Saturday, 15 July 2006

Culturable Bacterial Populations in Arsenic Polluted Soils of the South West Bangladesh.

Elena Dell'Amico1, Lucia Cavalca1, Laura Terruzzi1, Luigi Allievi1, Maria Martin2, and Vincenza Andreoni1. (1) Univ degli Studi di Milano, Via Celoria, 2, Milan, Italy, (2) DIVAPRA, Univ of Turin, via L. da Vinci 44, Grugliasco, 10095, Italy

Inorganic arsenic (As) exists in two major forms: the reduced form, arsenite, and the oxidized form, arsenate. In Bangladesh, arsenic contamination of groundwaters and soils is a serious environmental hazard and a national health problem. Several bacteria are involved in As transformation, and their activity is significant in that the different As species vary in solubility, mobility, bioavailability and toxicity. While arsenite shows greater toxicity and is more mobile under most environmental conditions, arsenate is the thermodynamically favorable form in aerobic waters. The present study determined the numbers of culturable arsenate- and arsenite-tolerant bacteria present in a silty clay loam paddy soil and in a silt loam soil (“Dahl” soil) of the Satkhira District. In the paddy soil, the percentage of arsenite-tolerant bacteria was threefold that found in the “Dahl” soil. DGGE was used to obtain DNA fingerprints of the bacterial community of enrichment cultures and of the total culturable and As(V)- and As(III)-tolerant heterotrophs in the “Dhal” and paddy soils. The objectives were addressed through experiments involving various millimolar concentrations of either As (V) or As (III), used to enrich microorganisms potentially able to transform As under aerobic conditions. The As(III) and As(V) treatments produced somewhat different banding patterns, indicating that the enrichment conditions influenced the population selection of soil bacteria adapted to such conditions. The culturable As(V)- and As(III)-tolerant bacteria did not display such a marked differences. Different arrays of arsenate- and arsenite-resistant isolates were obtained and the diversity of these strains is described. Given their high resistance to As, some of these strains are potential candidates for the bioremediation of environments heavily contaminated by As.

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