Arsenite resistance and removal from aqueous solution by Rhosococcus sp AW3 isolated from soybean rhizosphere in an agricultural field from Cordoba

WEVAR OLLER AL; TALANO MA; PAISIO CE; MEDINA MI; AGOSTINI, E

Tucuman

Congreso; VII CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL “SAMIGE del BICENTENARIO; 2011

SAMIGE

Arsenic (As) in groundwater and soil, and its fate and transport in the environment have become matters of great concern in several countries. In agricultural environment, besides domestic use (drinking and cooking), huge quantities of water from As contaminated aquifer are usually used for irrigation purposes which increases As accumulation through the food chain. Moreover, with increased arsenic in soil and water, sustainable agriculture development is hindered by As phytoxicity and long-term impact on agricultural yield. Simple, environmentally-friendly and novel methods are needed for its removal from water and soil. For this purpose, the potential of different microbes in As removal has gained interest.  In this work we isolated an arsenite-resistant bacterium from the rhizosphere of soybean (Glycine max) plants grown in an intensive agricultural soil (Paraje La Escondida, Alcira Gigena, Córdoba, located at 32º40’83”S, 64º33’40”W). This strain was selected, among others, due to its high resistance to arsenite (As+3). On the basis of its morphological, cultural, physiological, biochemical characteristics, and supported by phylogenetic analysis based upon their 16S rRNA gene sequence, it was identified as Rhodococcus sp. and named as Rhodococcus sp. AW3. This strain grew in the presence of high sodium arsenite (NaAsO2) concentrations, over 38 mM, in solid YEMA (Yeast Extract Mannitol Agar). Induction experiments in YEM liquid media indicated that resistance mechanisms of this bacterium are constitutive. Qualitative oxidation experiments suggested that Rhodococcus sp. AW3 is not able to oxidize As+3.  In preliminary arsenite (As+3) removal assays liquid medium containing 5 mM NaAsO2, Rhodococcus sp. AW3 was able to remove about 62% of the contaminant. Because As+3 is more difficult to eliminate than As+5, currently, further studies are being conducted to establish the genetic factors that determine As resistance and the mechanisms responsible for As removal. Selection of appropriate bacteria for soil and water treatments will widen the perspectives of sustainable management of agricultural areas affected by As. In particular, the isolated native Rhodococcus sp. AW3 could prove to be useful in forthcoming experiments of As bioremediation in agricultural soils or eventually contaminated waters Sección Microbiología ambiental y del suelo