Influence of microbial inoculation site on trichloroethylene degradation in electrokinetic-enhanced bioremediation of low-permeability soils.

The integration of electrokinetic and bioremediation (EK-BIO) represents an innovative approach for addressing trichloroethylene (TCE) contamination in low-permeability soil. However, there remains a knowledge gap in the impact of the inoculation approach on TCE dechlorination and the microbial response with the presence of co-existing substances. In this study, four 1-dimensional columns were constructed with different inoculation treatments. Monitoring the operation conditions revealed that a stabilization period (∼40 days) was required to reduce voltage fluctuation. The group with inoculation into the soil middle (Group B) exhibited the highest TCE dechlorination efficiency, achieving a TCE removal rate of 84%, which was 1.1-3.2 fold higher compared to the others. Among degraded products in Group B, 39% was ethylene. The physicochemical properties of the post-soil at different regions illustrated that dechlorination coincided with the Fe(III) and SO42- reduction, meaning that the EK-BIO system promoted the formation of a reducing environment. Microbial community analysis demonstrated that Dehalococcoides was only detected in the treatment of injection at soil middle or near the cathode, with abundance enriched by 2.1%-7.2%. The principal components analysis indicated that the inoculation approach significantly affected the evolution of functional bacteria. Quantitative polymerase chain reaction (qPCR) analysis demonstrated that Group B exhibited at least 2.8 and 4.2-fold higher copies of functional genes (tceA, vcrA) than those of other groups. In conclusion, this study contributes to the development of effective strategies for enhancing TCE biodechlorination in the EK-BIO system, which is particularly beneficial for the remediation of low-permeability soils.

Bioreduction of chromate in a syngas-based membrane biofilm reactor.

This study leveraged synthesis gas (syngas), a renewable resource attainable through the gasification of biowaste, to achieve efficient chromate removal from water. To enhance syngas transfer efficiency, a membrane biofilm reactor (MBfR) was employed. Long-term reactor operation showed a stable and high-level chromate removal efficiency > 95%, yielding harmless Cr(III) precipitates, as visualised by scanning electron microscopy and energy dispersive X-ray analysis. Corresponding to the short hydraulic retention time of 0.25 days, a high chromate removal rate of 80 µmol/L/d was attained. In addition to chromate reduction, in situ production of volatile fatty acids (VFAs) by gas fermentation was observed. Three sets of in situ batch tests and two groups of ex situ batch tests jointly unravelled the mechanisms, showing that biological chromate reduction was primarily driven by VFAs produced from in situ syngas fermentation, whereas hydrogen originally present in the syngas played a minor role. 16 S rRNA gene amplicon sequencing has confirmed the enrichment of syngas-fermenting bacteria (such as Sporomusa), who performed in situ gas fermentation leading to the synthesis of VFAs, and organics-utilising bacteria (such as Aquitalea), who utilised VFAs to drive chromate reduction. These findings, combined with batch assays, elucidate the pathways orchestrating synergistic interactions between fermentative microbial cohorts and chromate-reducing microorganisms. The findings facilitate the development of cost-effective strategies for groundwater and drinking water remediation and present an alternative application scenario for syngas.

Biological bromate reduction coupled with in situ gas fermentation in H2/CO2-based membrane biofilm reactor.

Bromate, a carcinogenic contaminant generated in water disinfection, presents a pressing environmental concern. While biological bromate reduction is an effective remediation approach, its implementation often necessitates the addition of organics, incurring high operational costs. This study demonstrated the efficient biological bromate reduction using H2/CO2 mixture as the feedstock. A membrane biofilm reactor (MBfR) was used for the efficient delivery of gases. Long-term reactor operation showed a high-level bromate removal efficiency of above 95 %, yielding harmless bromide as the final product. Corresponding to the short hydraulic retention time of 0.25 d, a high bromate removal rate of 4 mg Br/L/d was achieved. During the long-term operation, in situ production of volatile fatty acids (VFAs) by gas fermentation was observed, which can be regulated by controlling the gas flow. Three sets of in situ batch tests and two groups of ex situ batch tests jointly unravelled the mechanisms underpinning the efficient bromate removal, showing that the microbial bromate reduction was primarily driven by the VFAs produced from in situ gas fermentation. Microbial community analysis showed an increased abundance of Bacteroidota group from 4.0 % to 18.5 %, which is capable of performing syngas fermentation, and the presence of heterotrophic denitrifiers (e.g., Thauera and Brachymonas), which are known to perform bromate reduction. Together these results for the first time demonstrated the feasibility of using H2/CO2 mixture for bromate removal coupled with in situ VFAs production. The findings can facilitate the development of cost-effective strategies for groundwater and drinking water remediation.

Enzyme-induced reactive oxygen species trigger oxidative degradation of sulfamethoxazole within a methanotrophic biofilm.

Although microorganisms carrying copper-containing membrane-bound monooxygenase (CuMMOs), such as particulate methane monooxygenase (pMMO) and ammonia monooxygenase (AMO), have been extensively documented for their capability to degrade organic micropollutants (OMPs), the underlying reactive mechanism remains elusive. In this study, we for the first time demonstrate biogenic reactive oxygen species (ROS) play important roles in the degradation of sulfamethoxazole (SMX), a representative OMP, within a methane-fed biofilm. Highly-efficient and consistent SMX biodegradation was achieved in a CH4-based membrane biofilm reactor (MBfR), manifesting a remarkable SMX removal rate of 1210.6 ± 39.0 µg·L-1·d-1. Enzyme inhibition and ROS clearance experiments confirmed the significant contribution of ROS, which were generated through the catalytic reaction of pMMO and AMO enzymes, in facilitating SMX degradation. Through a combination of density functional theory (DFT) calculations, electron paramagnetic resonance (EPR) analysis, and transformation product detection, we elucidated that the ROS primarily targeted the aniline group in the SMX molecule, inducing the formation of aromatic radicals and its progressive mineralization. In contrast, the isoxazole-ring was not susceptible to electrophilic ROS attacks, leading to accumulation of 3-amino-5-methylisoxazole (3A5MI). Furthermore, microbiological analysis suggested Methylosarcina (a methanotroph) and Candidatus Nitrosotenuis (an ammonia-oxidizing archaea) collaborated as the SMX degraders, who carried highly conserved and expressed CuMMOs (pMMO and AMO) for ROS generation, thereby triggering the oxidative degradation of SMX. This study deciphers SMX biodegradation through a fresh perspective of free radical chemistry, and concurrently providing a theoretical framework for the advancement of environmental biotechnologies aimed at OMP removal.

Nitrate-driven anaerobic oxidation of ethane and butane by bacteria.

The short-chain gaseous alkanes (ethane, propane, and butane; SCGAs) are important components of natural gas, yet their fate in environmental systems is poorly understood. Microbially mediated anaerobic oxidation of SCGAs coupled to nitrate reduction has been demonstrated for propane, but is yet to be shown for ethane or butane-despite being energetically feasible. Here we report two independent bacterial enrichments performing anaerobic ethane and butane oxidation, respectively, coupled to nitrate reduction to dinitrogen gas and ammonium. Isotopic 13C- and 15N-labelling experiments, mass and electron balance tests, and metabolite and meta-omics analyses collectively reveal that the recently described propane-oxidizing "Candidatus Alkanivorans nitratireducens" was also responsible for nitrate-dependent anaerobic oxidation of the SCGAs in both these enrichments. The complete genome of this species encodes alkylsuccinate synthase genes for the activation of ethane/butane via fumarate addition. Further substrate range tests confirm that "Ca. A. nitratireducens" is metabolically versatile, being able to degrade ethane, propane, and butane under anoxic conditions. Moreover, our study proves nitrate as an additional electron sink for ethane and butane in anaerobic environments, and for the first time demonstrates the use of the fumarate addition pathway in anaerobic ethane oxidation. These findings contribute to our understanding of microbial metabolism of SCGAs in anaerobic environments.

Methane Oxidation Coupled to Selenate Reduction in a Membrane Bioreactor under Oxygen-Limiting Conditions.

Microbial methane oxidation coupled to a selenate reduction process has been proposed as a promising solution to treat contaminated water, yet the underlying microbial mechanisms are still unclear. In this study, a novel methane-based membrane bioreactor system integrating hollow fiber membranes for efficient gas delivery and ultrafiltration membranes for biomass retention was established to successfully enrich abundant suspended cultures able to perform methane-dependent selenate reduction under oxygen-limiting conditions. The microbial metabolic mechanisms were then systematically investigated through a combination of short-term batch tests, DNA-based stable isotope probing (SIP) microcosm incubation, and high-throughput sequencing analyses of 16S rRNA gene and functional genes (pmoA and narG). We confirmed that the methane-supported selenate reduction process was accomplished by a microbial consortia consisting of type-II aerobic methanotrophs and several heterotrophic selenate reducers. The mass balance and validation tests on possible intermediates suggested that methane was partially oxidized into acetate under oxygen-limiting conditions, which was consumed as a carbon source for selenate-reducing bacteria. High-throughput 16S rRNA gene sequencing, DNA-SIP incubation with 13CH4, and subsequent functional gene (pmoA and narG) sequencing results collectively proved that Methylocystis actively executed partial methane oxidation and Acidovorax and Denitratisoma were dominant selenate-reducing bacteria, thus forming a syntrophic partnership to drive selenate reduction. The findings not only advance our understanding of methane oxidation coupled to selenate reduction under oxygen-limiting conditions but also offer useful information on developing methane-based biotechnology for bioremediation of selenate-contaminated water.

Primary versus salvage intratympanic steroid treatment for idiopathic sudden sensorineural hearing loss.

Objective: The objective of this research is to compare primary and salvage intratympanic (IT) steroid treatments in terms of hearing outcomes in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). Methods: The patients were randomized into two (primary and salvage) groups. Both groups received systemic steroid treatment for 2 weeks. The primary group also received IT dexamethasone injection three times during the treatment period, whereas the salvage group received IT dexamethasone injection only if no or slight recovery was noted at the 2-week follow-up. If needed, salvage steroid injection was administered three times during the following 2 weeks. Hearing recovery was analyzed according to the modified American Academy of Otolaryngology-Head and Neck Surgery criteria. Results: The degrees of hearing improvement at the 3-month follow-up were similar in the two groups. Compared with baseline, the pure-tone average values and speech discrimination scores improved by 38.45 ± 21.95 dB HL and 34.32% ± 30.55%, respectively, in the primary group and 36.80 ± 22.33 dB HL and 31.87% ± 27.88%, respectively, in the salvage group (p = .762 and .659, respectively). In addition, the complete or partial hearing recovery rates were also similar in the primary and salvage groups (67.7% vs. 73.3%, respectively; p = .780). In the salvage group, 18 patients required no IT steroid injection because they recovered after systemic steroid treatment. Conclusion: Primary and salvage IT steroid treatments for ISSNHL led to similar outcomes. In summary, salvage IT steroid injection is recommended for patients with ISSNHL patients to prevent unnecessary IT injection. Level of evidence: 2.

Heart Rate Estimation from Facial Image Sequences of a Dual-Modality RGB-NIR Camera.

This paper presents an RGB-NIR (Near Infrared) dual-modality technique to analyze the remote photoplethysmogram (rPPG) signal and hence estimate the heart rate (in beats per minute), from a facial image sequence. Our main innovative contribution is the introduction of several denoising techniques such as Modified Amplitude Selective Filtering (MASF), Wavelet Decomposition (WD), and Robust Principal Component Analysis (RPCA), which take advantage of RGB and NIR band characteristics to uncover the rPPG signals effectively through this Independent Component Analysis (ICA)-based algorithm. Two datasets, of which one is the public PURE dataset and the other is the CCUHR dataset built with a popular Intel RealSense D435 RGB-D camera, are adopted in our experiments. Facial video sequences in the two datasets are diverse in nature with normal brightness, under-illumination (i.e., dark), and facial motion. Experimental results show that the proposed method has reached competitive accuracies among the state-of-the-art methods even at a shorter video length. For example, our method achieves MAE = 4.45 bpm (beats per minute) and RMSE = 6.18 bpm for RGB-NIR videos of 10 and 20 s in the CCUHR dataset and MAE = 3.24 bpm and RMSE = 4.1 bpm for RGB videos of 60-s in the PURE dataset. Our system has the advantages of accessible and affordable hardware, simple and fast computations, and wide realistic applications.

Microbial nitrate reduction in propane- or butane-based membrane biofilm reactors under oxygen-limiting conditions.

Nitrate contamination has been commonly detected in water environments and poses serious hazards to human health. Previously methane was proposed as a promising electron donor to remove nitrate from contaminated water. Compared with pure methane, natural gas, which not only contains methane but also other short chain gaseous alkanes (SCGAs), is less expensive and more widely available, representing a more attractive electron source for removing oxidized contaminants. However, it remains unknown if these SCGAs can be utilized as electron donors for nitrate reduction. Here, two lab-scale membrane biofilm reactors (MBfRs) separately supplied with propane and butane were operated under oxygen-limiting conditions to test its feasibility of microbial nitrate reduction. Long-term performance suggested nitrate could be continuously removed at a rate of ∼40-50 mg N/L/d using propane/butane as electron donors. In the absence of propane/butane, nitrate removal rates significantly decreased both in the long-term operation (∼2-10 and ∼4-9 mg N/L/d for propane- and butane-based MBfRs, respectively) and batch tests, indicating nitrate bio-reduction was driven by propane/butane. The consumption rates of nitrate and propane/butane dramatically decreased under anaerobic conditions, but recovered after resupplying limited oxygen, suggesting oxygen was an essential triggering factor for propane/butane-based nitrate reduction. High-throughput sequencing targeting 16S rRNA, bmoX and narG genes indicated Mycobacterium/Rhodococcus/Thauera were the potential microorganisms oxidizing propane/butane, while various denitrifiers (e.g. Dechloromonas, Denitratisoma, Zoogloea, Acidovorax, Variovorax, Pseudogulbenkiania and Rhodanobacter) might perform nitrate reduction in the biofilms. Our findings provide evidence to link SCGA oxidation with nitrate reduction under oxygen-limiting conditions and may ultimately facilitate the design of cost-effective techniques for ex-situ groundwater remediation using natural gas.

The efficacy and safety of cupping as complementary and alternative therapy for metabolic syndrome: A systematic review and meta-analysis.

INTRODUCTION: This systematic review and meta-analysis aimed to assess the efficacy and safety of cupping therapy in patients with metabolic syndrome (MetS). METHODS: This systematic review focused on patients with MetS and included randomized controlled trials (RCTs) that compared the effects of cupping therapy with control groups. A total of 12 electronic databases were searched from inception until February 03, 2023. The main outcome after the meta-analysis was waist circumference; the others included anthropometric variables, blood pressure, lipid profile, fasting blood glucose level, and high-sensitivity C-reactive protein level. The incidence of adverse events and the follow-up courses were also evaluated. Risk of bias (ROB) was evaluated using ROB 2.0 from the Cochrane Handbook. RESULTS: This systematic review included five studies involving 489 patients. Some risks of bias were also identified. The meta-analysis revealed a statistically significance in waist circumference (MD = -6.07, 95% CI: -8.44 to -3.71, P < .001, I2 = 61%, τ2 = 3.4), body weight (MD = -2.46, 95% CI: -4.25 to -0.68, P = .007, I2 = 0%, τ2 = 0) and body mass index (MD = -1.26, 95% CI: -2.11 to -0.40, P = .004, I2 = 0%, τ2 = 0) between the cupping therapy and control groups. However, there were no significant results in total fat percentage and blood pressure values. Regarding biochemical markers, cupping significantly lowered the concentration of low-density lipoprotein cholesterol (MD = -3.98, 95% CI: -6.99 to -0.96, P = .010, I2 = 0%, τ2 = 0) but had no significant effect on total cholesterol, triglyceride, high-density lipoprotein cholesterol, fasting blood glucose, and high-sensitivity C-reactive protein. 3 RCTs reported no adverse events. CONCLUSIONS: Despite some ROB and low to substantial heterogeneity of the included studies, cupping therapy can be considered a safe and effective complementary intervention for reducing waist circumference, body weight, body mass index, and low-density lipoprotein cholesterol in patients with MetS. In the future, well-designed, high-quality, rigorous methodology, and long-term RCTs in this population are required to assess the efficacy and safety of cupping therapy.

Heterotrophic denitrification: An overlooked factor that contributes to nitrogen removal in n-DAMO mixed culture.

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) has been recognized as a sustainable process for simultaneous removal of nitrogen and methane. The metabolisms of denitrifying anaerobic methanotrophs, including Candidatus Methanoperedens and Candidatus Methylomirabilis, have been well studied. However, potential roles of heterotrophs co-existing with these anaerobic methanotrophs are generally overlooked. In this study, we pulse-fed methane and nitrate into an anaerobic laboratory sequencing batch bioreactor and enriched a mixed culture with stable nitrate removal rate (NRR) of ∼28 mg NO3--N L-1 d-1. Microbial community analysis indicates abundant heterotrophs, e.g., Arenimonas (5.3%-18.9%) and Fimbriimonadales ATM1 (6.4%), were enriched together with denitrifying anaerobic methanotrophs Ca. Methanoperedens (10.8%-13.2%) and Ca. Methylomirabilis (27.4%-34.3%). The results of metagenomics and batch tests suggested that the denitrifying anaerobic methanotrophs were capable of generating methane-derived intermediates (i.e., formate and acetate), which were employed by non-methanotrophic heterotrophs for denitrification and biomass growth. These findings offer new insights into the roles of heterotrophs in n-DAMO mixed culture, which may help to optimize n-DAMO process for nitrogen removal from wastewater.

Application of acupuncture in the emergency department for patients with ileus: A pilot prospective cohort clinical study.

Acupuncture can be conveniently used for pain control in patients with a variety of conditions, and it has obvious effects on various acute pains. In 2018, we implemented a program for emergency treatment with Chinese medicine to promote the integration of Chinese and Western medicine at the Emergency Department (ED). Ileus is a common cause of abdominal pain among patients in the ED, and it is an indication for emergency treatment with Chinese medicine. This study investigated the efficacy of acupuncture as a traditional Chinese medicine (TCM)-based treatment method for the treatment of patients with ileus in the ED. We analyzed data of patients with ileus, who visited ED between January and December 2019, and compared the length of ED stay between the Western medicine group and the Western medicine plus acupuncture group. Furthermore, pain intensity was measured by a visual analogue scale before and after acupuncture. We found that the length of ED stay was 10.8 hours lesser in the Western medicine plus acupuncture group than in the Western medicine group (P = .04), and the visual analogue scale score decreased by 2.0 on average from before to after acupuncture treatment (P = .02). Acupuncture treatment was effective and rapid in relieving the symptoms and discomfort in patients with ileus and in reducing their length of stay in the ED.

Impact of AIS 2015 versus 1998 on injury severity scoring and mortality prediction - single centre retrospective comparison study.

BACKGROUND: A key component of trauma system evaluation is the Injury Severity Score (ISS). The ISS is dependent on the AIS, and as AIS versions are updated this effects the number of patients within a health system which are considered severely injured (ISS >15). This study aims to analyse the changes comparing AIS1998 and AIS2015, and its impact on injury severity scoring and survival prediction model in a major trauma centre. METHODS: This retrospective study reviewed all blunt trauma admissions from 1 January 2020 to 31 December 2020 from the trauma registry of Prince of Wales Hospital, Hong Kong. Patients were manually double coded with AIS1998 and AIS2015 by the same experienced trauma nurse who have completed both AIS 1998 and AIS 2015 Courses. AIS patterns and Injury Severity Scores (ISS) derived from AIS 1998 and 2015 were compared using the Wilcoxon Signed Rank Test. The area under the receiving operator curve (AUROC) was compared based on the Trauma and Injury Severity Score (TRISS) model using AIS 1998 and AIS 2015. RESULTS: 739 patients were included. There were 34 deaths within 30 days (30-day mortality rate 4.6%). Patients coded with AIS2015 compared with AIS1998 had significant reductions in the classification of serious, severe and critical categories of AIS, with a substantial increase in the mild and moderate categories. The largest reduction was observed in the head and neck region (Z = -11.018, p < 0.001), followed by the chest (Z = -6.110, p < 0.001), abdomen (Z = -4.221, p < 0.001) and extremity regions (Z = -4.252, p < 0.001). There was a 27% reduction in number of cases with ISS >15 in AIS2015 compared with AIS1998. Rates of 30-day mortality, ICU admission, emergency operation and trauma team activation of ISS > 15 using AIS 1998 were similar to the cut off for New Injury Severity Score (NISS) >12 using AIS 2015. The AUROC from the TRISS (AIS2015) was 0.942, and not different from the AUROC for TRISS (AIS1998) of 0.936. The sensitivity and specificity were 93.9% and 82.1% for TRISS (AIS2015), and 93.9% and 76.0% for TRISS (AIS1998). CONCLUSION: Trauma centres should be aware of the impact of the AIS2015 update on the benchmarking of trauma care, and consider the need for updating the ISS cut off for major trauma definitions.

The flavonoid corylin exhibits lifespan extension properties in mouse.

In the long history of traditional Chinese medicine, single herbs and complex formulas have been suggested to increase lifespan. However, the identification of single molecules responsible for lifespan extension has been challenging. Here, we collected a list of traditional Chinese medicines with potential longevity properties from pharmacopeias. By utilizing the mother enrichment program, we systematically screened these traditional Chinese medicines and identified a single herb, Psoralea corylifolia, that increases lifespan in Saccharomyces cerevisiae. Next, twenty-two pure compounds were isolated from Psoralea corylifolia. One of the compounds, corylin, was found to extend the replicative lifespan in yeast by targeting the Gtr1 protein. In human umbilical vein endothelial cells, RNA sequencing data showed that corylin ameliorates cellular senescence. We also examined an in vivo mammalian model, and found that corylin extends lifespan in mice fed a high-fat diet. Taken together, these findings suggest that corylin may promote longevity.

Copper stimulation on methane-supported perchlorate reduction in a membrane biofilm reactor.

The present study demonstrated that the perchlorate reduction rate in a methane-based membrane biofilm reactor was significantly enhanced from 14.4 to 25.6 mg-Cl/L/d by increasing copper concentration in the feeding medium from 1 to 10 µM, indicating a stimulatory effect of copper on the methane-supported perchlorate reduction process. Batch tests further confirmed that the increased copper concentration enhanced both methane oxidation and perchlorate reduction rates, which was supported by an increasing trend of functional genes (pmoA for methanotrophs and pcrA for specific perchlorate reducers) abundances through quantitative polymerase chain reaction (qPCR). Both 16S rRNA gene sequencing and functional genes (pmoA and pcrA) sequencing jointly revealed that the biofilm supplied with a higher copper concentration exhibited a more diverse microbial community. The methane-supported perchlorate reduction was accomplished through a synergistic association of methanotrophs (Methylocystis, Methylomonas, and Methylocystaceae) and perchlorate reducers (Dechloromonas, Azospira, Magnetospirillum, and Denitratisoma). Acetate may function as the key syntrophic linkage between methanotrophs and perchlorate reducers. It was proposed that the increased copper concentration improved the activity of particulate methane monooxygenase (pMMO) for methane oxidation or promoted the biosynthesis of intracellular carbon storage compounds polyhydroxybutyrate (PHB) in methanotrophs for generating more acetate available for perchlorate reduction.

RISC II is superior to TRISS in predicting 30-day mortality in blunt major trauma patients in Hong Kong.

PURPOSE: Hong Kong (HK) trauma registries have been using the Trauma and Injury Severity Score (TRISS) for audit and benchmarking since their introduction in 2000. We compare the mortality prediction model using TRISS and Revised Injury Severity Classification, version II (RISC II) for trauma centre patients in HK. METHODS: This was a retrospective cohort study with all five trauma centres in HK. Adult trauma patients with Injury Severity Score (ISS) > 15 suffering from blunt injuries from January 2013 to December 2015 were included. TRISS models using the US and local coefficients were compared with the RISC II model. The primary outcome was 30-day mortality and the area under the receiver operating characteristic curve (AUC) for tested models. RESULTS: 1840 patients were included, of whom 1236/1840 (67%) were male. Median age was 59 years and median ISS was 25. Low falls were the most common mechanism of injury. The 30-day mortality was 23%. RISC II yielded a superior AUC of 0.896, compared with the TRISS models (MTOS: 0.848; PATOS: 0.839; HK: 0.858). Prespecified subgroup analyses showed that all the models performed worse for age ≥ 70, ASA ≥ III, and low falls. RISC II had a higher AUC compared with the TRISS models in all subgroups, although not statistically significant. CONCLUSION: RISC II was superior to TRISS in predicting the 30-day mortality for Hong Kong adult blunt major trauma patients. RISC II may be useful when performing future audit or benchmarking exercises for trauma in Hong Kong.

Methane-dependent selenate reduction by a bacterial consortium.

Methanotrophic microorganisms play a critical role in controlling the flux of methane from natural sediments into the atmosphere. Methanotrophs have been shown to couple the oxidation of methane to the reduction of diverse electron acceptors (e.g., oxygen, sulfate, nitrate, and metal oxides), either independently or in consortia with other microbial partners. Although several studies have reported the phenomenon of methane oxidation linked to selenate reduction, neither the microorganisms involved nor the underlying trophic interaction has been clearly identified. Here, we provide the first detailed evidence for interspecies electron transfer between bacterial populations in a bioreactor community where the reduction of selenate is linked to methane oxidation. Metagenomic and metaproteomic analyses of the community revealed a novel species of Methylocystis as the most abundant methanotroph, which actively expressed proteins for oxygen-dependent methane oxidation and fermentation pathways, but lacked the genetic potential for selenate reduction. Pseudoxanthomonas, Piscinibacter, and Rhodocyclaceae populations appeared to be responsible for the observed selenate reduction using proteins initially annotated as periplasmic nitrate reductases, with fermentation by-products released by the methanotrophs as electron donors. The ability for the annotated nitrate reductases to reduce selenate was confirmed by gene knockout studies in an isolate of Pseudoxanthomonas. Overall, this study provides novel insights into the metabolic flexibility of the aerobic methanotrophs that likely allows them to thrive across natural oxygen gradients, and highlights the potential role for similar microbial consortia in linking methane and other biogeochemical cycles in environments where oxygen is limited.

Cross-feeding interactions in short chain gaseous alkane-driven perchlorate and selenate reduction.

Short chain gaseous alkanes (SCGAs) mainly consist of methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10). The first three SCGAs have been shown to remove perchlorate (ClO4-) and selenate (SeO42-), yet it is unknown whether C4H10 is available to reduce these contaminants. This study demonstrated that C4H10 fed biofilms were capable of reducing ClO4- and SeO42- to chloride (Cl-) and elemental selenium (Se0), respectively, by employing two independent membrane biofilms reactors (MBfRs). Batch tests showed that C4H10 and oxygen fed biofilms had much higher ClO4- and SeO42- reduction rates and enhanced expression levels of bmoX and pcrA than that without C4H10 or O2. Polyhydroxyalkanoates (PHA) accumulated in the biofilms when C4H10 was supplied, and they decomposed for driving ClO4- and SeO42- reduction when C4H10 was absent. Moreover, we revisited the literature and found that a cross-feeding pathway seems to be universal in microaerobic SCGA-driven perchlorate and selenate reduction processes. In the ClO4--reducing MBfRs, Mycobacterium primarily conducts C2H6 and C3H8 oxidation in synergy with Dechloromonas who performs perchlorate reduction, while both Mycobacterium and Rhodococcus carried out C4H10 oxidation with perchlorate-respiring Azospira as the partner. In the SeO42--reducing MBfRs, Mycobacterium oxidized C2H6 solely or oxidized C3H8 jointly with Rhodococcus, while Burkholderiaceae likely acted as the selenate-reducing bacterium. When C4H10 was supplied as the electron donor, both Mycobacterium and Rhodococcus conducted C4H10 oxidation in synergy with unknow selenate-reducing bacterium. Collectively, we confirm that from CH4 to C4H10, all SCGAs could be utilized as electron donors for bio-reduction process. These findings offer insights into SCGA-driven bio-reduction processes, and are helpful in establishing SCGA-based technologies for groundwater remediation.