Bioremediation potential of the application of heavy-metal resistant actinobacteria and Zea mays plants onto polluted soil

CS BENIMELI; MA POLTI; VH ALBARRACÍN; CM ABATE; MJ AMOROSO

Biomanagement of Metal Contaminated Soils

Springer-Verlag

Lugar: Netherlands; Año: 2010;

Mining and industrial activities in Tucumán, Argentina have led to large-scale contamination of the environment with heavy metals which have been accumulated in soils, plants and animals. Thus, the screening and characterization of copper and chromium resistant microorganisms and plants is important for developing novel bioremediation and phytoremediation processes. Actinomycetes are Gram-positive bacteria with metabolical versatility and high morphologic diversity, which can be used in bioremediation experiences. High cadmium, nickel, chromium, mercury, copper and lead resistance levels were found in several actinomycetes strains. Maize (Z. mays L.) is a possible solution for the restoration of heavy metals-polluted soils. This plant has high biomass yields, heavy metal tolerance, and may create particularly good environmental conditions for soil microorganisms and microfauna. The aims of this work were: a) to analyze the potentiality of copper and chromium resistant actinomycetes strains to perform successful bioremediation process in polluted soils; b) to study the effects of different Cu concentrations on the root, shoot and leaf growth of maize and the copper uptake and accumulation by the plants; c) to propose the use of maize crops as bioindicators of the successful remediation process. Copper and chromium resistant actinobacteria strains were isolated from polluted soils which belonged to the genus Streptomyces and Amycolatopsis. The Cr reductor strains Streptomyces sp. MC1, Streptomyces sp. M3, Streptomyces sp. C55 y Streptomyces sp. R22, showed bioremediation ability in soil samples. These strains were able to reduce up to 85-95% of Cr (VI) (50 mg kg-1) after 21 days in soil samples, without any previous treatment, or addition of any substrate and with a normal soil humidity level. By other hand, Cr (VI) reduction and growth were not inhibited by natural soil microflora, confirming their potential to bioremediate polluted soils. The novel copper resistant actinobacterium Amycolatopsis tucumanensis DSM 45259 was used to bioaugment copper poluted soil microcosms. A. tucumanensis was capable of colonizing both, copper-polluted and non-polluted soils but also showed copper bioimmobilization ability as bioavailable Cu was 31% lower in soil solution as compared to non-bioaugmented soil. The results obtained when using Z. mays as bioindicator correlated well with the values obtained: 20 and 17% lower tissue contents of Cu were measured in roots and leaves, respectively. These results suggest the potential use of A. tucumanensis at great scale in copper soil bioremediation strategies as a copper bio-complexing microbe to exclude copper bioavailability for other organism living from soils. Cu accumulation by roots, shoots and leaves of Z. mays were examined using 10-4 to 10-2 M CuSO4, no inhibition of growth in the plants was observed. The tolerance index, based on root length, was not significantly different for the three different treatments. However, the total accumulation rate was very low at 10-4 and 10-3 M compared to 10-2 M. The capacity of copper accumulation by roots, shoots and leaves of Z. mays plants increased concomitant to the metal concentration, arriving to 382 times more in roots, 157 in shoots and only 16 in leaves, compared to the controls without CuSO4. Cu could be accumulated by roots, shoots and leaves when the initial concentrations were 10-3 and 10-4 M. However, when it was 10-2 M, the metal could not be accumulated by leaves and shoots, but the roots could increase their copper accumulation capacity three times compared to the control. Z. mays could have potential ability to accumulate Cu without being overly sensitive to Cu toxicity.