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

Abstract

The screening and characterization of metal resistant microorganisms and plants is important for developing novel bioremediation and phytoremediation processes. In that sense, 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. Our results indicate the feasibility of using copper and chromium resistant actinobacteria to efficiently bioremediate polluted soils. Four Cr resistant Streptomyces strains were able to reduce up to 85-95% of Cr (VI) (50 mg kg-1) after 21 days incubated in soil samples. In turn, the novel copper resistant actinobacterium Amycolatopsis tucumanensis showed efficient copper bioimmobilization ability when inoculated onto copper polluted soil microcosms: bioavailable Cu was 31% lower in soil solution as compared to non-bioaugmented soil. Conversely, Zea mays plants probed to be interesting as both, biomarker and bioremediation tools. The results obtained when using Z. mays as bioindicator of the successful bioremediation process of A. tucumanensis in polluted soil microcosms correlated well with the values obtained with chemical and physical methods: 20 and 17% lower tissue contents of Cu were measured in roots and leaves, respectively. Z. mays showed also a great capacity for copper accumulation by roots, shoots and leaves which increased concomitant to the metal concentration tested, reaching to 382 times more in roots, 157 in shoots and only 16 in leaves, compared to the controls without CuSO4. As no alteration in plant morphology was observed, Z. mays could have potential ability to accumulate Cu without being overly sensitive to Cu toxicity.