Quinolone antibiotics stimulate bacterial mercury methylation by Geobacter metallireducens GS-15.

Bacterial mercury (Hg) methylation is critical for bioremediating Hg pollution, but the impact of emerging antibiotics on this process has rarely been reported. This study innovatively investigated the interactions between Hg-methylating bacteria of Geobacter metallireducens GS-15 and two quinolone antibiotics: lomefloxacin (LOM) and ciprofloxacin (CIP) at 5 µg/L. Short-term LOM exposure increased methylmercury (MeHg) yield by 36 % compared to antibiotic-free conditions, caused by hormesis to alter bioactivities of single GS-15 cells. Long-term CIP exposure led to more antibiotic resistance and mercury tolerance in GS-15 cells, doubling MeHg productivity and significantly increasing expression of Hg methylation (hgcA by 95 folds) and antibiotic resistance (gyrA by 54 folds) genes, while mercury resistance gene merA only increased by 2.5 folds than without selective pressure. These results suggest quinolone antibiotics at environmentally contaminated concentrations stimulate bacterial Hg methylation to form highly toxic MeHg, raising considerable concern for the Hg-antibiotic complex in contaminated environments.

Bacterial mercury methylation modulated by vitamin B9: An overlooked pathway leads to increased environmental risks.

There has been a serious health and environmental concern in conversion of inorganic mercury (Hg) to the neurotoxin, methylmercury (MeHg) by anaerobic microbes, while very little is known about the potential role of vitamin B9 (VB9) regulator in the biochemical generation of MeHg. This study innovatively investigated bacterial Hg methylation by Geobacter sulfurreducens PCA in the presence of VB9 under two existing scenarios. In the low-complexing scenario, the bacterial MeHg yield reached 68 % higher than that without VB9 within 72 h, which was attributed to free VB9-protected PCA cells relieving oxidative stress, as manifested by the increased expression of Hg methylation gene (hgcAB cluster by 19-48 %). The high-complexing scenario emphasized the intracellular Hg accumulation (38-45 %) after 12 h, as indicated by the increased expression of outer membrane protein-related and mercuric reductase-encoding genes, indicating the inefficient bioavailability of Hg due to a gradual shift from Hg reduction toward Hg0 re-oxidation controlled by competitive ligand exchange. These results suggested that VB9 application significantly raised the potential for bacterial Hg methylation and cellular accumulation, thus proposing insights into the biochemical behaviors of hazardous Hg in farming environments where vulnerable organisms are more possibly co-exposed to higher levels of Hg and VB9.

An integrated meta-omics approach reveals the different response mechanisms of two anammox bacteria towards fluoroquinolone antibiotics.

The emerging fluoroquinolone antibiotics (FQs) are highly influential in nitrogen removal from livestock wastewater. However, beyond the capability of nitrogen removal, little is known about the molecular mechanisms (e.g., shift of core metabolism and energy allocation) of different anaerobic ammonium-oxidizing bacteria (AnAOB) under continuous FQ stress. This study investigated the effects of ciprofloxacin, ofloxacin and their mixture at concentrations detected in livestock wastewater on two key anammox species in membrane bioreactors. It was found 20 µg/L FQs promoted nitrogen removal efficiency and community stability, and42-51 % of FQs were removed simultaneously. Integrated meta-omics analysis revealed varied gene expression patterns between the two dominant AnAOB, Candidatus Brocadia sapporoensis (B AnAOB) and Candidatus Kuenenia stuttgartiensis (K AnAOB). The nitrogen metabolic processes were bolstered in B AnAOB, while those involved in anammox pathway of K AnAOB were inhibited. This difference was tentatively attributed to the up-regulation of reactive oxygen species scavenger genes (ccp and dxf) and FQ resistance gene (qnrB72) in B AnAOB. Importantly, most enhanced core biosynthesis/metabolism of AnAOB and close cross-feeding with accompanying bacteria were also likely to contribute to their higher levels of biomass yield and metabolism activity under FQ stress. This finding suggests that B AnAOB has the advantage of higher nitrogen metabolism capacity over K AnAOB in livestock wastewater containing FQs, which is helpful for efficient and stable nitrogen removal by the functional anammox species.

Molecular insights into enhanced nitrogen removal induced by trace fluoroquinolone antibiotics in an anammox system.

It has been widely reported that fluoroquinolones (FQs) can affect the anaerobic ammonium oxidization (anammox) microorganisms, which interferes with the performance of nitrogen removal from wastewater. However, the metabolic mechanism of anammox microorganisms responding to FQs has rarely been explored. In this study, it was found that 20 µg/L FQs promoted the nitrogen removal performance of anammox microorganisms in batch exposure assays, and 36-51% of FQs were removed simultaneously. Combined metabolomics and genome-resolved metagenomic analysis revealed up-regulated carbon fixation in anammox bacteria (AnAOB), while purine and pyrimidine metabolism, protein generation and transmembrane transport were enhanced in AnAOB and symbiotic bacteria by 20 µg/L FQs. Consequently, hydrazine dehydrogenation, nitrite reduction, and ammonium assimilation were bolstered, improving the nitrogen removal efficiency of the anammox system. These results revealed the potential roles of specific microorganisms in response to emerging FQs and provided further information for practical application of anammox technology in wastewater treatment.

Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium.

Bacteria are key denitrifiers in the reduction of nitrate (NO3 --N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO3 --N in wastewater. Efficient removal of NO3 --N and recovery of biomass nitrogen were achieved. Up to 99% of NO3 --N was removed without accumulation of nitrite and N2O, consuming CO2 of 3.25 mol for each mole of NO3 --N removed. The overall removal rate of NO3 --N reached 1.1 mg L-1 h-1 with a biomass content of approximately 0.71 g L-1 within 72 h. TH20 participated in NO3 --N assimilation and aerobic denitrification. Results from 15N-labeled-nitrate test indicated that removed NO3 --N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO2 and N2O emissions.

Spatiotemporal distribution, source apportionment and risk assessment of typical hormones and phenolic endocrine disrupting chemicals in environmental and biological samples from the mariculture areas in the Pearl River Delta, China.

The present work studied the levels, distribution, potential sources, ecological and human health risks of typical hormones and phenolic endocrine disrupting chemicals (EDCs) in the mariculture areas of the Pearl River Delta (PRD), China. The environmental levels of 11 hormones (6 estrogens, 4 progestogens, and 1 androgen) and 2 phenolic EDCs were quantified in various matrices including water, sediment, cultured fish and shellfish. Ultrahigh performance liquid chromatography-triple quadrupole tandem mass spectrometry analyses showed that all the 13 target compounds were detected in biotic samples, whereas 10 were detected in water and sediment, respectively. The total concentrations ranged from 35.06-364.53 ng/L in water and 6.31-29.30 ng/g in sediment, respectively. The average contaminant levels in shellfish (Ostrea gigas, Mytilus edulis and Mimachlamys nobilis) were significantly higher than those in fish (Culter alburnus, Ephippus orbis and Ephippus orbis). Source apportionment revealed that the pollution of hormones and phenolic EDCs in PRD mariculture areas was resulted from the combination of coastal anthropogenic discharges and mariculture activities. The hazard quotient values of the contaminants were all less than 1, implying no immediate human health risk. Overall, the present study is of great significance for scientific mariculture management, land-based pollution control, ecosystem protection, and safeguarding human health.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics.

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Highly efficient ammonium removal through nitrogen assimilation by a hydrogen-oxidizing bacterium, Ideonella sp. TH17.

Ideonella sp. TH17, an autotrophic hydrogen-oxidizing bacterium (HOB), was successfully enriched and isolated from activated sludge in a domestic wastewater treatment plant (WWTP). Batch experiments were conducted to identify the cell growth and ammonium (NH4+-N) removal, and to verify the pathways of nitrogen utilization under different conditions. At a representative NH4+-N concentration of 100 mg/L in domestic wastewater, it was the first time that a HOB strain achieved a nearly 100% ammonium removal. More than 90% of NH4+-N was assimilated to biomass nitrogen by strain TH17. Only a little of N2 (<10% of initial NH4+-N) was detected without N2O emission in aerobic denitrification process. Autotrophic NH4+-N assimilation contributed predominantly to biomass nitrogen production, supplemented by assimilatory nitrate (NO3--N) reduction under aerobic conditions. A total of 17 amino acids, accounting for 54.25 ± 1.98% of the dry biomass, were detected in the bacterial biomass harvested at 72 h. These results demonstrated that the newly isolated strain TH17 was capable of removing NH4+-N and recovering nutrients from wastewater efficiently. A new solution was thus provided by this HOB strain for ammonium treatment in sustainable WWTPs of future.

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via. bioreduction followed by reoxidation.

This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation. Field tests (1383 days) at Oak Ridge, Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater. Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L. Aliquots of the bioreduced sediment were reoxidized with O2, H2O2, and NaNO3, respectively, over 285 days, resulting in aqueous U of 0.024, 1.58 and 14.4 mg/L at pH 6.30, 6.63 and 7.62, respectively. The source- and the three reoxidized sediments showed different desorption and adsorption behaviors of U, but all fit a Freundlich model. The adsorption capacities increased sharply at pH 4.5 to 5.5, plateaued at pH 5.5 to 7.0, then decreased sharply as pH increased from 7.0 to 8.0. The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0. The NO3--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0. The pH-dependent adsorption onto Fe(III) oxides and formation of U coated particles and precipitates resulted in U sequestration, and bioreduction followed by reoxidation can enhance the U sequestration in sediment.

Mercury methylation by Geobacter metallireducens GS-15 in the presence of Skeletonema costatum.

In this study, bacterial mercury (Hg) methylation was investigated under the influence of red-tide algae of Skeletonema costatum (S. costatum). The distribution and speciation of total mercury (THg) and methylmercury (MeHg) were profiled by employing Geobacter metallireducens (G. metallireducens GS-15) as the methylating bacteria. G. metallireducens GS-15 showed different capabilities in methylating different inorganic forms of Hg(II) (HgCl2) and Hg(II)-Algae (HgCl2 captured by S. costatum) to MeHg. In the absence of S. costatum, a maximum methylation efficiency of 4.31 ±â€¯0.47% was achieved with Hg(II) of 1-100 µg L-1, while accelerated MeHg formation rate was detected at a higher initial Hg(II) concentration. In the presence of S. costatum, there were distinct changes in the distribution of THg and MeHg by altering the bioavailability of Hg(II) and Hg(II)-Algae. A larger proportion of THg tended to be retained by a higher algal biomass, resulting in decreased methylation efficiencies. The methylation efficiency of Hg(II) decreased from 3.01 ±â€¯0.10% to 1.01 ±â€¯0.01% with 10-mL and 250-mL algal media, and that of Hg(II)-Algae decreased from 0.83 ±â€¯0.13% to 0.22 ±â€¯0.01% with 10-mL and 250-mL Hg(II)-Algae media. Fourier transform infrared spectrometry, surface charge properties and elemental compositions of S. costatum were used to infer that amine, carboxyl and sulfonate functional groups were most likely to interact with Hg(II) through complexation and/or electrostatic attraction. These results suggest that red-tide algae may be an influencing factor on bacterial Hg methylation in eutrophic water bodies.

Identification of quorum sensing signal AHLs synthases in Candidatus Jettenia caeni and their roles in anammox activity.

Acyl-homoserine lactone (AHL)-based quorum sensing (QS) in the anaerobic ammonium oxidizing (anammox) consortia has attracted increasing attention. However, AHL synthase in anammox bacteria and the relationship between AHL synthetic genes and anammox activity are still not clear because anammox bacteria have not been isolated from the consortia. Two novel synthases of AHLs (JqsI-1 and JqsI-2), which are HdtS-type rather than the widely studied LuxI-type, were identified in anammox bacteria Candidatus Jettenia caeni and synthesized four AHLs. There was a correlation between AHL concentration, in situ transcriptional expression of the AHL synthase genes (jqsI-1 and jqsI-2) and genetic marker of anammox activity (hydrazine synthase gene, hzsA). And AHL add-back studies demonstrated that AHL influence the expression of hzsA to regulate anammox bacterial activity. This study provides insight into the QS communication pathway of anammox bacteria for wastewater treatment.

Pharmaceuticals and personal care products in water, sediments, aquatic organisms, and fish feeds in the Pearl River Delta: Occurrence, distribution, potential sources, and health risk assessment.

This study investigated the occurrence, distribution, and potential sources of 34 pharmaceuticals and personal care products (PPCPs) in water, sediments, aquatic organisms (fish and shellfish), and fish feeds from the mariculture areas of the Pearl River Delta (PRD). The health risk presented by this class of compounds was also assessed in relation to their intake via seafood consumption. Of the 34 PPCPs, a total of 9, 21, 14, and 28 PPCPs were detected in water, sediments, fish feeds, and aquatic organisms, respectively. Trimethoprim, norfloxacin, ofloxacin, and spectinomycin were detected in all matrices. The levels of PPCPs in water and sediment samples were relatively low. Spectinomycin, paracetamol, ciprofloxacin, norfloxacin, and ibuprofen were the most frequently detected PPCPs in feeds. Ibuprofen and ketoprofen were widely detected in aquatic organisms, with average concentrations of 562 and 267 ng/g wet weight, respectively. The residual levels of PPCPs in shellfish such as ME (mussel, Mytilus edulis) and OS (oyster, Ostrea gigas) were significantly higher (p < 0.05) than those in other species including CA (topmouth culter, Culter alburnus) and EO (orbfish, Ephippus orbis). Correlation analysis indicated that the medicated feeds were a potential source of PPCPs in the mariculture areas of the PRD, but other anthropogenic sources should not be ignored. Based on maximum residue limits and acceptable daily intake, the health risks presented to humans via seafood consumption are negligible. However, as multiple antibiotics were frequently detected in the mariculture environment, aquatic organisms, and feeds, the induction and dissemination of antimicrobial resistance associated with antibiotic usage in aquaculture would be of great concern. It is necessary to establish a centralized management system and control the use of veterinary drugs in mariculture to protect the aquaculture environment and ensure the safety of seafood.

Inhibitory effects of Skeletonema costatum on mercury methylation by Geobacter sulfurreducens PCA.

Algae and mercury (Hg) are ubiquitous in marine environments. In this study, we investigated the effects of a typical marine algae of diatom Skeletonema costatum on Hg methylation by an iron-reducing bacterium of Geobacter sulfurreducens (G. sulfurreducens) PCA. In the absence of Skeletonema costatum, the bacterial MeHg production rate maximized at 104.06 ±â€¯11.7 ng L-1 h-1 with a high Hg level, while the highest methylation efficiency was achieved at a low Hg concentration. The existence of Skeletonema costatum greatly inhibited the capability of G. sulfurreducens PCA to methylate Hg. With the increase in algal biomass, there was a significant mitigation of MeHg formation and Hg0 release, leaving a considerable proportion of immobilized Hg2+ species (up to 47%) associated with algal cell materials. These results suggest that marine algae are crucial in determining the bioavailability of Hg contaminants and the methylating potential of G. sulfurreducens PCA.

Toxicity assessment of copper by electrochemically active bacteria in wastewater.

A bioelectrochemical sensor (BES) was constructed for toxicity assessment of copper in contaminated domestic sewage. Electrochemically active bacteria (EAB), whose growth was supported by the bioenergy generated from an in situ metallurgical process, functioned as the sensing elements. The external resistance of metallurgical BES was optimized based on linear sweep voltammetry analysis. The stabilized BES was utilized to monitor the copper toxicity in real wastewater. During the less than 1-h sensing period, copper concentration ranging from 1 to 5 mg L-1 could be detected. A power output of around 100 Wh (kg Cu)-1 and metallic copper resource were obtained simultaneously. This study demonstrated that the highly active EAB species enriched in metallurgical BES could be a promising candidate for rapid and reliable evaluation of copper toxicity in real domestic wastewater.

Magnetic chitosan/sodium alginate gel bead as a novel composite adsorbent for Cu(II) removal from aqueous solution.

Using sodium alginate hydrogel as skeleton, in combination with chitosan and magnetic Fe3O4, a new type of magnetic chitosan/sodium alginate gel bead (MCSB) was prepared. Adsorptive removal of Cu(II) from aqueous solutions was studied by using the MCSB as a promising candidate in environmental application. Different kinetics and isotherm models were employed to investigate the adsorption process. Based on Fourier transform infrared spectroscopy, field-emission scanning electron microscope, CHNS/O elements analysis, vibration magnetometer, and various means of characterization, a comprehensive analysis of the adsorption mechanism was conducted. The MCSB had a good magnetic performance with a saturation magnetization of 12.5 emu/g. Elemental analysis proved that the addition of chitosan introduced a considerable amount of nitrogen-rich groups, contributing significantly to copper adsorption onto gel beads. The contact time necessary for adsorption was optimized at 120 min to achieve equilibrium. Experimental data showed that the adsorption process agreed well with the Langmuir isotherm model and the pseudo-second-order kinetics model. The theoretical maximum adsorption capacity of MCSB for Cu(II) could reach as high as 124.53 mg/g. In conclusion, the MCSB in this study is a novel and promising composite adsorbent, which can be applied for practical applications in due course.

Feeding and metabolism effects of three common microplastics on Tenebrio molitor L.

Mealworms from three different regions: Guangzhou, Tai'an and Shenzhen, were fed with three commonly used microplastics of polystyrene (PS), polyvinyl chloride (PVC) and low-density polyethylene (LDPE) for 1 month under favorable conditions, respectively. The survival rate and average weight of mealworms, the mass loss of microplastics and the production of frass were recorded every 4 days. Samples collected were characterized by X-ray diffraction, fourier transform infrared spectroscopy, thermogravimetric analyzer and gel permeation chromatography. The results showed that mealworms from Tai'an and Shenzhen could effectively metabolize the whole microplastics tested, while those from Guangzhou could only metabolize PS and LDPE. Besides, LDPE could be degraded by mealworms from Tai'an and Shenzhen, while those from Guangzhou showed no such capability, indicating that mealworms from different regions present different metabolism effects. Furthermore, PS and LDPE are more likely to be metabolized compared with PVC.

Genome-Centered Metagenomics Analysis Reveals the Symbiotic Organisms Possessing Ability to Cross-Feed with Anammox Bacteria in Anammox Consortia.

Although using anammox communities for efficient wastewater treatment has attracted much attention, the pure anammox bacteria are difficult to obtain, and the potential roles of symbiotic bacteria in anammox performance are still elusive. Here, we combined long-term reactor operation, genome-centered metagenomics, community functional structure, and metabolic pathway reconstruction to reveal multiple potential cross-feedings during anammox reactor start-up according to the 37 recovered metagenome-assembled genomes (MAGs). We found Armatimonadetes and Proteobacteria could contribute the secondary metabolites molybdopterin cofactor and folate for anammox bacteria to benefit their activity and growth. Chloroflexi-affiliated bacteria encoded the function of biosynthesizing exopolysaccharides for anammox consortium aggregation, based on the partial nucleotide sugars produced by anammox bacteria. Chlorobi-affiliated bacteria had the ability to degrade extracellular proteins produced by anammox bacteria to amino acids to affect consortium aggregation. Additionally, the Chloroflexi-affiliated bacteria harbored genes for a nitrite loop and could have a dual role in anammox performance during reactor start-up. Cross-feeding in anammox community adds a different dimension for understanding microbial interactions and emphasizes the importance of symbiotic bacteria in the anammox process for wastewater treatment.

Ubiquity of polystyrene digestion and biodegradation within yellow mealworms, larvae of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae).

Academics researchers and "citizen scientists" from 22 countries confirmed that yellow mealworms, the larvae of Tenebrio molitor Linnaeus, can survive by eating polystyrene (PS) foam. More detailed assessments of this capability for mealworms were carried out by12 sources: five from the USA, six from China, and one from Northern Ireland. All of these mealworms digested PS foam. PS mass decreased and depolymerization was observed, with appearance of lower molecular weight residuals and functional groups indicative of oxidative transformations in extracts from the frass (insect excrement). An addition of gentamycin (30 mg g-1), a bactericidal antibiotic, inhibited depolymerization, implicating the gut microbiome in the biodegradation process. Microbial community analyses demonstrated significant taxonomic shifts for mealworms fed diets of PS plus bran and PS alone. The results indicate that mealworms from diverse locations eat and metabolize PS and support the hypothesis that this capacity is independent of the geographic origin of the mealworms, and is likely ubiquitous to members of this species.

Distribution and speciation of mercury affected by humic acid in mariculture sites at the Pearl River estuary.

At the Pearl River Estuary of southern China, mercury and its environmental problems have long been a great concern. This study investigated the distribution and speciation of mercury compounds that are significantly influenced by the increasing content of humic acid (HA, a model natural organic matter) in this region. The inorganic mercury and methyl mercury, being adsorbed and converted at different HA levels, were studied in sediments and surface water at both mariculture and their reference sites. In mariculture sediments with higher HA content (up to 4.5%), more mercury were adsorbed at different compound levels, promoting the methylation and accumulation of mercury (P < 0.05) at the sediment-water interface. Seasonal shift in environmental temperature might control the HA content, subsequently favouring mercury methylation (maximum 1.75 ±â€¯0.08 mg L-1 d-1) under warm weather conditions. In reference sites received less HA wastes, lower adsorption capacity and methylation rate were observed for mercury in sediments and surface water. Our work points to the significant roles of HA on mercury distribution and speciation both spatially and seasonally, thus addressing the impacts of mariculture activities on estuary eco-system.