Assessment of PAH degradation potential of native species from a coking plant through identifying of the beneficial bacterial community within the rhizosphere soil

Toxicity of soil leaching liquor from coking plant in developmental zebrafish embryos/larvae model

The coking industry in China is the largest coke supplier in the world. Contaminated soil in industrial areas poses a serious threat to human and ecosystems. Most of the studies investigated the toxicity of soil from coking plant on soil microorganisms, while the toxic effects of soil leaching liquor on aquatics are limited. In this study, the composition of soil leaching liquor from a coking plant in Taiyuan (TY) was analyzed, and the developmental toxicity on zebrafish was evaluated. The results showed that a total of 91 polycyclic aromatic hydrocarbons were detected in the leaching liquor, followed by phenols and benzene series. The leaching liquor induced developmental impairment in zebrafish larvae, including delayed incubation, deficits in locomotor behavior, vascular and cardiac dysplasia, and impaired neurodevelopment. The results of metabolomics analysis showed that TY soil leaching liquor induced significant metabolic profile disturbances in zebrafish embryos/larvae. The developmental toxicity of the leaching liquor metabolic disorders may be associated with the leaching liquor-induced abnormalities in zebrafish embryonic development. Metabolic pathways were identified by arginine and proline metabolism, phosphotransferase system, starch and sucrose metabolism, steroid biosynthesis, beta-alanine metabolism, and nucleotide metabolism pathways.

Transformation and Degradation of PAH Mixture in Contaminated Sites: Clarifying Their Interactions with Native Soil Organisms

Soil contamination of polycyclic aromatic hydrocarbons (PAHs), especially caused by the mixture of two or more PAHs, raised great environmental concerns. However, research on the migration and transformation processes of PAHs in soils and their interactions with native communities is limited. In this work, soil samples from uncontaminated sites around the industrial parks in Handan, Hengshui, and Shanghai were artificially supplemented with three concentrations of anthracene (Ant), 9-chloroanthracene (9-ClAnt), benzopyrene (BaP), and chrysene (Chr). Ryegrass was planted to investigate the degradation of PAHs and its interaction with native soil organisms in the constructed ryegrass-microbe-soil microcosmic system. The bacterial and fungal communities in soil were affected by PAHs; their species diversity and relative abundance changed after exposure to different concentrations of PAHs, among which Lysobacter, Bacillus, Pseudomonas, and Massilia bacteria were correlated to the degradation of PAHs. On the 56th day, the contents of BaP, Chr, and Ant decreased with the degradation process, while the degradation of 9-ClAnt was limited. Nineteen intermediates, including hydroxylation and carboxylated compounds, were identified. The present research would help clarify the potential interactions between PAHs and native organisms in contaminated sites, providing fundamental information for evaluating the transformation risks of PAHs in the natural environment.

Construction of an effective method combining in situ capping with electric field-enhanced biodegradation for treating PAH-contaminated soil at abandoned coking sites

The simultaneous application of in situ capping and electro-enhanced biodegradation may be a suitable method for ensuring the feasibility and safety of reusing abandoned coking sites. However, the capping layer type and applied electric field pattern may affect the efficiency of sequestering and removing pollutants. This study investigated changes in electric current, soil moisture content and pH, polycyclic aromatic hydrocarbon (PAH) concentration, bacterial number, and microbial community structure and metabolic function during soil remediation at abandoned coking plant sites under different applied electric field patterns and barrier types. The results indicated that polarity-reversal electric field was more conducive to maintaining electric current, soil properties, resulting in higher microbial number, community diversity, and functional gene abundance. At 21d, the mean PAH concentrations in contaminated soil, the capping layer's clean soil and barrier were 78.79, 7.56, and 1.57 mg kg-1 lower than those with a unidirectional electric field, respectively. The mean degradation rate of PAHs in the bio-barrier was 10.12 % higher than that in the C-Fe barrier. In the experiment combining a polarity-reversal electric field and a bio-barrier, the mean PAH concentrations in contaminated soil and the capping layer were 706.68 and 27.15 mg kg-1 lower than those in other experiments, respectively, and no PAHs were detected in the clean soil, demonstrating that the combination of the polarity-reversal electric field and the bio-barrier was effective in treating soil at abandoned coking plant sites. The established method of combining in situ capping with electro-enhanced biodegradation will provide technical support for the treatment and reuse of heavily PAH-contaminated soil at abandoned coking plant sites.

Effect of Bio-Fertilizer Application on Agronomic Traits, Yield, and Nutrient Uptake of Barley (Hordeum vulgare) in Saline Soil

Under salinity conditions, growth and productivity of grain crops decrease, leading to inhibition and limited absorption of water and elements necessary for plant growth, osmotic imbalance, ionic stress, and oxidative stress. Microorganisms in bio-fertilizers have several mechanisms to provide benefits to crop plants and reduce the harmful effect of salinity. They can be effective in dissolving phosphate, fixing nitrogen, promoting plant growth, and can have a combination of all these qualities. During two successful agricultural seasons, two field experiments were conducted to evaluate the effect of bio-fertilizer applications, including phosphate solubilizing bacteria (PSB), nitrogen fixation bacteria and a mix of phosphate-solubilizing bacteria and nitrogen fixation bacteria with three rates, 50, 75 and 100% NPK, of the recommended dose of minimal fertilizer on agronomic traits, yield and nutrient uptake of barley (Hordeum vulgare) under saline condition in Village 13, Farafra Oasis, New Valley Governorate, Egypt. The results showed that the application of Microbein + 75% NPK recorded the highest values of plant height, spike length, number of spikes/m2, grain yield (Mg ha-1), straw yield (Mg ha-1), biological yield (Mg ha-1), protein content %, nitrogen (N), phosphorus (P), potassium (K) uptakes in grain and straw (kg ha-1), available nitrogen (mg/kg soil), available phosphorus (mg/kg soil), total microbial count of soil, antioxidant activity of soil (AOA), dehydrogenase, nitrogen fixers, and PSB counts. The application of bio-fertilizers led to an increase in plant tolerance to salt stress, plant growth, grain yield, and straw yield, in addition to the application of the bio-fertilizers, which resulted in a 25% saving in the cost of mineral fertilizers used in barley production.

Biochars assisted phytoremediation of polycyclic aromatic hydrocarbons contaminated agricultural soil: Dynamic responses of functional genes and microbial community

A biochar-intensified phytoremediation experiment was designed to investigate the dynamic effects of different biochars on polycyclic aromatic hydrocarbon (PAH) removal in ryegrass rhizosphere contaminated soil. Maize and wheat straw biochar pyrolyzed at 300 °C and 500 °C were amended into PAH-contaminated soil, and then ryegrass (Lolium multiflorum L.) was planted for 90 days. Spearman's correlations among PAH removal, enzyme activity, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHDα), and fungal and bacterial community structure were analyzed to elucidate the microbial degradation mechanisms during the combined remediation process. The results showed that 500 °C wheat straw biochar had higher surface area and more nutrients, and significantly accelerated the phytoremediation of PAHs (62.5 %), especially for high molecular weight PAH in contaminated soil. The activities of urease and dehydrogenase and the abundance of total and PAH-degrading bacteria, which improved with time by biochar and ryegrass, had a positive correlation with the removal rate of PAHs. Biochar enhanced the abundance of gram-negative (GN) PAH-RHDα genes. The GN PAH-degraders, Sphingomonas, bacteriap25, Haliangium, and Dongia may play vital roles in PAH degradation in biochar-amended rhizosphere soils. Principal coordinate analysis indicated that biochar led to significant differences in fungal community structures before 30 days, while the diversity of the bacterial community composition depended on planting ryegrass after 60 days. These findings imply that the structural reshaping of microbial communities results from incubation time and the selection of biochar and ryegrass in PAH-contaminated soils. Applying 500 °C wheat straw biochar could enhance the rhizoremediation of PAH-contaminated soil and benefit the soil microbial ecology.

Metagenomic analysis reveals the microbial response to petroleum contamination in oilfield soils

The response of the microbes to total petroleum hydrocarbons (TPHs) in three types of oilfield soils was researched using metagenomic analysis. The ranges of TPH concentrations in the grassland, abandoned well, working well soils were 1.16 × 102-3.50 × 102 mg/kg, 1.14 × 103-1.62 × 104 mg/kg, and 5.57 × 103-3.33 × 104 mg/kg, respectively. The highest concentration of n-alkanes and 16 PAHs were found in the working well soil of Shengli (SL) oilfield compared with those in Nanyang (NY) and Yanchang (YC) oilfields. The abandoned well soils showed a greater extent of petroleum biodegradation than the grassland and working well soils. Α-diversity indexes based on metagenomic taxonomy showed higher microbial diversity in grassland soils, whereas petroleum-degrading microbes Actinobacteria and Proteobacteria were more abundant in working and abandoned well soils. RDA demonstrated that low moisture content (MOI) in YC oilfield inhibited the accumulation of the petroleum-degrading microbes. Synergistic networks of functional genes and Spearman's correlation analysis showed that heavy petroleum contamination (over 2.10 × 104 mg/kg) negatively correlated with the abundance of the nitrogen fixation genes nifHK, however, in grassland soils, low petroleum content facilitated the accumulation of nitrogen fixation genes. A positive correlation was observed between the abundance of petroleum-degrading genes and denitrification genes (bphAa vs. nirD, todC vs. nirS, and nahB vs. nosZ), whereas a negative correlation was observed between alkB (alkane- degrading genes) and amo (ammonia oxidation), hao (nitrification). The ecotoxicity of petroleum contamination, coupled with petroleum hydrocarbons (PH) degradation competing with nitrifiers for ammonia inhibited ammonia oxidation and nitrification, whereas PH metabolism promoted the denitrification process. Moreover, positive correlations were observed between the abundance of amo gene and MOI, as well as between the abundance of the dissimilatory nitrate reduction gene nirA and clay content. Thus, improving the soil physicochemical properties is a promising approach for decreasing nitrogen loss and alleviating petroleum contamination in oilfield soils.

Response and adaptation of rhizosphere microbiome to organic pollutants with enriching pollutant-degraders and genes for bioremediation: A critical review

Phytoremediation largely involves microbial degradation of organic pollutants in rhizosphere for removing organic pollutants like polycyclic aromatic hydrocarbons, phthalates and polychlorinated biphenyls. Microbial community in rhizosphere experiences complex processes of response-adaptation-feedback up on exposure to organic pollutants. This review summarizes recent research on the response and adaptation of rhizosphere microbial community to the stress of organic pollutants, and discusses the enrichment of the pollutant-degrading microbial community and genes in the rhizosphere for promoting bioremediation. Soil pollution by organic contaminants often reduces the diversity of rhizosphere microbial community, and changes its functions. Responses vary among rhizosphere microbiomes up on different classes of organic pollutants (including co-contamination with heavy metals), plant species, root-associated niches (e.g., rhizosphere, rhizoplane and endosphere), geographical location and soil properties. Soil pollution can deplete some sensitive microbial taxa and enrich some tolerant microbial taxa in rhizosphere. Furthermore, rhizosphere enriches pollutant-degrading microbial community and functional genes including different gene clusters responsible for biodegradation of organic pollutants and their intermediates, which improve the adaptation of microbiome and enhance the remediation efficiency of the polluted soil. The knowledge gaps and future research challenges are highlighted on rhizosphere microbiome in response-adaptation-feedback processes to organic pollution and rhizoremediation. This review will hopefully update understanding on response-adaptation-feedback processes of rhizosphere microbiomes and rhizoremediation for the soil with organic pollutants.

Enhancement of electrokinetic-phytoremediation by Ophiopogon japonicus: stimulation of electrokinetic on root system and improvement of polycyclic aromatic hydrocarbon degradation

Root systems are sensitive to voltage and tend to improve the degradation of organic pollutants by promoting the root exudates and increasing microbial enzyme activity in the rhizosphere under the effect of electrokinetic. In this study, electrokinetic-assisted phytoremediation (EKPR) was applied for the remediation of soil containing phenanthrene (PHE) and pyrene (PYR). Direct current (DC) voltage (1 V cm-1) was applied across the soils for 30 days following 3 treatment schedules (0 h, 4 h, and 12 h per day), referred to as treatments EK0, EK4, and EK12. Electrokinetic assistance improved phytoremediation. Compared to EK0, the removal of PHE and PYR increased by 51.79% and 45.07% for EK4 and by 43.18% and 38.75% for EK12. The applied voltage promoted root growth, stimulated the root exudate release, and increased accumulation of PHE and PYR by plants, and the effect was most pronounced in treatment EK4. Catalase and urease activities in rhizosphere soil also increased, by respective increments of 44.51% and 40.86% for EK4 and by 28.53% and 21.24% for EK12. In this study, we demonstrated that a low voltage applied for an appropriate duration (4 h per day) improves removal of PAHs by stimulating root growth, promoting the root exudate release and enhancing enzyme activity in the microbiome of rhizosphere soil.

Improvement of carbon source composition reduces antibiotic resistance genes in the ectopic fermentation system

Effectively reduce antibiotic resistance genes (ARGs) in ectopic fermentation system (EFS) is essential for practical production. In this study, three experiments were performed to explore how to remove ARGs in EFS effectively. Results demonstrated that ARGs were easily enriched in rice-husk-sawdust padding; simultaneous addition of laccase and cellulase suppressed the ARGs, mainly by increasing soluble carbohydrate concentration and promoting humic acid concentration; addition of corn stalks into rice-husk-sawdust decreased the abundance of ARGs by improving the carbon source structure and enhancing cellulase activity. In conclusion, the present study provides a guidance to reduce the threat of ARGs in EFS, which paved a potential pathway to safely utilize manure resources.

Effects of bioaugmentation by isolated Achromobacter xylosoxidans BP1 on PAHs degradation and microbial community in contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic pollutants ubiquitous and persistent in soil. In order to provide a viable solution for bioremediation of PAHs-contaminated soil, a strain of Achromobacter xylosoxidans BP1 with superior PAHs degradation ability was isolated from contaminated soil at a coal chemical site in northern China. The degradation of phenanthrene (PHE) and benzo[a]pyrene (BaP) by strain BP1 was investigated in three different liquid phase cultures, and the removal rates of PHE and BaP by strain BP1 were 98.47% and 29.86% after 7 days under the conditions of PHE and BaP as the only carbon source, respectively. In the medium with the coexistence of PHE and BaP, the removal rates of BP1 were 89.44% and 9.42% after 7 days, respectively. Then, strain BP1 was investigated for its feasibility in remediating PAH-contaminated soil. Among the four PAHs-contaminated soils treated differently, the treatment inoculated with BP1 exhibited higher removal rates of PHE and BaP (p < 0.05), especially the CS-BP1 treatment (inoculation of BP1 into unsterilized PAHs-contaminated soil) showed 67.72%, 13.48% removal of PHE and BaP, respectively, over 49 days of incubation. Bioaugmentation also significantly increased the activity of dehydrogenase and catalase in the soil (p＜0.05). Furthermore, the effect of bioaugmentation on the removal of PAHs was investigated by measuring the activity of dehydrogenase (DH) and catalase (CAT) during incubation. Among them, the DH and CAT activities of CS-BP1 and SCS-BP1 (inoculation of BP1 into sterilized PAHs-contaminated soil) treatments inoculated with strain BP1 were significantly higher than those of treatments without BP1 addition during incubation (p < 0.01). The structure of the microbial community varied among treatments, but the Proteobacteria phylum showed the highest relative abundance in all treatments of the bioremediation process, and most of the bacteria with higher relative abundance at the genus level also belonged to the Proteobacteria phylum. Prediction of microbial functions in soil by FAPROTAX analysis showed that bioaugmentation enhanced microbial functions associated with the degradation of PAHs. These results demonstrate the effectiveness of Achromobacter xylosoxidans BP1 as a PAH-contaminated soil degrader for the risk control of PAHs contamination.

Effects of co-modified biochar immobilized laccase on remediation and bacterial community of PAHs-contaminated soil

Considering the stability and economy of immobilized enzymes, this study prepared co-modified biochar immobilized laccase product named Fe₃O₄@NaBC@GA@LC via orthogonal experimental design and explored its possibility of remediating polycyclic aromatic hydrocarbons (PAHs) contaminated soil in steel plants. Compared with the free laccase treatment, the relative activity of Fe₃O₄@NaBC@GA@LC remained 60 % after 50 days of incubation at room temperature. The relative activity of Fe₃O₄@NaBC@GA@LC could still retain nearly 80 % after five reuses. In the process of simulating the PAHs-contaminated site treatment experiment in Hangzhou Iron and steel plant, immobilized laccase exhibited efficient adsorption and degradation performances and even the removal rate of 5-ring PAHs reached more than 90 % in 40 days, resulting in improving urease activity and dehydrogenase in the soil and promoted the growth of a PAH degrading bacteria (Massilia). Our results further explained the efficient degradation effects of Fe₃O₄@NaBC@GA@LC on PAHs, which make it a promising candidate for PAHs-contaminated soil remediation.

Evaluation of rice straw and its transformation products on norfloxacin degradation and antibiotic resistome attenuation during soil incorporation

Straw incorporation into reclaimed soils has been demonstrated to increase soil nutrients and has the potential to efficiently increase crop production. However, which incorporation mode is more helpful in the control of antibiotic resistance genes (ARGs) remains unknown. In this study, we systematically compared the occurrence of antibiotic resistome in norfloxacin contaminated soils amended with rice straw (RS) and the transformation products, biochar (RSB) and ash (RSA). RS significantly promoted the degradation of norfloxacin (0.0648 d^-1, 3 times faster than control), whereas RSB had little effect and RSA hindered the degradation. Based on metagenomic analysis, RS and RSB significantly reduced the ARGs relative abundance (0.1421 and 0.1991 compared to 0.2540 in control) at the end of soil incubation. Adonis test indicated that all of amendment treatments significantly affect the microbial communities in soils, whereas only RS and RSB significantly affect the variation of antibiotic resistome. Procrustes analysis confirmed the association of microbial communities and ARGs. Network analysis further revealed that the reduction in Actinobacteria was the main reason for the general decrease of ARGs relative abundance during soil incorporation, whereas Proteobacteria and Bacteroidetes were responsible for temporary promotion of ARGs in RS and RSB at the early stage. Finally, scientifically setting up the usage of rice straw and optimizing the preparation process of biochar are suggested for the synchronous control of the risk of antibiotics and ARGs during soil incorporation.

Community response of soil microorganisms to combined contamination of polycyclic aromatic hydrocarbons and potentially toxic elements in a typical coking plant

Both polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs) of coking industries impose negative effects on the stability of soil ecosystem. Soil microbes are regarded as an essential moderator of biochemical processes and soil remediation, while their responses to PAHs-PTEs combined contamination are largely unknown. In the present study, soil microbial diversity and community composition in the typical coking plant under the chronic co-exposure of PAHs and PTEs were investigated and microbial interaction networks were built to reveal microbial co-occurrence patterns. The results indicated that the concentrations of PAHs in the soil inside the coking plant were significantly higher than those outside the plant. The mean concentration of ∑16PAHs was 2894.4 ng·g^-1, which is 5.58 times higher than that outside the plant. The average Hg concentration inside the coking plant was 22 times higher than the background value of Hebei province. The soil fungal community inside the coking plant showed lower richness compared with that of outside community, and there are significant difference in the bacterial and fungal community composition between inside and outside of coking plant (p < 0.01). Predicted contribution of different environmental factors to each dominant species based on random forest identified 20 and 25 biomarkers in bacteria and fungi, respectively, that were highly sensitive to coking plant soil in operation, such as Betaproteobacteria，Sordariomycetes and Dothideomycetes. Bacterial and fungal communities were shaped by the soil chemical properties (pH), PTEs (Hg), and PAHs together in the coking plant soils. Furthermore, the bacterial and fungal interaction patterns were investigated separately or jointly by intradomain and interdomain networks. Competition is the main strategy based on the co-exclusion pattern in fungal community, and the competitive relationship inside the coking plant is more complex than that outside the plant. In contrast, cooperation is the dominant strategy in bacterial networks based on the co-occurrence pattern. The present study provided insights into microbial response strategies and the interactions between bacteria and fungi under long-term combined contamination.

Saline-alkali stress reduces soil bacterial community diversity and soil enzyme activities

Saline-alkalisation of the soil environment and microorganism is a global challenge. However, relevant studies on the effects of saline-alkali stress on soil bacterial communities are limited. In this study, we investigated the effects of saline-alkali stress on the carbon source metabolic utilisation of the microbial community, bacterial diversity, and composition in soil using Biolog Ecoplate and 16S rRNA gene amplicon sequencing. Biolog Ecoplate results showed that saline-alkali stress decreased the metabolic activity and functional diversity, and changed the utilisation characteristics of carbon sources in soil microorganisms. Particularly, high level of saline-alkali stress significantly decreased the utilisation of carbohydrates and amino acids carbon sources. The results of 16S rRNA gene amplicon sequencing showed that high level of saline-alkali stress significantly reduced the diversity of soil bacterial communities. In addition, high level of saline-alkali stress significantly decreased the relative abundances of some key bacterial taxa, such as Gemmatimonas, Sphingomonas, and Bradyrhizobium. Furthermore, as saline-alkali content increased, the soil catalase, protease, urease, and sucrase activities also significantly decreased. Collectively, these results provide new insight for studies on the changes in the soil bacterial community and soil enzyme activity under saline-alkali stress.

Vertical profile and assessment of soil pollution from a typical coking plant by suspect screening and non-target screening using GC/QTOF-MS

A comprehensive workflow for suspect screening and non-target screening with gas chromatography coupled with quadrupole time-of-flight mass spectrometry (GC/QTOF-MS) was used to characterize the pollution characteristics of soil samples in a typical coking plant in China. Suspect screening confirmed 57 chemicals including PAHs, alkyl PAHs, and phthalates contained in high-resolution personal compound database and library (PCDL). Non-target screening detected 88 chemicals from soil samples in the NIST 17 library. A total of 122 chemicals were screened in soil samples, and many of them were of emerging concern. Their presence in the soil obtained from coking operations has been underestimated, such as the oxygenated PAHs (naphtho[2,1-b]furan and 9H-fluoren-9-one), and the alkyl biphenyls compounds (4,4'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 4-methyl-1,1'-biphenyl and 2,2',5,5'-tetramethyl-1,1'-biphenyl). Toxicity assays by luminescent bacteria proved that the extracts from soil samples at different depths showed varying toxicity to V. qinghaiensis sp.-Q67. Soil extracts from a depth of 20-40 cm exhibited the greatest toxicity to luminescent bacteria compared with the other six-layered soil samples, which was correlated with the number of detectable pollutants and total organic carbon content. This study provided a screening method for suspect and non-target contaminants in urban industrial soil sites, which was important in identifying localized contamination sources.

Straw return promoted the simultaneous elimination of sulfamethoxazole and related antibiotic resistance genes in the paddy soil

Straw return could provide a natural available carbon source for the soil microorganisms, which might affect the environmental behaviours of organic pollutants. In this study, microcosm system was constructed to investigate the effect of rice straw return on the fate of sulfamethoxazole (SMX) and related antibiotic resistance genes (ARGs). The results showed that straw return (1% of soil dry mass) could accelerate the degradation of SMX via co-metabolism. In the treatment group with rice straw, SMX was rapidly decomposed into small molecular compounds (e.g., (Z)-1-amino-3-oxobut-1-en-1-aminium and benzenesulfinic acid) within the first six days, and SMX was undetectable after 60 days; while for the SMX group without rice straw, 1.3 mg kg^-1 of SMX still remained at the 60th day. Straw return could enhance the relative abundances of Proteobacteria involved in SMX degradation, including Microvirga and Ramlibacter, which co-metabolized SMX via the degradation pathways of mineralizable components and aromatic compound. Furthermore, straw return significantly eliminated the ARGs. After 60 days, the int1 and sul1 abundances of the treatment group with rice straw were less than one-tenth of the SMX group without rice straw. The redundancy and network analysis of bacterial community and environmental factors showed that dissolved organic carbon and bacteria belonged to Proteobacteria and Actinobacteria might play positive roles in eliminating ARGs. Our results demonstrate that straw return could promote the simultaneous elimination of SMX and corresponding ARGs, which provides a promising approach to effectively treat antibiotics and ARGs in the farmland.

Mechanism of bio-electrokinetic remediation of pyrene contaminated soil: Effects of an electric field on the degradation pathway and microbial metabolic processes

In this study, the mechanism of bio-electrokinetic (BIO-EK) remediation to improve the degradation of pyrene was evaluated based on an analysis of the intermediate products and the microbial community. The results show that BIO-EK remediation has a higher pyrene degradation efficiency on pyrene and its intermediate products than the bioremediation and electrokinetic (EK) remediation processes. A series of intermediate products were detected. According to the type of the intermediate products, two degradation pathways, biological metabolism and electrochemical oxidation, are proposed in the BIO-EK remediation of pyrene. Furthermore, the primary microbial taxa involved in the pollutant degradation changed, which led to variations in the functional gene components. The abundant and functional genes related to metabolism were specifically analyzed. The results indicate that the electric field promotes the expression of metabolisms associated with 14 carbohydrates, 13 lipids, 13 amino acids, five energies, and in particular, 11 xenobiotics. These results suggest that in addition to the promotion effect on the microbial metabolism caused by the electric field, BIO-EK remediation can promote the degradation of pollutants due to the coexistence of a microbial metabolic pathway and an electrochemical oxidation pathway.

Temporal changes of microbial community structure and nitrogen cycling processes during the aerobic degradation of phenanthrene

Phenanthrene (PHE) is frequently detected in worldwide soils. But it is still not clear that how the microbial community succession happens and the nitrogen-cycling processes alter during PHE degradation. In this study, the temporal changes of soil microbial community composition and nitrogen-cycling processes during the biodegradation of PHE (12 μg g^-1) were explored. The results showed that the biodegradation of PHE followed the second-order kinetics with a half-life of 7 days. QPCR results demonstrated that the bacteria numbers increased by 67.1%-194.7% with PHE degradation, whereas, no significant change was observed in fungi numbers. Thus, high-throughput sequencing based on 16 S rRNA was conducted and showed that the abundances of Methylotenera, Comamonadaceae, and Nocardioides involved in PHE degradation and denitrification were significantly increased, while those of nitrogen-metabolism-related genera such as Nitrososphaeraceae, Nitrospira, Gemmatimonadacea were decreased in PHE-treated soil. Co-occurrence network analysis suggested that more complex interrelations were constructed, and Proteobacteria instead of Acidobacteriota formed intimate associations with other microbes in responding to PHE exposure. Additionally, the abundances of nifH and narG were significantly up-regulated in PHE-treated soil, while that of amoA especially AOAamoA was down-regulated. Finally, correlation analysis found several potential microbes (Methylotenera, Comamonadaceae, and Agromyces) that could couple PHE degradation and nitrogen transformation. This study confirmed that PHE could alter microbial community structure, change the native bacterial network, and disturb nitrogen-cycling processes.

Castro I, Soares R, Brito DRA, Mbanze AA, Chaúque A, Máguas C, Ezeokoli OT, Ribeiro NS, Marques I, Ribeiro-Barros AI. The Nexus between Fire and Soil Bacterial Diversity in the African Miombo Woodlands of Niassa Special Reserve, Mozambique

(1) Background: the Miombo woodlands comprise the most important vegetation from southern Africa and are dominated by tree legumes with an ecology highly driven by fires. Here, we report on the characterization of bacterial communities from the rhizosphere of Brachystegia boehmii in different soil types from areas subjected to different regimes. (2) Methods: bacterial communities were identified through Illumina MiSeq sequencing (16S rRNA). Vigna unguiculata was used as a trap to capture nitrogen-fixing bacteria and culture-dependent methods in selective media were used to isolate plant growth promoting bacteria (PGPB). PGP traits were analysed and molecular taxonomy of the purified isolates was performed. (3) Results: Bacterial communities in the Miombo rhizosphere are highly diverse and driven by soil type and fire regime. Independent of the soil or fire regime, the functional diversity was high, and the different consortia maintained the general functions. A diverse pool of diazotrophs was isolated, and included symbiotic (e.g., Mesorhizobium sp., Neorhizobium galegae, Rhizobium sp., and Ensifer adhaerens), and non-symbiotic (e.g., Agrobacterium sp., Burkholderia sp., Cohnella sp., Microvirga sp., Pseudomonas sp., and Stenotrophomonas sp.) bacteria. Several isolates presented cumulative PGP traits. (4) Conclusions: Although the dynamics of bacterial communities from the Miombo rhizosphere is driven by fire, the maintenance of high levels of diversity and functions remain unchanged, constituting a source of promising bacteria in terms of plant-beneficial activities such as mobilization and acquisition of nutrients, mitigation of abiotic stress, and modulation of plant hormone levels.