Construction of algal-bacterial consortia using green microalgae Chlorella vulgaris and As(III)-oxidizing bacteria: As tolerance and metabolomic profiling

Bioremediation became a promising technology to resolve arsenic (As) contamination in aquatic environment. Since monoculture such as microalgae or bacteria was sensitive to environmental disturbance and vulnerable to contamination, green microalgae Chlorella vulgaris and arsenite (As(III)) - oxidizing bacteria Pseudomonas sp. SMS11 were co-cultured to construct algal-bacterial consortia in the current study. The effects of algae-bacteria (A:B) ratio and exposure As(III) concentration on algal growth, As speciation and metabolomic profile were investigated. Algal growth arrested when treated with 100 mg/L As(III) without the co-cultured bacteria. By contrast, co-cultured with strain SMS11 significantly enhanced As tolerance in C. vulgaris especially with A:B ratio of 1:10. All the As(III) in culture media of the consortia were oxidized into As(V) on day 7. Methylation of As was observed on day 14. Over 1% and 0.5% of total As were converted into dimethylarsinic acid (DMA) after 21 days cultivation when the initial concentrations of As(III) were 1 and 10 mg/L, respectively. Metabolomic analysis was further performed to reveal the response of consortia metabolites to external As(III). The enriched metabolomic pathways were associated with carbohydrate, amino acid and energy metabolisms. Tricarboxylic acid cycle and glyoxylate and dicarboxylate metabolism were upregulated under As stress due to their biological functions on alleviating oxidative stress and protecting cells. Both carbohydrate and amino acid metabolisms provided precursors and potential substrates for energy production and cell protection under abiotic stress. Alterations of the pathways relevant to carbohydrate or amino acid metabolism were triggered by energy requirement.

As(III)-Oxidizing Bacteria Alleviate Arsenite Toxicity via Reducing As Accumulation, Elevating Antioxidative Activities and Modulating Ionome in Rice (Oryza sativa L.)

Paddy rice trends to accumulate more arsenic (As) from soils than other terrestrial crops. The toxicity and mobility of As mainly depend on its chemical species. Transformation of arsenite [As(III)] into arsenate [As(V)] would be a promising method to mitigate As toxicity. In the current study, As(III)-oxidizing strain SMS11 isolated from As-contaminated soils was employed for As remediation. Co-cultured with SMS11 alleviated As(III) stress to the rice plants by increasing the length and biomass of rice shoots up to 10% and 15%, respectively. Evaluation of oxidative stress indices showed that the activity of catalase in the rice shoots was weakened when exposed to As(III), increasing the risk of hydroxyl radical (·OH) formation. When co-cultivated with the bacteria, ·OH formation was significantly inhibited in the rice shoots. The ionomes of the rice plants were impacted by the external conditions. As(III) stress significantly disturbed ionome homeostasis in the rice plants. Uptake of As simultaneously elevated the levels of macro and nutrient elements such as Mg, P, K, Ca, and Zn in the rice shoots. The ionomic variation in the rice plants under As(III) stress was mitigated by inoculated with SMS11. The results represented that the As(III)-oxidizing bacteria alleviated external As(III) stress to the rice plants through elevating antioxidative activities and modulating ionome homeostasis.

Spatial and seasonal variation of arsenic speciation in Pantanal soda lakes

The occurrence of high arsenic concentrations (up to 3000 μg L^-1) in water of soda lakes of the Pantanal wetland is a remarkable case of natural arsenic contamination in South America. However, little is known about arsenic speciation in this environment, particularly regarding speciation changes related to lake trophic status and seasonal variations. To fill this gap, arsenic speciation analysis was carried out in surface (SW) and subsurface (SSW) waters sampled in five soda lakes with different eutrophication status, in two dry and one wet season. As(V) was the dominant species in these waters, while As(III), DMA, MMA and likely complex organic species were present in lower amounts. The results allow to conclude that the arsenic speciation in SW and SSW varies seasonally according to the regional wet or dry periods and lake water levels. In eutrophic turbid and in oligotrophic vegetated soda lakes, arsenic speciation was also characterized by spatial differences between edge and center or between the SW and SSW. Cyanobacteria or macrophytes/algae are involved in arsenic biotransformation in soda lakes through its metabolic and detoxification processes. Significant variation in surface water arsenic speciation occurs as a result of seasonal primary production fluctuation or water arsenic concentration changes in the soda lakes, increasing organoarsenics in dry periods, whereas in flood periods, As(V) prevails. Spatial distribution of arsenic species is significantly impacted by biogeochemical conditions at the water/sediment interface in soda lakes.

Arsenic contamination in rice, radiation and chemical methods of measurement, and implications for food safety

Rice products, including those given to infants, could be naturally polluted with arsenic. This issue for all age groups should be a top priority for the world food industry and the public. Food regulators assume incorrectly that infants' food and other rice products are safe, and health, agriculture and commerce authorities follow no clear guidelines. A common measure has been to place a ML on the amount of iAs in white rice and food intended for children and pregnant women. Although oAs is less toxic than iAs, it is still toxic; consequently, the ML of arsenic for the different age groups should be also specified. However, the ML of iAs in polished white rice for infants is very low (100 μg/kg for infants and 200 μg/kg for adults) and is difficult to measure. Using neutron activation for research is very useful in improving safety standards in the food industry. The second purpose of this review study is to report on the experimental results and methods used for measurements adopted at the Delft Reactor in the Netherlands with a colleague of the quantity of arsenic in 21 samples of different rice products from a variety of brands.

Detoxification and removal of arsenite by Pseudomonas sp. SMS11: Oxidation, biosorption and bioaccumulation

Arsenite [As(III)] oxidizing bacteria have been widely studied for their detoxification ability through transforming As(III) into arsenate [As(V)]. However, few was focused on removal capacity of arsenic (As). In the current study, As(III) oxidation accompanied with removal of total As was observed in Pseudomonas sp. SMS11. The biosorption (unbinding and surface binding) and bioaccumulation (intracellular uptake) of As by the cells were investigated. Biosorption isotherm was defined adequately by Langmuir and Freundlich models. Biosorption kinetics was recommended by pseudo second-order model. For comparison, the bacteria were inoculated in pure water or culture media amended with different concentrations of As(III) to evaluate the remediation capacity without or with bacterial growth. After removing unbound As, surface bound and intracellular As were sequentially separated using EDTA elution and acidic extraction from bacterial cells. Without bacterial growth, oxidation of As(III) was retarded and the maximum values of surface bound and intracellular As were 4.8 and 10.5 mg/g, respectively. Efficient oxidation and high adsorption capacity were observed after bacterial growth. The surface bound and intracellular As achieved up to 555.0 and 2421.5 mg/g, respectively. Strain SMS11 exhibited great accumulation capacity of As in aqueous solutions, indicating potential application in detoxification and removal of As(III) contamination. The results also suggested that bioremediation via bacteria should be based on living cells and bacterial growth rate.

Ionome profiling and arsenic speciation provide evidence of arsenite detoxification in rice by phosphate and arsenite-oxidizing bacteria

Arsenite (As(III)) as the most toxic and mobile form is the dominant arsenic (As) species in flooded paddy fields, resulting in higher accumulation of As in paddy rice than other terrestrial crops. Mitigation of As toxicity to rice plant is an important way to safeguard food production and safety. In the current study, As(III)-oxidizing bacteria Pseudomonas sp. strain SMS11 was inoculated with rice plants to accelerate conversion of As(III) into lower toxic arsenate (As(V)). Meanwhile, additional phosphate was supplemented to restrict As(V) uptake by the rice plants. Growth of rice plant was significantly inhibited under As(III) stress. The inhibition was alleviated by the introduction of additional P and SMS11. Arsenic speciation showed that additional P restricted As accumulation in the rice roots via competing common uptake pathways, while inoculation with SMS11 limited As translocation from root to shoot. Ionomic profiling revealed specific characteristics of the rice tissue samples from different treatment groups. Compared to the roots, ionomes of the rice shoots were more sensitive to environmental perturbations. Both extraneous P and As(III)-oxidizing bacteria SMS11 could alleviate As(III) stress to the rice plants through promoting growth and regulating ionome homeostasis.

Understanding the slight inhibition of high As(III) stress on nitritation process: Insights from arsenic speciation and microbial community analyses

Nitritation process with ammonia-oxidizing bacteria frequently suffers inhibition from heavy metals in industrial wastewater treatment. However, As(III), one of the most toxic metalloids, showed slight inhibition though the arsenic accumulation content in the sludge reached 91.8 mg L^-1 in this study. Here, we combined long-term reactor operation with microbiological analyses to explore the slight inhibition mechanisms of As(III) on nitritation consortia. The results showed that no obvious changes induced by As(III) occurred in apparent characteristics and morphology of the nitritation consortia, whereas dosing As(III) induced shifts in the arsenic speciation and microbial community. 84.1% of As(III) was oxidized to As(V) in the acclimated sludge, decreasing the toxicity of As(III) to nitritation consortia. Insight to the microbial community, the relative abundances of Thermaceae and Phycisphaeraceae responsible for As(III) oxidation were increased to 7.4% and 6.6% under the stress of high-concentration As(III), respectively. Further, these increased arsenite-oxidizing bacteria probably accepted electron acceptor NO₂^- from ammonia-oxidizing bacteria to oxidize As(III). Our results indicated that microbial As(III) oxidation was the dominant detoxification pathway, providing new insights into nitritation characteristics under long-term As(III) stress.

Arsenic Species Analysis at Trace Level by High Performance Liquid Chromatography with Inductively Coupled Plasma Mass Spectrometry

A sensitive and accurate simultaneous continuous analysis for six arsenic species including arsenobetaine (AsB), arsenocholine (AsC), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenite (As^III), and arsenate (As^V) has been developed by high performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). An anion-exchange column of Hamilton PRP-X100 (Switzerland) was applied for separation of the six arsenic species with gradient elution of 1.25 mmol/L Na₂HPO₄ and 11.0 mmol/L KH₂PO₄ as the mobile phase A and 2.5 mmol/L Na₂HPO₄ and 22.0 mmol/L KH₂PO₄ as the mobile phase B. The linearity ranges for AsB, AsC, MMA, DMA, As^III, and As^V were between 0.5 and 50.0 μg/L, and the detection limits of the six arsenic species were all within 0.01–0.35 ng/L. The relative standard deviations (RSDs) were within 2.26–3.68% and the recovery rates of samples ranged from 95 to 103%. The proposed method was applied for the arsenic speciation analysis of sediment pore-water samples, which were taken from the supernatant after centrifugation and filtration.

Ionomic profile and arsenic speciation in Semisulcospira cancellata, a freshwater shellfish from a mine-impacted river in China

Freshwater aquatic environment close to cities and industrial areas is more sensitive than marine environment. The freshwater shellfish Semisulcospira cancellate was introduced as a bioindicator to monitor the heavy metal contamination in the river through ionomic profiles and arsenic speciation. The shellfish samples were collected near four cities along the Xiang River in China. The concentrations of elements including Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Cd, Sn, Sb, Ba, and Pb were determined using ICP-MS. Multivariate statistical analyses such as Pearson's correlation analysis and principle component analysis (PCA) were employed to identify the possible sources of the elements in the shellfish samples. Three principle components were extracted from the ionomic matrix and were associated with natural existence, biological pathways, and mining and smelting activities, respectively. The ionomic profiles of the shellfish samples were evaluated through hierarchical cluster analysis (HCA) which was exhibited in the form of heatmap. The shellfish samples were categorized according to the sampling sites with different contamination levels. Six As species including arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC) were separated and quantified using HPLC-ICP-MS. The concentrations of As(III) and As(V) were linearly increased with total As concentration increasing. However, the proportion of AsB was decreased with total As while the AsB concentration was irrelevant to total As.

Coupling nanoliter high-performance liquid chromatography to inductively coupled plasma mass spectrometry for arsenic speciation

Nanoliter high-performance liquid chromatography shows low consumption of solvents and samples, offering one of the best choices for arsenic speciation in precious samples in combination with inuctively coupled plasma mass spectrometry. A systematic investigation on coupling nanoliter high-performance liquid chromatography to inductively coupled plasma mass spectrometry from instrument design to injected sample volume and mobile phase was performed in this study. Nanoflow mobile phase was delivered by flow splitting using a conventional high-pressure pump with reuse of mobile phase waste. Dead volume was minimized to 60 nL for the sheathless interface based on the previously developed nanonebulizer. Capillary columns for nanoliter high-performance liquid chromatography were found to be sensitive to sample loading volume. An apparent difference was also found between the mobile phases for nanoliter and conventional high-performance liquid chromatography. Baseline separation of arsenite, arsenate, monomethylarsenic, and dimethylarsenic was achieved within 11 min on a 15 cm C₁₈ capillary column and within 12 min on a 25 cm strong anion exchange column. Detection limits of 0.9-1.8 μg/L were obtained with precisions variable in the range of 1.6-4.2%. A good agreement between determined and certified values of a certified reference material of human urine (GBW 09115) validated its accuracy along with good recoveries (87-102%).

Accumulation, translocation and conversion of six arsenic species in rice plants grown near a mine impacted city

Paddy rice (Oryza sativa L.) as the staple food in China was found to be efficient in accumulating arsenic (As) due to cultivated in flooded paddy soil. Uptake and translocation of As in rice plant depended on the As species. In this work, rice plant samples including roots, straws and grains as well as rhizosphere soils were collected from paddy fields near Changsha, a mine impacted city in Southern China. The total As concentrations in the collected samples were observed in the descending order as root > soil > straw > grain. The predominant As species detected in rice plants were inorganic forms: arsenite [As(III)] and arsenate [As(V)]. Except monomethylarsonate (MMA) and dimethylarsinate (DMA), other two organoarsenicals, arsenobetaine (AsB) and arsenocholine (AsC), were also detected in rice plants. DMA and AsB were mainly formed in rice roots with the assistance of microorganisms. MMA and AsC detected in straws might be derived from methylation and oxidation of As(III). The results of multiple linear regressions indicated that the straw As species were remarkable predictors of the corresponding grain As species. Demethylation or degradation of MMA, DMA and AsC were predicted when translocated from straw to grain.

Arsenic speciation and heavy metal distribution in polished rice grown in Guangdong Province, Southern China

Arsenic speciation and heavy metal distributions have been investigated in locally grown rice grains from Guangdong Province, Southern China. A total of 41 polished rice grain samples were collected throughout Guangdong Province. Arsenite (As(III)), as the predominant form found in the rice, was positively correlated (p<0.01) with total As (tAs) concentration. However, the percentage of As(III) reduced while tAs concentration increased (r=-0.361, p<0.05), due to restricted accumulation and translocation of As(III) in rice grains at high level of tAs. Statistical and geostatistical analyses were applied to investigate potential origins of heavy metals in rice. Only Cd, Cu and Ni were identified as influenced by anthropogenic sources such as industrial and commercial activities. As and Pb were primarily controlled by natural occurrence. The results of health risk assessment implied that continuous intake of rice grown in Guangdong Province could cause considerably non-carcinogenic and carcinogenic risk to local inhabitants.

Effects on heavy metal accumulation in freshwater fishes: species, tissues, and sizes

Three fish species (Carassius auratus, Pelteobagrus fulvidraco, and Squaliobarbus curriculus) were collected from Xiang River near Changsha City, Southern China. The concentrations of heavy metals including arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn) in the muscle, gill, and liver of three species were determined by the inductively coupled plasma mass spectrometry method. One-way analysis of variance (ANOVA) was introduced to determine the significant variations (p < 0.05) of heavy metals. Livers were found to accumulate Cd and Cu due to the metallothionein proteins. High levels of Mn and Pb in the gills indicated that the main uptake pathway of these heavy metals was from the water. The carnivorous species, P. fulvidraco, was found to accumulate the highest levels of toxic elements (As, Cd, and Pb), while relatively high concentrations of nutrient elements (Cu, Fe, Mn, and Zn) were accumulated in omnivorous species (C. auratus and S. curriculus). According to the results of Pearson's correlation analysis, there were few significant relationships at p < 0.01 level between the concentrations of the analyzed elements and the fish sizes. The results of risk assessment indicated that exposure to the toxic heavy metals from fish muscle consumption posed no non-carcinogenic health risk to local inhabitants.