Human 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.
Bacterial Communities Potentially Involved in Arsenic Cycle in Groundwaters from Lombardia (Italy) / L. Cavalca, P. Zaccheo, A. Corsini, B. Abbas, V. Andreoni, G. Muyzer - In: International conference ISME 14: The power of small[s.l] : International Society of Microbial Ecology, 2012 Aug. (( Intervento presentato al 14. convegno International conference ISME : The power of small tenutosi a Copenhagen (Denmark) nel 2012.
|Titolo:||Bacterial Communities Potentially Involved in Arsenic Cycle in Groundwaters from Lombardia (Italy)|
CAVALCA, LUCIA (Primo)
ZACCHEO, PATRIZIA (Secondo)
ANDREONI, VINCENZINA (Penultimo)
|Settore Scientifico Disciplinare:||Settore AGR/16 - Microbiologia Agraria|
Settore AGR/13 - Chimica Agraria
|Data di pubblicazione:||ago-2012|
|Tipologia:||Book Part (author)|
|Appare nelle tipologie:||03 - Contributo in volume|