The regulation of rhizosphere bacterial community structure and metabolism by plants in municipal solid waste landfills is a key to enhancing the biodegradation of chlorobenzene (CB). In this study, we employed biodiversity and metabolomics methods to systematically analyze the mechanisms of different plant species in regulating the rhizosphere bacterial community structure and metabolic features and then improved the methane (CH₄) oxidation and CB degradation capacity. The results showed that the rhizosphere soil of Rumex acetosa exhibited the highest CH₄ oxidation and CB degradation capacity of 0.08 g/(kg·h) and 1.72×10^-6 g/(L·h), respectively, followed by the rhizosphere soil of Amaranthus spinosus L., with the rhizosphere soil of Broussonetia papyrifera showing the weakest activity. Rumex acetosa promoted the colonization of Methylocaldum in the rhizosphere, and the small-molecule organic amine, such as triethylamine and N-methyl-aniline, secreted from the roots of this plant enhanced the tricarboxylic acid cycle and nicotinamide metabolism, thereby increasing microbial activity and improving CH₄ and CB degradation efficiency. Conversely, cinnamic acid and its derivatives secreted by Broussonetia papyrifera acted as autotoxins, inhibiting microbial activity and exacerbating the negative effects of salt stress on key microbes such as methanotrophs. This study probed into the mechanisms of typical plants growing in landfill cover soil in regulating bacterial ecological functions, offering theoretical support and practical guidance for the plant-microbe joint control of landfill gas pollution.
Biodegradation, Environmental ; Rhizosphere ; Soil Microbiology ; Waste Disposal Facilities ; Chlorobenzenes/metabolism* ; Bacteria/metabolism* ; Soil Pollutants/metabolism* ; Methane/metabolism* ; Plant Roots/microbiology* ; Amaranthus/microbiology* ; Soil

Chlorobenzene contaminants (CBs) pose a threat to the eco-environment, and functional strains hold considerable potential for the remediation of CB-contaminated sites. To deeply explore the application potential of functional bacteria in the in-situ bioremediation of CBs, this study focused on the biodegradation characteristics and degradation kinetics of CB and 1, 2-dichlorobenzene (1, 2-DCB) in soil by the isolated strain Serratia marcescens TF-1. Additionally, an in-situ remediation trial was conducted with this strain at a chemical industrial site. Batch serum bottle experiments showed that the degradation rate of CB at the concentrations ranging from 20 to 200 mg/L by TF-1 was 0.22-0.66 mol/(g_cell·h), following the Haldane model, with the optimal concentration at 23.12 mg/L. The results from simulated soil degradation experiments indicated that the combined use of TF-1 and sodium succinate (SS) significantly enhanced the degradation of CBs, with the maximum degradation rate of CB reaching 0.104 d^-1 and a half-life of 6.66 d. For 1, 2-DCB, the maximum degradation rate constant was 0.068 7 d^-1, with a half-life of 10.087 d. The in-situ remediation results at the chemically contaminated site demonstrated that the introduction of bacterial inoculant and SS significantly improved the removal of CBs, achieving the removal rates of 84.2%-100% after 10 d. CB, 1, 4-dichlorobenzene (1, 4-DCB), and benzo[a]pyrene were completely removed. Microbial diversity analysis revealed that the in-situ remediation facilitated the colonization of TF-1 and the enrichment of indigenous nitrogen-fixing Azoarcus, which may have played a key role in the degradation process. This study provides a theoretical basis and practical experience for the in situ bioremediation of CBs-contaminated sites.
Chlorobenzenes/isolation & purification* ; Biodegradation, Environmental ; Soil Pollutants/isolation & purification* ; Serratia marcescens/metabolism* ; Industrial Waste ; Soil Microbiology

Landfill is one of the important sources of carbon tetrachloride (CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone (0-15 cm), anoxic zone (15-45 cm) and anaerobic zone (> 45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform (CF), dichloromethane (DCM) and Cl^- in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2-103.6 μg/(m²·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium, Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone, respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM, respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.
Bacteria/metabolism* ; Biodegradation, Environmental ; Carbon Tetrachloride/metabolism* ; Methane/metabolism* ; Waste Disposal Facilities

Chlorinated hydrocarbons (CAHs) threaten human health and the ecological environment due to their strong carcinogenic, teratogenic, mutagenic and heritable properties. Heterotrophic assimilation degradation can completely and effectively degrade CAHs, without secondary pollution. However, it is crucial to comprehensively understand the heterotrophic assimilation process of CAHs for its application. Therefore, we review here the characteristics and advantages of heterotrophic assimilation degradation of CAHs. Moreover, we systematically summarize current research status of heterotrophic assimilation of CAHs. Furthermore, we analyze bacterial genera and metabolism, key enzymes and characteristic genes involved in the metabolic process. Finally, we indicate existing problems of heterotrophic assimilation research and future research needs.
Bacteria ; metabolism ; Biodegradation, Environmental ; Hydrocarbons, Chlorinated ; metabolism ; Industrial Microbiology ; trends

Chlorinated aliphatic hydrocarbons (CAHs) with characteristics of high toxicity, biological accumulation and recalcitrance to degradation as well as carcinogenicity, teratogenesis and mutagenicity, are seriously harmful to human health and ecological environment. CAHs degradation depends on biotic and abiotic responses that exist diversified interactive effects, so it is important to clarify the mechanism of CAHs degradation via biotic and abiotic mutual promoting to significantly enhance the CAHs-contaminated site restoration. In this work, a series of pathways for CAHs degradation was first introduced and summarized as three means on reductive dechlorination, aerobic cometabolism and direct oxidation, and biotic and abiotic typical factors affecting CAHs degradation were concluded from these. Then, mechanisms of induced degradation and synergistic degradation were indicated from the perspective of mutual promoting degradation both with biotic and abiotic responses, and furthermore, the application and technical limitations of CAHs degradation enhanced via biotic and abiotic mutual promoting were reviewed and analyzed. Finally, the development of CAHs degradation technology in future was prospected.

Objective To investigate the mechanism of implanted tissue-engineered bone (TEB)recruiting endogenous mesenchymal stem cells (BMSCs) towards bone regeneration after traumatic bone defect.Methods In vivo experiments:2 mm of diaphysis and periosteum were removed from the middle of the femoral shaft in 8 week old FVB/N mice to form a large segment of bone defect.Demineralized bone matrix (DBM) and TEB were implanted into the defect area and fixated.All mice were randomly divided into DBM group (n =18) and TEB group (n =18).The results were observed 24 hours after implantation:(1) flow cytometry was used to evaluate the number of mobilized host BMSCs into the blood;(2) non-invasive bioluminescent imaging was used to observe the ability of two groups in recruiting mouse bone marrow derived mesenchymal stem cells (mBMSCs) in peripheral blood to the defect area;(3) ELISA was used to evaluate the stromal cell-derived factor 1 (SDF-1) content in peripheral blood of two groups.In vitro experiments:(1) transwell assay was conducted to evaluate the ability of SDF-1 (100 ng/ml) in promoting the migration of human bone marrow derived mesenchymal stem cells (hBMSCs).SDF-1/C-X-C motif chemokine receptor-4 (CXCR4) pathway was blocked by the selective CXCR4 antagonist Plerixafor (AMD3100).The experimental groups were divided into control group,SDF-1 group,and SDF-1 + AMD3100 group.(2) The co-culture system of human umbilical vein endothelial cells (hUVECs) and hBMSCs was established,and cells were stimulated by SDF-1.The experimental groups were divided into hBMSCs group,hBMSCs + hUVECs group,and hBMSCs + hUVECs (AMD3100 pretreatment) group.Transwell assays were used to compare the migration of hBMSCs in each group.ELISA was used to detect the concentration of hepatocyte growth factor (HGF) in the co-culture supernatant.(3) In vitro cultured hUVECs were stimulated by SDF-1 and SDF-1/CXCR4 pathway was antagonized by AMD3100.The experimental groups were divided into control group,SDF-1 group,and SDF-1 + AMD3100 group.Quantitative real-time polymerase chain reaction (qRT PCR) was used to evaluate the expression of HGF in each group.Results In vivo experiments:24 h after transplantation,the number of BMSCs and SDF-1 concentration in the TEB group were significantly highcr than those in the DBM group (P ＜ 0.05).The number of recruited mBMSCs into the circulation in the TEB group was larger than that in the DBM group (P＜ 0.01).In vitro experiments:(1) compared with the control group and the SDF-1 + AMD3100 group,the SDF-1 group significantly enhanced the migration ability of hBMSCs in Transwell migration experiments (P ＜ 0.01);(2) compared with the hBMSCs group and the hBMSCs + hUVECs (AMD3100 pretreatment) group,the number of migrated cells and HGF concentration in the hBMSCs + hUVEC group significantly increased (P ＜ 0.01),but there were no significant differences between the hBMSCs group and the hBMSCs + hUVECs (AMD3100 Pretreatment) group (P ＞0.05);(3) qRT-PCR showed that the expression of HGF was significantly increased in the SDF-1 group compared with the control group (P ＜ 0.05).After antagonizing SDF-1/CXCR4,HGF expression in the SDF-1 + AMD3100 group was significantly lower than that in the SDF-1 group.Conclusions TEB transplantation in traumatic bone defect can significantly increase the concentration of chemokine SDF-1 in vivo and effectively promote the mobilization of endogenous MSCs and recruitment of circulating MSCs.SDF-1 not only directly promotes the migration of hBMSCs through SDF-1/CXCR4 pathway,but also up-regulates the expression and secretion of HGF in vascular cells to further amplify the chemotactic effect of SDF-1 on hBMSCs.

We isolated and enriched mixed microorganisms SWA1 from landfill cover soils supplemented with trichloroethylene (TCE). The microbial mixture could degrade TCE effectively under aerobic conditions. Then, we investigated the effect of copper ion (0 to 15 μmol/L) on TCE biodegradation. Results show that the maximum TCE degradation speed was 29.60 nmol/min with 95.75% degradation when copper ion was at 0.03 μmol/L. In addition, genes encoding key enzymes during biodegradation were analyzed by Real-time quantitative reverse transcription PCR (RT-qPCR). The relative expression abundance of pmoA gene (4.22E-03) and mmoX gene (9.30E-06) was the highest when copper ion was at 0.03 μmol/L. Finally, we also used MiSeq pyrosequencing to investigate the diversity of microbial community. Methylocystaceae that can co-metabolic degrade TCE were the dominant microorganisms; other microorganisms with the function of direct oxidation of TCE were also included in SWA1 and the microbial diversity decreased significantly along with increasing of copper ion concentration. Based on the above results, variation of copper ion concentration affected the composition of SWA1 and degradation mechanism of TCE. The degradation mechanism of TCE included co-metabolism degradation of methanotrophs and oxidation metabolism directly at copper ion of 0.03 μmol/L. When copper ion at 5 μmol/L (biodegradation was 84.75%), the degradation mechanism of TCE included direct-degradation and co-metabolism degradation of methanotrophs and microorganisms containing phenol hydroxylase. Therefore, biodegradation of TCE by microorganisms was a complicated process, the degradation mechanism included co-metabolism degradation of methanotrophs and bio-oxidation of non-methanotrophs.
Biodegradation, Environmental ; Copper ; chemistry ; Methylocystaceae ; metabolism ; Oxidation-Reduction ; Soil Microbiology ; Trichloroethylene ; metabolism

OBJECTIVETo evaluate the results of managing the infected nonunions of distal tibial fractures combined with talar fracture and calcaneal fracture with tibial bone transport, tibiotalar or tibiocalcaneal arthrodesis using the hybrid external fixator.

METHODSA retrospective review of 26 patients who underwent either tibiotalar arthodesis or tibiocalcaneal arthodesis using an hybrid external fixator for infected nonunions of distal tibial fractures, talar and calcaneal fractures after tibial bone distraction was made. Each patient had a debridement of all infected and nonviable bones, the wound area were 2 cm×4 cm-4 cm×8 cm. The bony surfaces of distal tibia and talus were prepared for the fusion followed by application of an Orthofix's hybrid external fixator.

RESULTSThe remaining 18 patients undertook debridement at the docking sites, and 14 of them had autogenous bone grafting. There was a mean follow-up of 32 months (22-38 months). All the patients had successful fusions. There were no recurrent deep infections or amputations. Two patients had 6° of varus deformity at the docking site.

CONCLUSIONTibiotalar or tibiocalcaneal arthrodesis using the Ilizarov technique is viable alternative to amputation in patients with infected nonunions,especially if there is a large bone loss of the tibias, talus and calcaneus.

Amputation ; Ankle Injuries ; Ankle Joint ; Arthrodesis ; Bone Transplantation ; Calcaneus ; External Fixators ; Follow-Up Studies ; Foot Injuries ; Fractures, Bone ; Humans ; Ilizarov Technique ; Joint Dislocations ; Retrospective Studies ; Talus ; Tibia ; Tibial Fractures

Bioremediation is one of the most effective ways to treat and dispose of chlorinated hydrocarbons, and methanotrophs are potentially useful to do so. Recent studies found that facultative methanotrophs can use compounds containing C-C bond as sources of carbon and energy, thus overcoming the limitation that obligate methanotrophsone uses only C1 compounds for this process. This is a unique metabolic approach that is becoming increasingly attractive in the field of contaminant biodegradation. Here, we summarized the bioremediation of chlorinated hydrocarbons by obligate and facultative methanotrophs. This process involves the degradation of various chlorinated hydrocarbons by diverse strains, including pure cultures and mixed cultures. We also compare the activity expression and catalytic properties of different types of methane monooxygenases in various substrates. We furthermore summarize the kinetic characteristics of the degradation of chlorinated hydrocarbons using the model strain Methylosinus trichosporium OB3b, and outline the degradation and potential of chlorinated hydrocarbons by facultative methanotrophs. Lastly, we discuss current problems and future research directions for degradation of chlorinated hydrocarbons by methanotrophs.
Biodegradation, Environmental ; Hydrocarbons, Chlorinated ; metabolism ; Methylosinus trichosporium ; metabolism ; Oxygenases ; metabolism

Methanotrophs could degrade methane and various chlorinated hydrocarbons. The analysis on methane monooxygenase gene cluster sequence would help to understand its catalytic mechanism and enhance the application in pollutants biodegradation. The methanotrophs was enriched and isolated with methane as the sole carbon source in the nitrate mineral salt medium. Then, five chlorinated hydrocarbons were selected as cometabolic substrates to study the biodegradation. The phylogenetic tree of 16S rDNA using MEGE5.05 software was constructed to identify the methanotroph strain. The pmoCAB gene cluster encoding particulate methane monooxygenase (pMMO) was amplified by semi-nested PCR in segments. ExPASy was performed to analyze theoretical molecular weight of the three pMMO subunits. As a result, a strain of methanotroph was isolated. The phylogenetic analysis indicated that the strain belongs to a species of Methylocystis, and it was named as Methylocystis sp. JTC3. The degradation rate of trichloroethylene (TCE) reached 93.79% when its initial concentration was 15.64 μmol/L after 5 days. We obtained the pmoCAB gene cluster of 3 227 bp including pmoC gene of 771 bp, pmoA gene of 759 bp, pmoB gene of 1 260 bp and two noncoding sequences in the middle by semi-nested PCR, T-A cloning and sequencing. The theoretical molecular weight of their corresponding gamma, beta and alpha subunit were 29.1 kDa, 28.6 kDa and 45.6 kDa respectively analyzed using ExPASy tool. The pmoCAB gene cluster of JTC3 was highly identical with that of Methylocystis sp. strain M analyzed by Blast, and pmoA sequences is more conservative than pmoC and pmoB. Finally, Methylocystis sp. JTC3 could degrade TCE efficiently. And the detailed analysis of pmoCAB from Methylocystis sp. JTC3 laid a solid foundation to further study its active sites features and its selectivity to chlorinated hydrocarbon.
Methylocystaceae ; classification ; metabolism ; Multigene Family ; Oxygenases ; genetics ; Phylogeny ; Polymerase Chain Reaction ; RNA, Ribosomal, 16S ; genetics ; Sequence Analysis, DNA ; Trichloroethylene ; metabolism