Mobility, speciation of cadmium, and bacterial community composition along soil depths during microbial carbonate precipitation under simulated acid rain

An overexploitation of earth resources results in acid deposition in soil, which adversely impacts soil ecosystems and biodiversity and affects conventional heavy metal remediation using immobilization. A series of column experiments was conducted in this study to compare the cadmium (Cd) retention stability through biotic and abiotic carbonate precipitation impacted by simulated acid rain (SAR), to build a comprehensive understanding of cadmium speciation and distribution along soil depth and to elucidate the biogeochemical bacteria-soil-heavy metal interfaces. The strain of Sporosarcina pasteurii DSM 33 was used to trigger the biotic carbonate precipitation and cultivated throughout the 60-day column incubation. Results of soil pH, electrical conductivity (EC), and quantitative CdCO3/CaCO3 analysis concluded that the combination of biotic and abiotic soil treatment could reinforce soil buffering capacity as a strong defense mechanism against acid rain disturbance. Up to 1.8 ± 0.04 U/mg urease enzyme activity was observed in combination soil from day 10, confirming the sustained effect of urease-mediated microbial carbonate precipitation. Cadmium speciation and distribution analyses provided new insights into the dual stimulation of carbonate-bound and Fe/Mn-bound phases of cadmium immobilization under microbially induced carbonate precipitation (MICP). As confirmed by the microbial community analysis, outsourcing urea triggered diverse microbial metabolic responses, notably carbonate precipitation and dissimilatory iron metabolism, in both oxygen-rich topsoil and oxygen-depleted subsurface layers. The overall investigation suggests the feasibility of applying MICP for soil Cd remediation under harsh environments and stratagem by selecting microbial functionality to overcome environmental challenges.

Self-assembled silk fibroin cross-linked with genipin supplements microbial carbonate precipitation in building material

The process of microbially induced carbonate precipitation (MICP) is known to effectively improve engineering properties of building materials and so does silk fibroin (SF). Thus, in this study, an attempt was taken to see the improvement in sand, that is, basic building material coupled with MICP and SF. Urease producing Bacillus megaterium was utilized for MICP in Nutri-Calci medium. To improve the strength of SF itself in bacterial solution, it was cross-linked with genipin at the optimized concentration of 3.12 mg/mL. The Fourier transform infrared (FTIR) spectra confirmed the crosslinking of SF with genipin in bacterial solution. In order to understand how such cross-linking can improve engineering properties, sand moulds of 50 mm3 dimension were prepared that resulted in 35% and 55% more compressive strength than the one prepared with bacterial solution with SF and bacterial solution only, respectively with higher calcite content in former one. The FTIR, SEM, x-ray powder diffraction spectrometry and x-ray photoelectron spectroscopy analyses confirmed higher biomineral precipitation in bacterial solution coupled with genipin cross-linked SF. As the process of MICP is proven to replace cement partially from concrete without negatively influence mechanical properties, SF cross-linked with genipin can provide additional significance in developing low-carbon cement-based composites.

Whole cell evaluation and the enzymatic kinetic study of urease from ureolytic bacteria affected by potentially toxic elements

Microbially induced carbonate precipitation (MICP) is a biomineralization process that has various applications in environmental pollution remediation and restoration of a range of building materials. In this study, a ureolytic bacterium, Lysinibacillus sp. GY3, isolated from an E-waste site, was found as a promising catalyst for remediation of heavy metals via the MICP process. This bacterial isolate produced significant amounts of urease and showed a great persistence in immobilization of potentially toxic elements. A reference ureolytic strain, Bacillus megaterium VS1, was selected in order to compare the efficiency of Lysinibacillus sp. GY3. Study on urease localization indicated 80 % more urease activity secreted extracellularly as for Lysinibacillus sp. GY3 compared to B. megaterium VS1. From the investigation on effects of metals on both intra- and extra-cellular urease, it was clear that Lysinibacillus sp. GY3 produced the most stable urease under conditions of metal pressure, especially retaining more than 70 % activity in the presence of 1 g/L Pb²⁺ and Zn²⁺. These results suggest that this isolated microorganism could be promisingly introduced in the MICP process to stabilize complex heavy metal pollutions, with reference to the regulating ability under harsh conditions to stabilize urease activity. This species is so important both for its biological features and environmental impacts. In addition, the present study will bring new insight in the field of metal remediation coupled with enzyme engineered biotechnology.

Biochemical composite material using corncob powder as a carrier material for ureolytic bacteria in soil cadmium immobilization

Corncob powder possessing its superiority in environmental sustainability and cost, was approved with strong capability of being a replacement of biochar in facilitating the microbial carbonate precipitation process. In this study, the ureolytic bacterial strain Bacillus sp. WA isolated from a pre-acquired metal contaminated soil in Guiyu, China, was showed to be well attached on the surfaces of corncob powder, indicating the carrier's role as a durable shelter for bacterial cells. The efficient immobilization helped develop biochemical composite material (BCM) and proven to function better the calcite precipitation. Afterwards, the mechanism and multi-directional benefits of BCM in edaphic cadmium remediation were examined through pot experiment and compared with corncob powder/bacterial strain/nutrient media as control groups. Integrated lab-scale analyses emphasized the advantages of BCM by the maximum soil urease activity (up to 3.440 U/mg and increased by 214% in 28 days), maximal bacterial propagation (most abundant population in fluorescence microscopy), richest surface functional group (most remarkable OC bond and CO bond in FTIR result), notable calcite precipitation (clear calcite crystals on the surface of BCM compared to control group under SEM-EDS), and highest Cd immobilization rate (exchangeable Cd decreased by 68.54%), among all treatments. The pH and electroconductivity measurements additionally led to the mechanism of corncob powder and NBU promoting pre-existed ureolytic bacteria in soil, which demonstrated the added value of corncob to be fine carbon source and residence shelter for soil microorganism, revealing its potential in developing agricultural materials.

A critical review on microbial carbonate precipitation via denitrification process in building materials

The naturally occurring biomineralization or microbially induced calcium carbonate (MICP) precipitation is gaining huge attention due to its widespread application in various fields of engineering. Microbial denitrification is one of the feasible metabolic pathways, in which the denitrifying microbes lead to precipitation of carbonate biomineral by their basic enzymatic and metabolic activities. This review article explains all the metabolic pathways and their mechanism involved in the MICP process in detail along with the benefits of using denitrification over other pathways during MICP implementation. The potential application of denitrification in building materials pertaining to soil reinforcement, bioconcrete, restoration of heritage structures and mitigating the soil pollution has been reviewed by addressing the finding and limitation of MICP treatment. This manuscript further sheds light on the challenges faced during upscaling, real field implementation and the need for future research in this path. The review concludes that although MICP via denitrification is an promising technique to employ it in building materials, a vast interdisciplinary research is still needed for the successful commercialization of this technique.

Sustainable bio-bricks prepared with synthetic urine enabled by biomineralization reactions

In this study, mineralization during brick preparation was performed with ureolytic bacterium, Lysinibacillus fusiformis that use urine as a substrate, omitting the heat that is normally required. Artificial urine for reasons of standardization was used to grow the bacterium for bio-bricks made of clay and cement, but their mineralization was enabled by biological activity instead of by heat. Scanning electron microscopy and energy dispersion X-ray spectroscopy were conducted to analyse the microstructures formed by L. fusiformis that precipitated various minerals in synthetic urine. The brick specimens were tested for compressive strength that was 59% more than control ones, whereas porosity of bio-bricks was 13% compared to 22% of control specimens. The minerals formed in the bio-bricks confirmed as struvite, apatite and calcite by Fourier-transform infrared spectroscopy and X-ray diffraction spectra, were responsible for improved strength and reduced porosity. The research provided evidence in utilizing ureolytic bacteria as a mode to mineralize clay in brick production with the use of (artificial) urine as a substrate.

Ureolytic bacteria from electronic waste area, their biological robustness against potentially toxic elements and underlying mechanisms

Ureolytic bacteria can be a promising mediator used for the immobilization of potentially toxic elements via microbially-induced carbonate precipitation (MICP) process from biodegradable ions to carbonate form. Electronic waste (E-waste) environment is very complex compared to general metal contaminated soil, however, MICP has not been studied under such an environment. In this study, three bacterial strains were successfully isolated from an E-waste area in Guiyu, China, and indicated to have positive ureolytic behavior with significant heavy metal resistance (specific to Cu and Pb), among which, a strain of Lysinibacillus sp. was proven to show a great persistence in heavy metal immobilization. This featured strain can tolerate up to 100 ppm copper and 1000 ppm lead according to minimal inhibitory concentration (MIC) results, and its urease activity was well-adapted to metal effects. Results also revealed the positive correlation (R² = 0.9819) between metal concentrations and surface layer protein content present in bacterial cells. The underlying mechanism on the role of S-layer protein in heavy metal immobilization during biocalcification was elucidated. The metabolic system of heavy metal resistance for these E-waste derived isolates is novel and represents a point of interest for possible environmental applications to immobilize toxic heavy metals from electronic waste sites.

Impact of the COVID-19 pandemic on air pollution in Chinese megacities from the perspective of traffic volume and meteorological factors

During 2020, the COVID-19 pandemic resulted in a widespread lockdown in many cities in China. In this study, we assessed the impact of changes in human activities on air quality during the COVID-19 pandemic by determining the relationships between air quality, traffic volume, and meteorological conditions. The megacities of Wuhan, Beijing, Shanghai, and Guangzhou were selected as the study area, and the variation trends of air pollutants for the period January-May between 2016 and 2020 were analyzed. The passenger volume of public transportation (PVPT) and the passenger volume of taxis (PVT) along with data on precipitation, temperature, relative humidity, wind speed, and boundary layer height were used to identify and quantify the driving force of the air pollution variation. The results showed that the change rates of fine particulate matter (PM_2.5), NO₂, and SO₂ before and during the lockdown in the four megacities ranged from -49.9% to 78.2% (average: -9.4% ± 59.3%), -55.4% to -32.3% (average: -43.0% ± 9.7%), and - 21.1% to 11.9% (average: -10.9% ± 15.4%), respectively. The response of NO₂ to the lockdown was the most sensitive, while the response of PM_2.5 was smaller and more delayed. During the lockdown period, haze from uninterrupted industrial emissions and fireworks under the effect of air mass transport from surrounding areas and adverse climate conditions was probably the cause of abnormally high PM_2.5 concentrations in Beijing. In addition, the PVT was the most significant factor for NO₂, and meteorology had a greater impact on PM_2.5 than NO₂ and SO₂. There is a need for more national-level policies for limiting firework displays and traffic emissions, as well as further studies on the formation and transmission of secondary air pollutants.

Environmental and health impacts due to e-waste disposal in China - A review

E-waste is discarded and shipped mostly to developing countries located in Asian continent for disposal from other developed countries. Especially 70% of the world's e-waste ends up in Guiyu, a small town located in Guangdong Province of China. As little as 25% is recycled in formal recycling centers with adequate protection for workers and the other e-waste arrived in those areas is not handled in organized manner. As per reports only roughly 12.5% of e-waste is actually recycled, and the recycling efforts in those regions are primitive and result in toxic substances being leached into the surrounding ecosystems. In addition to persistent organic pollutants, there are many heavy metals found in the ground and river sediments in Guiyu, exceeding the threshold set to protect human health. Those areas are no longer suitable for growing food, and water is unsafe for drinking, due to the amount of toxins leached into the groundwater and land. Hazardous threats to environment and human health due to hazardous substances of e-waste all around China, as well as the current e-waste management were documented in this review. The article concludes with controlled contamination sources, and eco-friendly and efficient remediation technologies to solve e-waste problem in China.

Effect of simulated acid rain on the stability of calcium carbonate immobilized by microbial carbonate precipitation

The stability of carbonate products resulting from microbially induced carbonate precipitation (MICP) under acid rain is under question. The present study investigated the stability of CaCO₃ precipitated by MICP in soil under simulated acid rain (SAR). Soils were treated continuously for two months with four SAR pH levels: 3.5, 4.5, 5.5, and 7.0. During SAR, biostimulation using nutrient broth containing urea and calcium chloride was adopted to ensure CaCO₃ precipitation. At the end of treatments, soil samples from top and bottom layers were analyzed for bacterial diversity by Illumina MiSeq sequencing, Fourier transform infrared (FTIR) spectroscopy for identification of chemical functional groups related to calcite precipitation, and X-ray diffraction (XRD) for identification of the main crystalline phases. The analysis identified several ureolytic bacteria mainly from Arthrobacter and Sporosarcina genera in SAR-treated soils accelerated with biostimulation, and urease quantities of greater than 300 mg NH₄⁺ per kg soil at all pH levels. The precipitation of CaCO₃ was pronounced and its stability was maintained even when the pH was as low as 3.5. The results obtained in this study are helpful to the scientific community to ensure the immobilization of heavy metals with microbial carbonate precipitation in soil under acid rain.

The characteristics and local-regional contributions of atmospheric black carbon over urban and suburban locations in Shanghai, China

Black carbon (BC), produced from the incomplete combustion of carbonaceous fuels, has emerged as a major contributor to global climate change with adverse health effects. Based on one-year (2016.06.01-2017.06.30) equivalent black carbon (eBC) measurements, this study analyzed the characteristics of eBC concentrations and the local-regional contributions at an urban site (Pudong, PD) and a suburban site (Qingpu, QP) in Shanghai, China. The results showed that the annual average eBC concentrations were 1.17 ± 0.61 μg m^-3 and 2.09 ± 0.97 μg m^-3 at PD and QP, respectively. The high eBC concentrations occurred in winter and at weekends both for PD and QP. There were significant negative correlation coefficients between the daily eBC, the daily wind speed (WS) and the daily boundary layer height (BLH) at PD (r_ws: 0.45, r_blh = -0.35, p < 0.01) and QP (r_ws: 0.49, r_blh = -0.32, p < 0.01). And the relative higher eBC concentrations coincided with southerly, southwesterly and westerly winds although these winds had lower frequencies. This could be related to the agricultural fire in these directions during summer harvesttime. The significant partial correlation coefficients of eBC-CO (r_u:0.37-0.64, r_s:0.18-0.44, p < 0.01) and eBC-NO₂ (r_u:0.49-0.74, r_s:0.38-0.75, p < 0.01) could suggest that eBC mainly come from vehicular exhaust emissions in Shanghai. Besides, the higher eBC/PM_2.5 (5.29% ± 1.94%) and eBC/CO(0.30% ± 0.14%) at QP indicated the more combustion activities and diesel-powered vehicle emissions in suburban areas. The concentration weighted trajectory (CWT) analysis indicated that the surrounding areas at the junction of Shanghai, Jiangsu, and Zhejiang provinces seemed to be relatively the most important sources outside of Shanghai.

Biostimulation of calcite precipitation process by bacterial community in improving cement stabilized rammed earth as sustainable material

Rammed earth has been enjoying a renaissance as sustainable construction material with cement stabilized rammed earth (CSRE). At the same time, it is important to convert CSRE to be a stronger, durable, and environment-friendly building material. Bacterial application is established to improve cementitious materials; however, bioaugmentation is not widely acceptable by engineering communities. Hence, the present study is an attempt applying biostimulation approach to develop CSRE as sustainable construction material. Results showed that biostimulation improved the compressive strength of CSRE by 29.6% and resulted in 27.7% lower water absorption compared to control. The process leading to biocementation in improving CSRE was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope-energy dispersive spectrometer. Further, Illumina MiSeq sequencing was used to investigate changes in bacterial community structures after biostimulation that identified majority of ureolytic bacteria dominated by phylum Firmicutes and genus Sporosarcina playing role in biocementation. The results open a way applying biological principle that will be acceptable to a wide range of civil engineers.

Biostimulation of carbonate precipitation process in soil for copper immobilization

The urease-based microbially induced carbonate precipitation (MICP) is known as effective remediation strategy in soil metals remediation; however, all related studies confined to bioaugmentation. In the present study, biostimulation process was adopted for the first time in accelerating MICP in copper (Cu) immobilization in soil. The abundance, composition, and diversity of the bacterial community after biostimulation were assessed with MiSeq Illumina sequencing analysis that confirmed number and types of ureolytic and calcifying bacteria grown significantly leading to MICP process, compared to untreated soil. The results demonstrated that biostimulation induced calcite precipitation in soil that immobilized Cu mainly in carbonated fraction of soil, while soluble-exchangeable fraction decreased from 45.54 mg kg^-1 to 1.55 mg kg^-1 Cu in soil. Scanning electron microscopy (SEM) cum energy-dispersive X-ray spectroscopy (EDX) evaluated structure and elemental composition in Cu immobilization after biostimulation. Fourier Transform-Infra Red (FTIR) spectroscopy depicted functional chemical groups involved in copper immobilization, while X-Ray Diffraction (XRD) identified main crystalline phases or biominerals formed during biostimulation in order to carryout Cu remediation from soil.

Fly ash incorporated with biocement to improve strength of expansive soil

Microbially induced calcium carbonate precipitation (MICP) results in the formation of biocement (BC). This process, also known as biocementation, is recently widely used to improve the strength and durability of building materials including soils. In the present study, effectiveness of biocement as admixture with fly ash (FA) was investigated as first few studies to improve geotechnical properties of expansive soils. Biocement precipitated by Bacillus megaterium was blend with four formulations of fly ash at concentrations of 0, 10, 25 and 50%, namely 0% FABC, 10% FABC, 25% FABC, and 50% FABC, respectively. These formulations were separately added to expansive soils. Specimens with 25% FABC resulted in significant improvement in unconfined compressive strength of expansive soil that was more than two-times higher than control. Further, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses characterized microstructures of soil specimens, and depicted the process of MICP in improving strength of expansive soils. This research indicates that incorporation of biocement in fly ash is an effective means of increasing the strength of expansive soils.

Biomineralization in metakaolin modified cement mortar to improve its strength with lowered cement content

The role of industrial byproduct as supplementary cementitious material to partially replace cement has greatly contributed to sustainable environment. Metakaolin (MK), one of such byproduct, is widely used to partial replacement of cement; however, during cement replacement at high percentage, it may not be a good choice to improve the strength of concrete. Thus, in the present study, biocement, a product of microbially induced carbonate precipitation is utilized in MK-modified cement mortars to improve its compressive strength. Despite of cement replacement with MK as high as 50%, the presented technology improved compressive strength of mortars by 27%, which was still comparable to those mortars with 100% cement. The results proved that biomineralization could be effectively used in reducing cement content without compromising compressive strength of mortars. Biocementation also reduced the porosity of mortars at all ages. The process was characterized by SEM-EDS to observe bacterially-induced carbonate crystals and FTIR spectroscopy to predict responsible bonding in the formation of calcium carbonate. Further, XRD analysis identified bio/minerals formed in the MK-modified mortars. The study also encourages combining biological role in construction engineering to solve hazardous nature of cement and at same time solve the disposal problem of industrial waste for sustainable environment.

The large-scale process of microbial carbonate precipitation for nickel remediation from an industrial soil

Microbial carbonate precipitation is known as an efficient process for the remediation of heavy metals from contaminated soils. In the present study, a urease positive bacterial isolate, identified as Bacillus cereus NS4 through 16S rDNA sequencing, was utilized on a large scale to remove nickel from industrial soil contaminated by the battery industry. The soil was highly contaminated with an initial total nickel concentration of approximately 900 mg kg^-1. The soluble-exchangeable fraction was reduced to 38 mg kg^-1 after treatment. The primary objective of metal stabilization was achieved by reducing the bioavailability through immobilizing the nickel in the urease-driven carbonate precipitation. The nickel removal in the soils contributed to the transformation of nickel from mobile species into stable biominerals identified as calcite, vaterite, aragonite and nickelous carbonate when analyzed under XRD. It was proven that during precipitation of calcite, Ni²⁺ with an ion radius close to Ca²⁺ was incorporated into the CaCO₃ crystal. The biominerals were also characterized by using SEM-EDS to observe the crystal shape and Raman-FTIR spectroscopy to predict responsible bonding during bioremediation with respect to Ni immobilization. The electronic structure and chemical-state information of the detected elements during MICP bioremediation process was studied by XPS. This is the first study in which microbial carbonate precipitation was used for the large-scale remediation of metal-contaminated industrial soil.

Microbially-induced Carbonate Precipitation for Immobilization of Toxic Metals

Rapid urbanization and industrialization resulting from growing populations contribute to environmental pollution by toxic metals and radionuclides which pose a threat to the environment and to human health. To combat this threat, it is important to develop remediation technologies based on natural processes that are sustainable. In recent years, a biomineralization process involving ureolytic microorganisms that leads to calcium carbonate precipitation has been found to be effective in immobilizing toxic metal pollutants. The advantage of using ureolytic organisms for bioremediating metal pollution in soil is their ability to immobilize toxic metals efficiently by precipitation or coprecipitation, independent of metal valence state and toxicity and the redox potential. This review summarizes current understanding of the ability of ureolytic microorganisms for carbonate biomineralization and applications of this process for toxic metal bioremediation. Microbial metal carbonate precipitation may also be relevant to detoxification of contaminated process streams and effluents as well as the production of novel carbonate biominerals and biorecovery of metals and radionuclides that form insoluble carbonates.

Optimization of Bioethanol Production Using Whole Plant of Water Hyacinth as Substrate in Simultaneous Saccharification and Fermentation Process

Water hyacinth was used as substrate for bioethanol production in the present study. Combination of acid pretreatment and enzymatic hydrolysis was the most effective process for sugar production that resulted in the production of 402.93 mg reducing sugar at optimal condition. A regression model was built to optimize the fermentation factors according to response surface method in saccharification and fermentation (SSF) process. The optimized condition for ethanol production by SSF process was fermented at 38.87°C in 81.87 h when inoculated with 6.11 ml yeast, where 1.291 g/L bioethanol was produced. Meanwhile, 1.289 g/L ethanol was produced during experimentation, which showed reliability of presented regression model in this research. The optimization method discussed in the present study leading to relatively high bioethanol production could provide a promising way for Alien Invasive Species with high cellulose content.

Bio-grout based on microbially induced sand solidification by means of asparaginase activity

Bio-grout, a new ground improvement method, has been recently developed to improve the mechanical properties, decrease the permeability of porous materials, reinforce or repair cementitious materials and modify the properties of soil or sand. Bio-grout production depends on microbially induced calcite precipitation (MICP), which is driven mainly by an enzyme, urease. However, urease-based MICP process produces excessive ammonia, in addition to secondary pollution generated by urea that is used as substrate in it. In the present study, we reported asparaginase-based MICP process for sand bio-grout development using Bacillus megaterium, and results were also compared with urease-based bio-grouts. The asparaginase activity led to significantly less ammonia production compared to urease without compromising with desired properties of a novel grout. The UCS of bio-grout was obtained at 980 kPa, while the permeability was decreased substantially. The mineralogical composition of precipitated substance was identified as calcite using XRD and the crystal morphology was observed under SEM. The mass percentage of calcite in bio-grout was calculated by thermogravimetric analysis and XCT verified calcite precipitation in it. The results confirmed that biocalcification by means of bacterial asparaginase is a potential solution for geotechnical problems. The asparaginase-based MICP process could be of wider acceptance in future.

A comparison of the potential health risk of aluminum and heavy metals in tea leaves and tea infusion of commercially available green tea in Jiangxi, China

Heavy metals and Al in tea products are of increasing concern. In this study, contents of Al, Cd, Co, Cr, Cu, Ni, and Pb in commercially available green tea and its infusions were measured by ICP-MS and ICP-AES. Both target hazard quotient (THQ) and hazard index (HI) were employed to assess the potential health risk of studied metals in tea leaves and infusions to drinkers. Results showed that the average contents of Al, Cd, Co, Cr, Cu, Ni, and Pb in tea leaves were 487.57, 0.055, 0.29, 1.63, 17.04, 7.71, and 0.92 mg/kg, respectively. Except for Cu, metal contents were within their maximum limits (1, 5, 30, and 5 mg/kg for Cd, Cr, Cu, and Pb, respectively) of current standards for tea products. Concentrations of metals in tea infusions were all below their maximum limits (0.2, 0.005, 0.05, 1.0, 0.02, and 0.01 mg/L for Al, Cd, Cr(VI), Cu, Ni, and Pb, respectively) for drinking water, and decreased with the increase of infusion times. Pb, Cd, Cu, and Al mainly remained in tea leaves. The THQ from 2.33 × 10(-5) to 1.47 × 10(-1) and HI from1.41 × 10(-2) to 3.45 × 10(-1) values in tea infusions were all less than 1, suggesting that consumption of tea infusions would not cause significant health risks for consumers. More attention should be paid to monitor Co content in green tea. Both THQ and HI values decreased with the increase of infusion times. Results of this study suggest that tea drinkers should discard the first tea infusion and drink the following infusions.

Influence of calcium sources on microbially induced calcium carbonate precipitation by Bacillus sp. CR2

Stimulation of microbially induced calcium carbonate precipitation (MICCP) is likely to be influenced by calcium sources. In order to study such influences, we performed MICCP using Bacillus sp. CR2 in nutrient broth containing urea, supplemented with different calcium sources (calcium chloride, calcium oxide, calcium acetate and calcium nitrate). The experiment lasted 7 days, during which bacterial growth, urease activity, calcite production and pH were measured. Our results showed that calcium chloride is the better calcium source for MICCP process, since it provides higher urease activity and more calcite production. The influences of calcium sources on MICCP were further studied using Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. These analyses confirmed that the precipitate formed was CaCO3 and composed of predominantly calcite crystals with a little amount of aragonite and vaterite crystals. The maximum yield of calcite precipitation was achievable with calcium chloride followed by calcium nitrate as a calcium source. The results of present study may be applicable to media preparation during efficient MICCP process.

Potential for nutrient removal by integrated remediation methods in a eutrophicated artificial lake - a case study in Dishui Lake, Lingang New City, China

A new integrated water remediation technology, including a floating bed, a buffer zone of floating plants, enclosed 'water hyacinth' purification, economic aquatic plants and near-shore aquatic plant purification, was used in Dishui Lake to improve its water quality. A channel of 1,000 m length and 30 m width was selected to implement pilot-scale experiments both in the static period and the continuous water diversion period. The results showed that the new integrated water remediation technology exhibited the highest removal rate for permanganate index in a static period, which achieved 40.6%. The average removal rates of total nitrogen (TN), ammonia nitrogen (NH3-N) and total phosphorus (TP) in a static period were 23.2, 21.6 and 19.1%, respectively. However, it did not exhibit an excellent removal rate for pollutants in the continuous water diversion period. The average removal rates for all pollutants were below 10%. In winter, the new integrated remediation technology showed efficient effects compared to others. The average removal rate for CODMn, TN, NH3-N and TP were 7, 5.3, 7.6 and 6.5%, respectively. Based on our results, the new integrated water remediation technology was highly efficient as a purification system, especially during the static period in winter.

Remediation of Cr(VI) from chromium slag by biocementation

Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM-EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.

Bioremediation of strontium (Sr) contaminated aquifer quartz sand based on carbonate precipitation induced by Sr resistant Halomonas sp

Contamination of aquifers or sediments by radioactive strontium ((90)Sr) is a significant environmental problem. In the present study, microbially induced calcite precipitation (MICP) was evaluated for its potential to remediate strontium from aquifer quartz sand. A Sr resistant urease producing Halomonas sp. was characterized for its potential role in bioremediation. The bacterial strain removed 80% of Sr from soluble-exchangeable fraction of aquifer quartz sand. X-ray diffraction detected calcite, vaterite and aragonite along with calcite-strontianite (SrCO(3)) solid solution in bioremediated sample with indications that Sr was incorporated into the calcite. Scanning electron micrography coupled with energy-dispersive X-ray further confirmed MICP process in remediation. The study showed that MICP sequesters soluble strontium as biominerals and could play an important role in strontium bioremediation from both ecological and greener point of view.

Proteomic analysis of Mn-induced resistance to powdery mildew in grapevine

Previous studies documented that metal hyperaccumulation armours plants with direct defences against pathogens. In the present study, it was found that high leaf Mn concentrations (<2500 µg g(-1)) induced grapevine resistance to powdery mildew [Uncinula necator (Schw.) Burr]. Manganese delayed pathogen spreading after powdery mildew (PM) inoculation, but did not directly inhibit pathogen growth on a long-term basis. It was postulated that the grapevine resistance resulted from the induction of protective mechanisms in planta. To test this hypothesis, the proteome profile was analysed by Difference Gel Electrophoresis (DIGE) methods to identify proteins that are putatively involved in pathogen resistance. A high Mn concentration caused little oxidative pressure in grapevine, but oxidative stress was deeply enhanced by PM stress. Except for a few proteins that were related to oxidative pressure and proteins specially regulated by Mn or PM, most of the detected proteins exhibited similar changes under excess Mn stress and under PM stress, suggesting that similar signalling processes mediate the responses to the two stresses. As well as PM stress, high leaf Mn concentration significantly enhanced salicylic acid concentration and increased the expression of proteins involved in ethylene and jasmonic acid synthesis. The proteins related to pathogen resistance were also enhanced by excess Mn, including a PR-like protein, an NBS-LRR analogue, and a JOSL protein, and this was accompanied by the increased activity of phenylalanine ammonia lyase. It was concluded that high leaf Mn concentration triggered protective mechanisms against pathogens in grapevine.

Bioremediation of Pb-contaminated soil based on microbially induced calcite precipitation

To remediate lead (Pb)-contaminated soils, it is proposed that microbially induced calcite precipitation (MICP) would provide the best alternative to other remediation technologies. In this study, Pb bioremediation in soils was investigated using the calcite-precipitating bacterium Kocuria flava. Results indicate that the Pb is primarily associated with the carbonate fraction in bioremediated soil samples. The bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated. This research provides insight into the geochemistry occurring in the MICP-based Pb-remediated soils, which will help in remediation decisions.

Biomineralization based remediation of As(III) contaminated soil by Sporosarcina ginsengisoli

Arsenic is a highly toxic metalloid and has posed high risk to the environment. As(III) is highly mobile in soil and leached easily into groundwater. The current remediation techniques are not sufficient to immobilize this toxic element. In the present study, an As(III) tolerant bacterium Sporosarcina ginsengisoli CR5 was isolated from As contaminated soil of Urumqi, China. We investigated the role of microbial calcite precipitated by this bacterium to remediate soil contaminated with As(III). The bacterium was able to grow at high As(III) concentration of 50mM. In order to obtain arsenic distribution pattern, five stage soil sequential extraction was carried out. Arsenic mobility was found to significantly decrease in the exchangeable fraction of soil and subsequently the arsenic concentration was markedly increased in carbonated fraction after bioremediation. Microbially induced calcite precipitation (MICP) process in bioremediation was further confirmed by ATR-FTIR and XRD analyses. XRD spectra showed presence of various biomineralization products such as calcite, gwihabaite, aragonite and vaterite in bioremediated soil samples. The results from this study have implications that MICP based bioremediation by S. ginsengisoli is a viable, environmental friendly technology for remediation of the arsenic contaminated sites.

Plant high tolerance to excess manganese related with root growth, manganese distribution and antioxidative enzyme activity in three grape cultivars

The cuttings of grape (Vitis vinifera Linn.) were exposed to Hoagland's solution containing five different manganese (Mn) concentrations to investigate Mn toxicity and the possible detoxifying responses. Three genotypes (i.e. cultivars Combiner, Jingshou and Shuijing) were used in present study. The results showed that grape species is highly tolerant to excess Mn. The plant growth is stimulated by as high as 15 or 30 mM Mn, and then depressed by higher Mn levels. The grape tolerance to excess Mn is related with plant capacity to keep constant or increased root growth as well as to keep high root activity. Also, the grape could employ some effective but intraspecific strategies to detoxify cellular Mn stress by excluding excess Mn out of leaf tissues or by enhancing antioxidative capacity. On the other hand, the present study showed that there existed different (or contrast) distribution pattern for excess Mn in grape. Majority of Mn was transferred and accumulated in the above-ground part in Combiner while Jingshou stored most Mn in root systems. For the first time our result showed the extreme tolerance and contrast performance at Mn translocation in an important fruit species with revealed genomic information.

Evaluation of a BWTK for detection of total coliforms, E. coli and emerging pathogens from drinking water: comparison with standard MPN method

A defined substrate method media in bacteriological water testing kit (BWTK) has been developed to recover and detect the presence/absence of total coliforms and emerging pathogens from drinking water without the need for the confirmatory or complete tests. This method is based on technology that uses a hydrolysable substrate as a specific indicator- nutrient for the target microbes. To perform the test, one only has to add water to the ingredients in the BWTK and incubate at room temperature for a time period of 48 hrs. The target microbes remain viable in the positive kit for at least 10 days and further bacterial isolates from BWTK were characterized phenotypically, molecular identified by sequencing of 16SrRNA gene and antibiotic sensitivity was determined. All of the emerging bacterial isolates were haemolytic and multiple resistant to antibiotics. The epidemiological surveillance of drinking water revealed the occurrence of emerging pathogens responsible for causing acute gastrointestinal illness, soft tissue infections, meningitis, enteritis to acute mesenteric lymphadenitis as Yersinia enterocolitica (94%) and Aeromonas hydrophila (79%). The conventional methods (IS-10500-1991 BIS New Delhi, India) cannot predict the presence of these potentially enteropathogenic microorganisms in drinking water. There are currently no suitable microbiological criteria for the detection of emerging pathogens. In response to these limitations a BWTK has been developed for regularly monitoring of drinking water quality for appraisal to public health officials and take corrective measures regarding health risk when desired.