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Removal of arsenic from contaminated groundwater by goethite adsorption in the presence of the arsenite-oxidizing bacterium Aliihoeflea sp. strain 2WW
No full textContamination of aquifers with As has raised great concern, because of serious risks to human health. The revised drinking water standard for arsenic imposes a 10 μg L-1 threshold limit, which has boosted research efforts to remove As efficiently. Arsenic has a high affinity for adsorption to metal oxides, with As(V) being more effectively adsorbed than As(III). Consequently the oxidation of As(III) to As(V) is a prerequisite for achieving As concentrations below the threshold. Bio-oxidation of As(III) by microorganisms has recently received attention as a sustainable alternative to the use of chemical oxidants.
The aim of our work was to improve the removal of As from groundwater by oxidizing As(III) to As(V) followed by adsorption to goethite. For this purpose, we first isolated an arsenite-oxidizing bacterium, Aliihoeflea sp. strain 2WW, from a biofilm treating contaminated groundwater, and subsequently investigated the As(III) oxidation capability of this strain. The experiments were conducted in Tris-HCl 5 mM (pH 7.2) containing 200 μg L-1 of As, using As(III)-induced and non-induced resting cells. As(III) and As(V) adsorption capability of goethite was evaluated by using 4 g L-1 goethite and increasing As concentrations (25-800 μg L-1). Finally we tested the As-removal efficiency of the combined 2WW-goethite system on a synthetic contaminated water and a contaminated groundwater sample. Resting cells of an As(III)-induced culture of 2WW were able to oxidize completely 200 μg L-1 of As in 8 hours, while non-induced cells oxidized As in 24 hours. Subsequently, results from the As-adsorption experiments showed that goethite removed almost the complete 200 μg L-1 of As(V) from the solution, while for As(III) only 75% was adsorbed.
Our results indicate that As(III) oxidation by Aliihoeflea sp. strain 2WW combined with goethite adsorption is an efficient approach for the removal of As from contaminated groundwater.
Research funded by CARIPLO Foundation-2010-2221
Microbial Transformations of Arsenic in Groundwater
No full textArsenic occurs in water and soil either as a consequence of human activities or from natural leaching or dissolution of arsenic-rich minerals. The toxicological effects of arsenic are related to its chemical form and oxidation state: arsenite [As(III)] is about 100-times more toxic and mobile than arsenate [As(V)]. Human exposure to arsenic typically occurs through drinking water. The World Health Organization recommends 10 μgL-1 as a maximum arsenic concentration in drinking water. Groundwater of several Italian Regions, including Lombardia, Lazio, Puglia and Sardegna, have been found to contain As concentrations higher than 10 μg L-1 (D.Lgs. 31/2001) due to the complexity of the geological history and to substratum rock types of the regions. Arsenic can be removed from contaminated waters by physico-chemical as well as biological techniques. The former, however, have some limitations, such as the use of chemicals with environmental impact, the production of large amount of sludge, the need of secondary treatment, high costs and in some cases a low efficiency. The bacterial oxidation of As(III) to As(V) is being a promising technology for effective removal of As from ground water by decreasing its bioavailability. From contaminated water it can be converted into an insoluble compound and co-precipitated with the hydro-oxides of Fe and Mn. The aim of this project is to study the indigenous microbial communities of some As-rich groundwaters from Lombardia, to investigate the relationships between microbial populations and water characteristics (e.g., chemical composition and redox status), and to utilize As-oxidising bacteria as new agents for biological decontamination of drinking water.
The multidisciplinary approach adopted in the solution of the problem sees environmental chemists and microbiologists interacting with molecular biologists, with the objective to add knowledge and to complement the research on arsenic already carried out by the Environmental Microbiology Group of DiSTAM and by the Soil Chemistry group of DiProVe. Prof. Muyzer, who will coordinate the research together with Prof. Andreoni, is an internationally recognised molecular ecologist that will teach the Italian scientists to gain new laboratory skills and to deal with the management of research, from scientific data interpretation to technology transfer. The scientific collaboration with an internationally recognised researcher will enable the Italian team to create a new research network at international level, and to stimulate mobility through joint research partnerships in co-operation programmes between different organisations. The specific scientific impact of this proposal is to increase the knowledge of the quality of ground water in Lombardia with regard to the presence of As, one of the most toxic contaminant in drinking water, and to the development of an environment-harmless biological treatment.
The aims of the project fit with the general objectives of Fondazione CARIPLO, which finances this exchange program within the call “Promote the formation of human capital of excellence. Promoting international projects aimed at recruiting young researchers”
Impiego combinato di microrganismi e composti adsorbenti per la decontaminazione di acque di falda ricche di arsenico
No full textCharacterization of the arsenite oxidizer Aliihoeflea sp. strain 2WW and its potential application in the removal of arsenic from groundwater in combination with Pf-ferritin
No full textA heterotrophic arsenite-oxidizing bacterium, strain 2WW, was isolated from a biofilter treating arsenic-rich groundwater. Comparative analysis of 16S rRNA gene sequences showed that it was closely related (98.7 %) to the alphaproteobacterium Aliihoeflea aesturari strain N8T. However, it was physiologically different by its ability to grow at relatively low substrate concentrations, low temperatures and by its ability to oxidize arsenite. Here we describe the physiological features of strain 2WW and compare these to its most closely related relative, A. aestuari strain N8T. In addition, we tested its efficiency to remove arsenic from groundwater in combination with Pf-ferritin. Strain 2WW oxidized arsenite to arsenate between pH 5.0 and 8.0, and from 4 to 30 °C. When the strain was used in combination with a Pf-ferritin-based material for arsenic removal from natural groundwater, the removal efficiency was significantly higher (73 %) than for Pf-ferritin alone (64 %). These results showed that arsenite oxidation by strain 2WW combined with Pf-ferritin-based material has a potential in arsenic removal from contaminated groundwater
The microbial arsenic cycle in groundwater of Lombardia (Italy)
No full textArsenic in contaminated groundwater occurs largely as arsenite [As(III)], while As(V) is more prevalent in surface water. As the presence of arsenic species in drinking water, even in low concentrations, is a threat to human health, the World Health Organization recommends 10μgL-1 as the maximum arsenic concentration in drinking water. Groundwater of several Italian regions, has been found to contain As concentrations higher than 10μg L-1, due to the complexity of geological history and to substratum rock types of the regions. Within a project, financed by Fondazione Cariplo (Italy), aimed to study the indigenous microbial communities of As-rich groundwater from
Lombardia, we isolated bacteria involved in biogenic As cycle, i.e., in the reduction of As(V) and in the oxidation of As(III). Microbial species with arsenic biotransforming capability had so far not been studied in groundwater in Italy. The objectives of this study were to study the diversity and distribution of culturable As(V)-reducing and As(III)–oxidizing bacteria in groundwater with different Ascontaminated levels. Bacteria transforming As were isolated from all groundwater samples collected from 7 sites around Cremona (Lombardia, Italy). While bacteria able to reduce As(V) were isolated from each site, bacteria involved in the oxidation of reduced As
species were not always retrieved. In one site, the concomitant presence of an arsenate reducer and arsenite oxidizer was detected, indicating the occurrence of a full As cycle. For the first time, we provide evidence for the presence of an arsenite oxidase gene in an Aliihoeflea aestuarii strain and for its As(III)-oxidizing capability. The bacterial oxidation of As(III) to As(V) is being a promising technology for effective removal of As from groundwater as As(V) is more adsorptive to sorbents than As(III). Physico-chemical techniques that are usually used to remove arsenic from contaminated water have however some limitations, such as the use of chemicals
with environmental impact, the production of large amount of sludge, the need of secondary treatment, high costs and in some cases a low efficiency
Bacterial Communities Potentially Involved in Arsenic Cycle in Groundwaters from Lombardia (Italy)
No full textHuman exposure to arsenic typically occurs through drinking water and the World Health Organization indicates a maximum threshold of 10 μg L-1 in drinking water. The aim of our work was to investigate the relationships between microbial populations and type and composition of groundwaters, in order to understand the origin of arsenic contamination in groundwaters from the Northern part of Italy (Lombardia).
Water samples were collected from ten sites (six wells and four piezometers), chosen from the dataset of the Regional Agency for Health Prevention and Environmental Protection of Lombardia, and based on their different levels of arsenic content. Samples from piezometers showed lower pH values, significantly higher concentrations of total dissolved iron and manganese, and significantly higher values of electrical conductivity than samples from wells. The total arsenic concentration in groundwater samples ranged from 0.7 to 171 μg L-1. Samples from eight out of ten sites exceeded the 10 μg L-1 arsenic threshold (D.Lgs. 31/2001). In all the arsenic polluted samples, arsenite was dominant and the arsenite/arsenate ratio ranged from 4 to 7.
The microbial communities of 6 groundwater samples were determined by denaturing gradient gel electrophoresis and Pyrotag sequencing of 16S rRNA genes amplified from environmental DNA. Betaproteobacteria (retrieved in five samples), Gamma- and Epsilonproteobacteria (in four samples), and Alphaproteobacteria (in three samples) were the most represented classes. Bacterial populations of samples from wells and piezometers were correlated with the oxidation processes of sulfur (genera Sulfuricurvum and Thiothrix), iron (genera Gallionella, Sideroxydans, Thiobacillus and Magnetobacterium), manganese (genus Hyphomicrobium sp.) and nitrite (genus Nitrospira). Reductive processes of sulfur, nitrogen and of methylated compounds were displayed by the presence of genera Desulfovibrio sp., Denitratisoma sp. and of methylobacteria in all the samples, whereas dissimilatory iron reduction was displayed only in a piezometer sample by the presence of Geobacter sp.. Chemolithoautotrophic strains were confirmed to be present in some samples by the amplification of cbbL and cbbM genes, coding for the large subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) Type-I and Type-II, respectively. Bacterial genera described as able to cope with arsenic were present in groundwater samples, although no sequence belonged to known arsenic-metabolizing strain. This can be due either to a natural biodiversity of bacterial communities or to the presence of specific arsenic strains in number below the detection limit. Their presence was indeed evidenced by amplification of genes for arsenate respiratory reductase, ArrA, for arsenite oxidase, AioA (formerly referred to as AroA/AoxB), and for arsenate reductase (ArsC) in groundwater DNA.
The obtained data indicate that chemolithotrophic processes dominate at all the sites. In particular, two different arsenic metabolisms are present in the bacterial communities of these arsenic polluted groundwaters of Lombardia: arsenotrophy, growth coupled to arsenate dissimilatory reduction or autotrophic arsenite oxidation, and arsenic detoxification via cytoplasmatic arsenate reduction. In addition to these, reactions carried out by iron reducing and iron/manganese oxidising bacteria could be involved in the arsenic mobilization/immobilization processes from geological substrates to groundwaters.
Acknowledgment
Research supported by CARIPLO Foundation, project 2010-2221
Microbial transformations of arsenic : potential applications in decontamination actions
No full textArsenic occurs in water and soil either as a consequence of human activities or from natural leaching or dissolution of arsenic-rich minerals. The toxicological effects of arsenic are related to its chemical form and oxidation state: arsenite [As(III)] is about 100-times more toxic and mobile than arsenate [As(V)]. Human exposure to arsenic typically occurs through drinking water. The World Health Organization recommends 10 μgL-1 as a maximum arsenic concentration in drinking water. Groundwater of several Italian Regions, including Lombardia, Lazio, Puglia and Sardegna, have been found to contain As concentrations higher than 10 μg L-1 (D.Lgs. 31/2001) due to the complexity of the geological history and to substratum rock types of the regions. Arsenic can be removed from contaminated waters by physico-chemical as well as biological techniques. The former, however, have some limitations, such as the use of chemicals with environmental impact, the production of large amount of sludge, the need of secondary treatment, high costs and in some cases a low efficiency. The bacterial oxidation of As(III) to As(V) is being a promising technology for effective removal of As from ground water by decreasing its bioavailability. From contaminated water it can be converted into an insoluble compound and co-precipitated with the hydro-oxides of Fe and Mn. The aim of this project is to study the indigenous microbial communities of some As-rich groundwaters from Lombardia, to investigate the relationships between microbial populations and water characteristics (e.g., chemical composition and redox status), and to utilize As-oxidising bacteria as new agents for biological decontamination of drinking water.
The multidisciplinary approach adopted in the solution of the problem sees environmental chemists and microbiologists interacting with molecular biologists, with the objective to add knowledge and to complement the research on arsenic already carried out by the Environmental Microbiology Group of DiSTAM and by the Soil Chemistry group of DiProVe. Prof. Muyzer, who will coordinate the research together with Prof. Andreoni, is an internationally recognised molecular ecologist that will teach the Italian scientists to gain new laboratory skills and to deal with the management of research, from scientific data interpretation to technology transfer. The scientific collaboration with an internationally recognised researcher will enable the Italian team to create a new research network at international level, and to stimulate mobility through joint research partnerships in co-operation programmes between different organisations. The specific scientific impact of this proposal is to increase the knowledge of the quality of ground water in Lombardia with regard to the presence of As, one of the most toxic contaminant in drinking water, and to the development of an environment-harmless biological treatment.
The aims of the project fit with the general objectives of Fondazione CARIPLO, which finances this exchange program within the call “Promote the formation of human capital of excellence. Promoting international projects aimed at recruiting young researchers”
Arsenic transforming abilities of groundwater bacteria: combined use of strain 2WW and goethite in metalloid removal
No full textThe revised drinking water standard for arsenic imposes a 10 μg L-1 threshold limit (World Health Organisation), which has boosted research efforts to remove arsenic efficiently. Arsenic has a high affinity for adsorption to metal oxides, with arsenate [As(V)] being more effectively adsorbed than arsenite [As(III)]. Consequently the oxidation of As(III) to As(V) is a prerequisite for achieving arsenic concentrations below the threshold. Bacterial As(III)-oxidation is a promising step in the removal of arsenic from groundwater in combination with adsorbing materials such as goethite, as a sustainable alternative to the use of chemical oxidants.
The aim of our work was to study the indigenous microbial communities of arsenic-rich groundwater from Lombardia (Italy) and to isolate As(III) oxidizing bacteria in order to test the feasibility of an arsenic removal process that comprises biological oxidation of As(III) to As(V) followed by adsorption to goethite.
Water samples were collected from ten sites (six wells and four piezometers), chosen from the dataset of the Regional Agency for Health Prevention and Environmental Protection of Lombardia, and based on their different levels of arsenic content. Water samples were previously purged under controlled flow until stabilization of temperature, dissolved O2 and redox potential. pH and electrical conductivity (EC) were determined on refrigerated samples, within a few hours after collection. Iron, manganese and arsenic total contents were determined on acidified samples by ICP-MS (Agilent Technologies); for arsenic speciation, water samples were previously passed through a WATERS Sep-Pak_Plus Acell Plus QMA cartridge (Waters Corporation). Samples from piezometers showed lower pH values, significantly higher concentrations of total dissolved iron and manganese, and significantly higher values of electrical conductivity than samples from wells (p ≤ 0.05). The total arsenic concentration in groundwater samples ranged from 0.7 to 171 μg L-1. Samples from eight out of ten sites exceeded the 10 μg L-1 arsenic threshold (D.Lgs. 31/2001). In all the arsenic polluted samples, As(III) was dominant and the As(III)/As(V) ratio ranged from 4 to 7. Bacterial strains involved in the arsenic cycle, so far not been studied in groundwater in Italy, were isolated from successive enrichment transplants on As(III) or As(V) of groundwater samples. Twenty isolates able to reduce As(V) were retrieved from most of the sites. They were affiliated to different species of Pseudomonas, Achromobacter and Rhodococcus. They carried an ars detoxification system, as detected by PCR amplification of arsC and arsB genes for As(V) reductase and As(III) efflux pump, respectively. As(III) oxidising strains were more rare as only three isolates were able to produce As(V) from As(III). They belonged to Rhodococcus ruber, Achromobacter sp. and to Aliihoeflea aestuarii and aioA gene for As(III) oxidase was detected. In order to envisage the use of a bacterial strain in the As(III) oxidation step of the arsenic removal process, Aliihoeflea aestuarii strain 2WW was tested for its As(III) oxidation activity in different conditions of temperature and pH. It completely oxidized 1 mM As(III) within 24 h at 30°C, and within 96 h at 15° C. At 5°C the complete oxidation of As(III) occurred in 350 h. Complete As(III) oxidation occurred also in the pH range 5.0-8.0. Goethite was chosen as a model arsenic adsorbing material. The experiments were conducted in Tris-HCl 5 mM (pH 7.2) containing 200 μg L-1 of arsenic, using As(III)-induced and non-induced resting cells. As(III) and As(V) adsorption capability of goethite was evaluated by using 4 g L-1 goethite and increasing arsenic concentrations (25-800 μg L-1). Finally we tested the arsenic removal efficiency of the combined 2WW-goethite system on a synthetic contaminated water and a contaminated groundwater sample. Resting cells of an As(III)-induced culture of 2WW were able to oxidize completely 200 μg L-1 of As(III) in 8 hours, while non-induced cells oxidized As(III) in 24 hours. Subsequently, results from the arsenic adsorption experiments showed that goethite removed almost the complete 200 μg L-1 of As(V) from the solution, while only 75% As(III) was adsorbed, thus leaving in solution arsenic exceeding the 10 μg L-1 threshold limit.
Our results indicate that arsenic polluted groundwaters of Lombardia are reservoirs of bacterial populations able to transform arsenic, that may contribute to mobilization/immobilization of the metalloid in that environment. As(III) oxidation by Aliihoeflea aestuarii strain 2WW combined with goethite adsorption is envisaged as an efficient approach for the removal of arsenic from contaminated groundwater.
Research supported by CARIPLO Foundation, project 2010-222
A novel heterotrophic arsenite-oxidizing bacterium isolated from arsenic-polluted groundwater of Lombardia (Italy)
No full textArsenic contamination of aquifers is a threat to human health and the World Health Organization recommends 10 μgL-1 as the maximum arsenic concentration in drinking water. Groundwater of Lombardia (Italy) has been found to contain arsenic concentrations higher than the limit due to the substratum rock types of the site. Within a project, aimed to study the indigenous microbial communities of As-rich groundwater from Lombardia, we isolated an heterotrophic bacterium (strain 2WW) able to oxidise As(III). Here we present the characterization of this strain by evaluating the growth and As(III)-oxidation rate at different pH and temperature, and by investigating the presence of arsenic genes. Based on 16S rRNA gene sequence analysis, strain 2WW was most closely related to Aliihoeflea estuarii, affiliated to the Alphaproteobacteria. It completely oxidized 1 mM As(III) within 24 h at 30°C, and within 96 h at 15° C. At 5°C the complete oxidation of As(III) occurred in 350 h. Complete As(III) oxidation occurred also in the pH range 5.0-8.0. The strain carried an arsenite oxidase (aioA) gene highly similar to those of Rhizobiales, and an arsenite efflux pump (ACR3(2)) gene highly similar to the arsenite transporter of Hoeflea sp strain CH14.
For the first time, we provided evidence for the presence of an aioA gene in a bacterium affiliated to genus Aliihoeflea genus and for its As(III)-oxidizing capability. The bacterial As(III)-oxidation is being a promising first step in the removal of arsenic from groundwater, in combination with adsorbents.
Research supported by CARIPLO Foundation, project 2010-222
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