the biofilm adhesion occurs by interaction of boronic acid surface groups of the substrate with the hydroxyl groups of diatoms extracellular polysaccharides.

Comparative genomics provides insights into the phylogeny and environmental adaptations of Peritrichia (Protista, Ciliophora) – A potential resource for environmental pollution control and bioremediation

Peritrichs are one of the largest groups within the class Oligohymenophorea. They have a worldwide distribution and a high degree of species diversity. Using the single-cell genome sequencing technique, we obtained the genomes of five sessilid peritrichs. Combining both genomic and transcriptomic data of other publicly available oligohymenophorean ciliates (including the genomes of three sessilid peritrichs from our team’s previous study), we conducted a comparative genomics study. Our phylogenomic analyses using both maximum likelihood and Bayesian inference methods recovered the subclass Peritrichia and each of its two orders (Sessilida and Mobilida) as being monophyletic. The non-monophyly of two families (Vorticellidae and Zoothamniidae) was also well supported in both trees. Molecular clock analysis showed that the origin of the subclass Peritrichia was estimated to be during the late Proterozoic. We also analyzed the stop codon usage of 44 oligohymenophoreans. The results showed that most of these species used TGA as the biased stop codon and reassigned the other two stop codons (TAA and TAG) to code amino acids. In addition, we found that the presence of a typical peritrich lorica is a plesiomorphic character of the family Vaginicolidae. Through GO enrichment analysis for group-specific orthogroups of Vaginicolidae, we successfully identified the biological process and molecular function GO terms that were linked with the typical peritrich lorica, including three glycosaminoglycan-related and two chitin-related GO terms. Finally, our enrichment analyses of significantly expanded gene families in Peritrichia found that sessilids were more tolerant to environmental stress (mainly organic matter) than mobilids, suggesting that peritrich lineages (especially sessilids) may have the potential for application in environmental pollution control and bioremediation. Together, the results presented in this study will facilitate wider genome-scale phylogenetic analyses of Peritrichia and deepen the understanding of their unique advantages for environmental pollution control bioremediation.

Biodegradation of atrazine using selected marine bacteria: Possibilities for treating pesticide - contaminated wastewater

The use of pesticides including atrazine can cause detrimental problems to the environment. Atrazine, 2-chloro-4-(ethylamine)-6- (isopropyl amine)-s-triazine, is one of the widely used herbicides. In this work, thirteen pure bacterial strains were isolated from water and sediments collected from different sites along Alexandria Mediterranean Coast and were evaluated for their efficacy to biodegrade atrazine at three elevated concentrations (I: 109, II: 299 &III: 438 mg/L) for 7 days. Atrazine residues were determined using gas chromatography (GC). Marine isolates exhibited very high atrazine biodegradation with removal efficacy ranging between 15.79 and 75.49, 77.97–97.13 and 27.4–87.6% at three elevated concentrations, respectively. The results indicated that 5 of the isolates (E7, 8, 9, 11 and 13) were the most efficient, and active as atrazine bio-degraders. They were affiliated as Bacillus pacificus strain MCCC 1A06182 (E7 and E8), Bacillus cereus strain ATCC 14579 (E9) and Bacillus paramycoides strain MCCC 1A04098 (E11 and E13). Results obtained provided evidence that marine environment is a natural, rich and renewable source of bacteria with marvelous metabolic capabilities for efficient bioremediation of atrazine-contaminated aquatic environments or wastewater.

Aerobic biodegradation of phenanthrene by a newly isolated Klebsiella sp. DS-1 from wastewater

Representative polycyclic aromatic hydrocarbons (PAHs) compounds such as phenanthrene (PHE) derived from multiple anthropogenic activities are contributing to a growing number of concerns about its threats to the global water environment and human health. Microbial degradation is considered to be an increasingly promising approach for PHE removal, while effective PHE biodegraders from in situ environments are yet to be identified and their underlying degradation mechanisms still remain to be understood. Herein, a Klebsiella sp. strain DS-1 was isolated from petrochemical wastewater using PHE as the sole carbon source. The degradation efficiency of PHE was up to 88.4 % at 30 °C and pH 7 within a maximum of 9 days. DS-1 grew actively in wide ranges of environmental factors, such as pH values (5–9), temperature (20 °C–37 °C), and initial concentrations of PHE (20–200 mg/L), with the maintenance of PHE degradability. Genome analysis revealed 14 genes that were involved in PHE biodegradation by DS-1. Detection of metabolic intermediates revealed that strain DS-1 degraded PHE via the phthalic acid pathway. These findings have expanded the knowledge of Klebsiella sp. as an active PHE degrader in wastewater and indicate its potential in the bioremediation of PHE-contaminated aquatic environments.

Elucidating factors governing MICP biogeochemical processes at macro-scale: A reactive transport model development

Microbial Induced Calcium Carbonate Precipitation (MICP) influenced by biofilm metabolism in the subsurface can be exploited for a variety of engineered applications encompassing geotechnical ground improvement, environmental bioremediation, and hydraulic barriers. A reactive transport model was developed to determine the effects of controlling factors in terms of treatment protocols and experimental methods. Six column tests were calibrated and a range for the key parameters was determined. Fifteen key parameters of MICP reactive transport model were assessed in four categories (microbial activity and attachment, sample preparation, treatment protocol, and experiment dimensions). The results emphasized the effects of three main factors of microbial activity, microbial attachment process, and number of treatment (among all 15 assessed parameters) on the calcium carbonate (CaCO3) precipitation content and distribution. An increase in specific ureolysis rate (Ku) and attachment rate coefficient (Kat) by two orders of magnitude improves average CaCO3 by up to 13% and 6%, respectively with non-uniformity (COV) increase of 16%. Higher flow rates and solution concentrations contribute to more uniform CaCO3 distribution. The constant attachment rate model is useful to yield the CaCO3 precipitation profiles but more accurate models are needed to capture exact distribution. Post-treatment hydraulic conductivity, porosity and attached biomass were assessed.

Bioremediation of PAEs-contaminated saline soil: The application of a marine bacterial strain isolated from mangrove sediment

Phthalic acid esters (PAEs) are known as the most widely used plasticizer as well as one of the ubiquitously distributed emerging pollutants. Biodegradation and bioremediation via application of PAEs-degrading microbes is promising. In this study, a novel marine microbe, Gordonia hongkongensis RL-LY01, was isolated from mangrove sediment showing high di-(2-ethylhexyl) phthalate (DEHP) degradation capacity. Strain RL-LY01 could degrade a wide range of PAEs and the degradation kinetics of DEHP followed the first-order decay model. Meanwhile, good environmental adaptability, preference to alkaline conditions and good tolerance to salinity and metal ions was shown. Further, metabolic pathway of DEHP in strain RL-LY01 was proposed, with di-ethyl phthalate, phthalic acid, benzoic acid and catechol as intermediates. Additionally, one known mono-alkyl phthalate hydrolase gene (mehpH) was identified. Finally, the excellent performance during bioremediation of artificial DEHP-contaminated saline soil and sediment indicated strain RL-LY01 employs great application potential for the bioremediation of PAE-contaminated environments.

Developing a PAM-Flexible CRISPR-Mediated Dual-Deaminase Base Editor to Regulate Extracellular Electron Transport in Shewanella oneidensis.

Shewanella oneidensis MR-1 is a promising electroactive microorganism in environmental bioremediation, bioenergy generation, and bioproduct synthesis. Accelerating the extracellular electron transfer (EET) pathway that enables efficient electron exchange between microbes and extracellular substances is critical for improving its electrochemical properties. However, the potential genomic engineering strategies for enhancing EET capabilities are still limited. Here, we developed a clustered regularly interspaced short palindromic repeats (CRISPR)-mediated dual-deaminase base editing system, named in situ protospacer-adjacent motif (PAM)-flexible dual base editing regulatory system (iSpider), for precise and high-throughput genomic manipulation. The iSpider enabled simultaneous C-to-T and A-to-G conversions with high diversity and efficiency in S. oneidensis. By weakening DNA glycosylase-based repair pathway and tethering two copies of adenosine deaminase, the A-to-G editing efficiency was obviously improved. As a proof-of-concept study, the iSpider was adapted to achieve multiplexed base editing for the regulation of the riboflavin biosynthesis pathway, and the optimized strain showed an approximately three-fold increase in riboflavin production. Moreover, the iSpider was also applied to evolve the performance of an inner membrane component CymA implicated in EET, and one beneficial mutant facilitating electron transfer could be rapidly identified. Taken together, our study demonstrates that the iSpider allows efficient base editing in a PAM-flexible manner, providing insights into the design of novel genomic tools for Shewanella engineering.

The shifting research landscape for PAH bioremediation in water environment: a bibliometric analysis on three decades of development.

Polycyclic aromatic hydrocarbons (PAHs) with their carcinogenic, teratogenic, and mutagenic effects can cause great damage to the ecosystem and public health when present in water. With bioremediation, PAH contamination in water environment can be greatly reduced in an eco-friendly manner. It has thus become the research focus for many environmental scientists. In this study, a bibliometric analysis on three-decade (1990-2022) development of PAH bioremediation in water environment was conducted from temporal and spatial dimensions using CiteSpace. A total of 2480 publications, obtained from Web of Science core collection database, were used to explore the basic characteristics, hotspots, and prospects of the research area. The results showed that (1) bioremediation/biodegradation of PAHs in water environment has been getting researchers' attention since 1990, and is gaining even more traction as time goes on. (2) In terms of countries, China and the USA were the major contributors in this research area, while at the institutional level, the Chinese Academy of Sciences has produced the most research results. However, international cooperation across regions was lacking in the field. (3) Environment Science and Technology, Chemosphere, Applied and Environment Microbiology, Journal of Hazardous Materials, and Environment Pollution were the 5 most cited journals in this field. (4) There were three major stages the field has gone through, each with distinct research hotspots, including initial stage (1990-1994), mechanism investigation (1995-2000), and application exploration (2001-2010; 2011-2022). Finally, research perspectives were proposed, covering three directions, namely, bioavailability, immobilization, and viable but nonculturable (VBNC) bacteria.

Evaluating the microcystin-LR-degrading potential of bacteria growing in extreme and polluted environments

Inhabitants of extreme and polluted environments are attractive as candidates for environmental bioremediation. Bacteria growing in oil refinery effluents, tannery dumpsite soils, car wash effluents, salt pans and hot springs were screened for microcystin-LR biodegradation potentials. Using a colorimetric BIOLOG MT2 assay; Arthrobacter sp. B105, Arthrobacter junii, Plantibacter sp. PDD-56b-14, Acinetobacter sp. DUT-2, Salinivibrio sp. YH4, Bacillus sp., Bacillus thuringiensis and Lysinibacillus boronitolerans could grow in the presence of microcystin-LR at 1, 10 and 100 µg L−1. Most bacteria grew optimally at 10 µg L−1 microcystin-LR under alkaline pH (8 and 9). The ability of these bacteria to use MC-LR as a growth substrate depicts their ability to metabolize the toxin, which is equivalent to its degradation. Through PCR screening, these bacteria were shown to lack the mlr genes implying possible use of a unique microcystin-LR degradation pathway. The study highlights the wide environmental and taxonomic distribution of microcystin-LR degraders.

Effectively facilitating the degradation of chloramphenicol by the synergism of Shewanella oneidensis MR-1 and the metal-organic framework

Electroactive bacteria (EAB) and metal oxides are capable of synergistically removing chloramphenicol (CAP). However, the effects of redox-active metal-organic frameworks (MOFs) on CAP degradation with EAB are not yet known. This study investigated the synergism of iron-based MOFs (Fe-MIL-101) and Shewanella oneidensis MR-1 on CAP degradation. 0.5 g/L Fe-MIL-101 with more possible active sites led to a three-fold higher CAP removal rate in the synergistic system with MR-1 (initial bacterial concentration of 0.2 at OD600), and showed a superior catalytic effect than exogenously added Fe(III)/Fe(II) or magnetite. Mass spectrometry revealed that CAP was transformed into smaller molecular weight and less toxic metabolites in cultures. Transcriptomic analysis showed that Fe-MIL-101 enhanced the expression of genes related to nitro and chlorinated contaminants degradation. Additionally, genes encoding hydrogenases and c-type cytochromes associated with extracellular electron transfer were significantly upregulated, which may contribute to the simultaneous bioreduction of CAP both intracellularly and extracellularly. These results indicated that Fe-MIL-101 can be used as a catalyst to synergize with EAB to effectively facilitate CAP degradation, which might shed new light on the application in the in situ bioremediation of antibiotic-contaminated environments.

Breeding, Biosorption Characteristics, and Mechanism of a Lead-Resistant Strain.

To effectively carry out the bioremediation of a Pb2+ polluted environment, a lead-tolerant strain named D1 was screened from the activated sludge of a factory in Hefei, and its lead removal in a solution with Pb2+ concentration of 200 mg/L could reach 91% under optimal culture conditions. Morphological observation and 16S rRNA gene sequencing were used to identify D1 accurately, and its cultural characteristics and lead removal mechanism were also preliminarily studied. The results showed that the D1 strain was preliminarily identified as the Sphingobacterium mizutaii strain. The experiments conducted via orthogonal test showed that the optimal conditions for the growth of strain D1 were pH 7, inoculum volume 6%, 35 °C, and rotational speed 150 r/min. According to the results of scanning electron microscopy and energy spectrum analysis before and after the D1 exposure to lead, it is believed that the lead removal mechanism of D1 is surface adsorption. The Fourier transform infrared spectroscopy (FTIR) results revealed that multiple functional groups on the surface of the bacterial cells are involved in the Pb adsorption process. In conclusion, the D1 strain has excellent application prospects in the bioremediation of lead-contaminated environments.

Characterization and Production of a Biosurfactant Viscosin from Pseudomonas sp. HN11 and its Application on Enhanced oil Recovery During oily Sludge Cleaning.

Biosurfactants are renewable resources with versatile applications on environmental bioremediation and industrial processes. Pseudomonas species are one of the promising biosurfactant producers. However, besides rhamnolipids, little is known about Pseudomonas-derived biosurfactants on solubilization of polycyclic aromatic hydrocarbons (PAHs) and oily sludge treatment. In this study, Pseudomonas sp. HN11-derived biosurfactant was purified by chromatographic methods and was characterized as viscosin via bioinformatic analysis, spectrometric and spectroscopic analyses, Marfey's method and (C-H)α NMR fingerprint matching approach. Viscosin is a potent biosurfactant with critical micelle concentration of 5.79mg/L and is stable under various stresses. Moreover, viscosin was produced at 0.42g/L at 48h of liquid fermentation. Further data have shown that emulsifying agent viscosin is capable of promoting the solubilization of PAHs and displays enhanced oil recovery during oily sludge treatment. More specifically, viscosin has shown significantly enhanced solubilization on fluoranthene compared with control (0.04mg/L), 2.21mg/L and 1.27mg/L fluoranthene was recovered from 100mg/L and 200mg/L viscosin treatment, respectively. However, only 200mg/L viscosin has significantly enhanced the solubilization of phenanthrene (0.75mg/L) and benzo[a]pyrene (0.51mg/L) compared to each control (0.23mg/L for phenanthrene and 0.09mg/L for benzo[a]pyrene). Viscosin treatment of oily sludge (recovering of 0.58g oil) has shown a significant oil recovery compared to that of control (recovering of 0.42g oil). This study shows the great potential of viscosin-type biosurfactant on oily sludge treatment.

Immobilization of Klebsiella jilinsis strain 2N3 by corn straw biochar enhanced the degradation of nicosulfuron and restores the soil microbiome function and composition

Investigations on the bioremediation of nicosulfuron-contaminated soil environments based on biochar-immobilized bacteria are sparse. In this study, we characterized the degradation of nicosulfuron by Klebsiella jilinsis strain 2N3 with the highest degradation rate (92.62 %) and the optimal degrading conditions identified. Then, the strain 2N3 was further immobilized with corn straw biochar (BC 2N3) to enhance its degrading of nicosulfuron. The results of liquid chromatography showed that the treatment of BC 2N3 significantly shortened the half-life of nicosulfuron in non-sterilized soil from 22.8 to 5.1 days and recovered the enzymatic activities of urease, sucrase, dehydrogenase, and catalase involved in the degradation of soil pollutants. Surprisingly, results of 16S rRNA sequencing showed that BC 2N3 efficiently recovered the bacterial taxa with decreased relative abundances under the nicosulfuron stress, and significantly enhanced the degradation and metabolic pathways of nicosulfuron in soil. The vegetative growth of two nicosulfuron-sensitive crops (i.e., oilseed rape and wheat) was significantly increased in soil remediated by BC 2N3. Our results demonstrated that BC 2N3 efficiently degraded the nicosulfuron residues, providing a potentially promising bioremediation approach for improving the biological properties of herbicide-contaminated soil.

The mechanism of Se(IV) multisystem resistance in Stenotrophomonas sp. EGS12 and its prospect in selenium-contaminated environment remediation

Human activities have led to elevated levels of selenium (Se) in the environment, which poses a threat to ecosystems and human health. Stenotrophomonas sp. EGS12 (EGS12) has been identified as a potential candidate for the bioremediation of repair selenium-contaminated environment because of its ability to efficiently reduce Se(IV) to form selenium nanospheres (SeNPs). To better understand the molecular mechanism of EGS12 in response to Se(IV) stress, a combination of transmission electron microscopy (TEM), genome sequencing techniques, metabolomics and transcriptomics were employed. The results indicated that under 2 mM Se(IV) stress, 132 differential metabolites (DEMs) were identified, and they were significantly enriched in metabolic pathways such as glutathione metabolism and amino acid metabolism. Under the Se(IV) stress of 2 mM, 662 differential genes (DEGs) involved in heavy metal transport, stress response, and toxin synthesis were identified in EGS12. These findings suggest that EGS12 may respond to Se(IV) stress by engaging various mechanisms such as forming biofilms, repairing damaged cell walls/cell membranes, reducing Se(IV) translocation into cells, increasing Se(IV) efflux, multiplying Se(IV) reduction pathways and expelling SeNPs through cell lysis and vesicular transport. The study also discusses the potential of EGS12 to repair Se contamination alone and co-repair with Se-tolerant plants (e.g. Cardamine enshiensis). Our work provides new insights into microbial tolerance to heavy metals and offers valuable information for bio-remediation techniques on Se(IV) contamination.

Degradation of dibutyl phthalate and diethyl phthalate by indigenous isolate Bacillus sp. MY156

Dibutyl phthalate (DBP) and diethyl phthalate (DEP) are among the most extensively utilized plasticizers and widely exist in the environment causing adverse effect on human health. Previous studies on these phthalic acid esters (PAEs) biodegradation mainly involved individual substrates. However, these contaminants are more possible existed in mixtures. This work explored the biodegradation of DBP and DEP and their interactions using the indigenous isolate Bacillus sp. MY156. The results demonstrate DBP could be completely degraded by strain MY156 with high efficiency, while DEP showed relatively lower removal efficiency (72%) in 120 h. The binary substrate removal results revealed the coexistence of DBP and DEP had no significant influence on the degradation of each under the optimal pH and temperature. Nevertheless, slight retardation of the removal efficiency for DEP noticed as co-existed with DBP demonstrated their removal was possibly affected through the substrate competition. The dehydrogenase activity assay illustrated the behaviors of dehydrogenases caused by long-side chains PAEs were higher than PAEs with shorter alkyl chains. The isolate Bacillus sp. MY156 showed a positive utilization potentiality for bioremediation of PAEs-polluted environment.

High-efficiency degradation of methomyl by the novel bacterial consortium MF0904: Performance, structural analysis, metabolic pathways, and environmental bioremediation

Methomyl is a widely used carbamate pesticide, which has adverse biological effects and poses a serious threat to ecological environments and human health. Several bacterial isolates have been investigated for removing methomyl from environment. However, low degradation efficiency and poor environmental adaptability of pure cultures severely limits their potential for bioremediation of methomyl-contaminated environment. Here, a novel microbial consortium, MF0904, can degrade 100% of 25 mg/L methomyl within 96 h, an efficiency higher than that of any other consortia or pure microbes reported so far. The sequencing analysis revealed that Pandoraea, Stenotrophomonas and Paracoccus were the predominant members of MF0904 in the degradation process, suggesting that these genera might play pivotal roles in methomyl biodegradation. Moreover, five new metabolites including ethanamine, 1,2-dimethyldisulfane, 2-hydroxyacetonitrile, N-hydroxyacetamide, and acetaldehyde were identified using gas chromatography–mass spectrometry, indicating that methomyl could be degraded firstly by hydrolysis of its ester bond, followed by cleavage of the C–S ring and subsequent metabolism. Furthermore, MF0904 can successfully colonize and substantially enhance methomyl degradation in different soils, with complete degradation of 25 mg/L methomyl within 96 and 72 h in sterile and nonsterile soil, respectively. Together, the discovery of microbial consortium MF0904 fills a gap in the synergistic metabolism of methomyl at the community level and provides a potential candidate for bioremediation applications.

LA multiple PAHs-degrading Shinella sp. strain and its potential bioremediation in wastewater

Polycyclic aromatic hydrocarbons (PAHs) and heterocyclic derivatives are organic pollutants which threaten ecosystems and human beings. In this study, a new strain, Shinella sp. FLN 14, was isolated and characterized. It can utilize fluorene as its sole carbon source and effectively co-metabolize multiple PAHs and heterocyclic derivatives, including phenanthrene, acenaphthene, and fluoranthene. Two possible metabolic pathways are proposed (i.e., salicylic acid pathway and phthalic acid pathway). Whole-genome sequencing revealed that strain FLN14 possesses a chromosome and four plasmids. However, when combined with ensemble genetic information, novel fluorene-degrading functional gene clusters were not located within the genome of FLN 14, except for some new dioxygenases and electron transport chains, which typically initiate the oxidation of aromatic compounds. In wastewater bioremediation, strain FLN14 removed nearly 95 % of PAHs within 5 days and maintained high degrading activity during the 18-day reaction compared to the control. Overall, our study provides a promising candidate to achieve bioremediation of PAHs-contaminated environments.

Cloning and rational modification of a cold-adapted esterase for phthalate esters and parabens degradation

Phthalate esters (PAEs) and parabens are environmental pollutants that can be toxic to human health. Herein, a cold-adapted esterase from the Mao-tofu metagenome named Est1260 was screened for its PAE-hydrolyzing potential in cold temperatures. The results showed that purified Est1260 could degrade a variety of PAEs and parabens at temperatures as low as 0 °C. After careful analysis of the structural information and molecular docking, site-saturation mutation was conducted at the identified hotspots. Protein expression of variant A1B6 doubled, and its thermal stability significantly improved (24 times) without sacrificing activity at low temperatures. In addition, Est1260 and its variants were activated by NaCl and demonstrated resistance to high concentrations of saline (up to 5 M), making it a potential biocatalyst for bioremediation of PAE and paraben-polluted environments.

Nitrobenzene reduction promoted by the integration of carbon nanotubes and Geobacter sulfurreducens

Electron shuttles (ES) can mediate long-distance electron transfer between extracellular respiratory bacteria (ERB) and the surroundings. However, the effects of graphite structure in ES on the extracellular electron transfer (EET) process remain ambiguous. This work investigated the function of graphite structure in the process of nitrobenzene (NB) degradation by Geobacter sulfurreducens PCA, in which highly aromatic carbon nanotubes (CNTs) was studied as a typical ES. The results showed that the addition of 1.5 g L−1 of CNTs improved the NB biodegradation up to 81.2%, plus 18.8% NB loss due to the adsorption property of CNTs, achieving complete removal of 200 μM NB within 9 h. The amendment of CNTs greatly increased the EET rate, indicating that graphite structure exhibited excellent electron shuttle performance. Furthermore, Raman spectrum proved that CNTs obtained better graphite structure after 90 h of cultivation with strain PCA, resulting in higher electrochemical performance. Also, CNTs was perceived as the “Contaminant Reservoir”, which alleviated the toxic effect of NB and shortened the distance of EET process. Overall, this work focused on the effects of material graphite structure on the EET process, which enriched the understanding of the interaction between CNTs and ERB, and these results might promote their application in the in-situ bioremediation of nitroaromatic-polluted environment.